Recent Postings from Cosmology and Extragalactic

The Star-Formation History of BCGs to z = 1.8 from the SpARCS/SWIRE Survey: Evidence for significant in-situ star formation at high-redshift

We present the results of a MIPS-24um study of the Brightest Cluster Galaxies (BCGs) of 535 high-redshift galaxy clusters. The clusters are drawn from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), which effectively provides a sample selected on total stellar mass, over 0.2 < z < 1.8 within the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey fields. 20%, or 106 clusters have spectroscopically confirmed redshifts, and the rest have redshifts estimated from the color of their red sequence. A comparison with the public SWIRE images detects 125 individual BCGs at 24um > 100uJy, or 23%. The luminosity-limited detection rate of BCGs in similar richness clusters (Ngal> 12) increases rapidly with redshift. Above z ~ 1, an average of ~20\% of the sample have 24um-inferred infrared luminosities of LIR > 10^12 Lsun, while the fraction below z ~ 1 exhibiting such luminosities is < 1 \%. The Spitzer-IRAC colors indicate the bulk of the 24um-detected population is predominantly powered by star formation, with only 7/125 galaxies lying within the color region inhabited by Active Galactic Nuclei (AGN). Simple arguments limit the star-formation activity to several hundred million years and this may therefore be indicative of the timescale for AGN feedback to halt the star formation. Below redshift z ~ 1 there is not enough star formation to significantly contribute to the overall stellar mass of the BCG population, and therefore BCG growth is likely dominated by dry-mergers. Above z~ 1, however, the inferred star formation would double the stellar mass of the BCGs and is comparable to the mass assembly predicted by simulations through dry mergers. We cannot yet constrain the process driving the star formation for the overall sample, though a single object studied in detail is consistent with a gas-rich merger.

Is $\Lambda$CDM an effective CCDM cosmology? [Cross-Listing]

We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the Universe mimics exactly the observed flat accelerating $\Lambda$CDM cosmology with just one dynamical free parameter. This kind of creation cold dark matter (CCDM) scenario provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to $\Lambda$CDM both at the background and perturbative levels and is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because $\Lambda$CDM may be only an effective cosmology

Complexity Induced Sporadic Localized Multifractal Antiscreening in Gravitational Evolution at Large Scales [Cross-Listing]

It has been suggested that antiscreening effects due to the running of the gravitational constant G might provide a partial solution to the dark matter mystery. It has also been hypothesized that renormalization group scaling transformations at large scales might supply the theoretical explanation. In this letter, we demonstrate that multifractal coarse-graining scaling effects due to classical fluctuations in the IR with consecutive symmetry breakings in gravitational evolution and induced running of the gravitational constant with fractal structures at larger scales may provide the plausible explanation of the observed results of weak lensing observations and beyond. The sporadic and localized antiscreening due to the running of the gravitational constant can also provide the backbone for the cosmic evolution and large scale structure formation. Our interpretation of this interesting finding is that such effects are the result of the complexity phenomenon involving the evolution of large-scale multifractal structures and accompanying fluctuations, not the conventional arguments suggesting quantum gravity being the primary cause. We also suggest that the running of the cosmological constant due to such stochastic complexity evolution may provide a key to the understanding of the observed cosmic acceleration.

Angular momentum evolution for galaxies in a Lambda-CDM scenario

Galaxy formation in the current cosmological paradigm is a very complex process in which inflows, outflows, interactions and mergers are common events. These processes can redistribute the angular momentum content of baryons. Recent observational results suggest that disc formed conserving angular momentum while elliptical galaxies, albeit losing angular momentum, determine a correlation between the specific angular momentum of the galaxy and the stellar mass. These observations provide stringent constraints for galaxy formation models in a hierarchical clustering scenario. We aim to analyse the specific angular momentum content of the disc and bulge components as a function of virial mass, stellar mass and redshift. We also estimate the size of the simulated galaxies and confront them with observations. We use cosmological hydrodynamical simulations that include an effective, physically-motivated Supernova feedback which is able to regulate the star formation in haloes of different masses. We analyse the morphology and formation history of a sample of galaxies in a cosmological simulation by performing a bulge-disc decomposition of the analysed systems and their progenitors. We estimate the angular momentum content of the stellar and gaseous discs, stellar bulges and total baryons. In agreement with recent observational findings, our simulated galaxies have disc and spheroid components whose specific angular momentum contents determine correlations with the stellar and dark matter masses with the same slope, although the spheroidal components are off-set by a fixed fraction. Abridged.

The New Numerical Galaxy Catalog ($\nu^2$GC): An Updated Semi-analytic Model of Galaxy and AGN with Large Cosmological N-body Simulations

We present a new cosmological galaxy formation model, $\nu^2$GC, as the updated version of our previous model $\nu$GC. We adopt the so-called "semi-analytic" approach, in which the formation history of dark matter halos is computed by N-body simulations, while the baryon physics such as gas cooling, star formation and supernova feedback are simply modeled by phenomenological equations. Major updates of the model are as follows: (1) the merger trees of dark matter halos are constructed in state-of-the-art N-body simulations, (2) we introduce the formation and evolution process of supermassive black holes and the suppression of gas cooling due to active galactic nucleus (AGN) activity, (3) we include heating of the intergalactic gas by the cosmic UV background, and (4) we tune the parameters using a Markov chain Monte Carlo method. Our N-body simulations of dark matter halos have unprecedented box size and mass resolution (the largest simulation contains 550 billion particles in a 1.12 Gpc/h box), enabling the study of much smaller and rarer objects. The model was tuned to fit the luminosity functions of local galaxies and mass function of neutral hydrogen. Local observations, such as the Tully-Fisher relation, size-magnitude relation of spiral galaxies and scaling relation between the bulge mass and black hole mass were well reproduced by the model. Moreover, the model also well reproduced the cosmic star formation history and the redshift evolution of rest-frame K-band luminosity function. The numerical catalog of the simulated galaxies and AGNs is publicly available on the web.

Fitting and forecasting non-linear coupled dark energy

We consider cosmological models in which dark matter feels a fifth force mediated by the dark energy scalar field, also known as coupled dark energy. Our interest resides in estimating forecasts for future surveys like Euclid when we take into account non-linear effects, relying on new fitting functions that reproduce the non-linear matter power spectrum obtained from N-body simulations. We obtain fitting functions for models in which the dark matter-dark energy coupling is constant. Their validity is demonstrated for all available simulations in the redshift range $z=0-1.6$ and wave modes below $k=10 \text{h/Mpc}$. These fitting formulas can be used to test the predictions of the model in the non-linear regime without the need for additional computing-intensive N-body simulations. We then use these fitting functions to perform forecasts on the constraining power that future galaxy-redshift surveys like Euclid will have on the coupling parameter, using the Fisher matrix method for galaxy clustering (GC) and weak lensing (WL). We find that by using information in the non-linear power spectrum, and combining the GC and WL probes, we can constrain the dark matter-dark energy coupling constant squared, $\beta^{2}$, with precision smaller than 4\% and all other cosmological parameters better than 1\%, which is a considerable improvement of more than an order of magnitude compared to corresponding linear power spectrum forecasts with the same survey specifications.

The Standard Model cross-over on the lattice

With the physical Higgs mass the Standard Model symmetry restoration phase transition is a smooth cross-over. We study the thermodynamics of the cross-over using numerical lattice Monte Carlo simulations of an effective SU(2) X U(1) gauge + Higgs theory, significantly improving on previously published results. We measure the Higgs field expectation value, thermodynamic quantities like pressure, energy density, speed of sound and heat capacity, and screening masses associated with the Higgs and Z fields. While the cross-over is smooth, it is very well defined with a width of only approximately 5 GeV. We measure the cross-over temperature from the maximum of the susceptibility of the Higgs condensate, with the result $T_c = 159.5 \pm 1.5$ GeV. Outside of the narrow cross-over region the perturbative results agree well with non-perturbative ones.

The Standard Model cross-over on the lattice [Cross-Listing]

With the physical Higgs mass the Standard Model symmetry restoration phase transition is a smooth cross-over. We study the thermodynamics of the cross-over using numerical lattice Monte Carlo simulations of an effective SU(2) X U(1) gauge + Higgs theory, significantly improving on previously published results. We measure the Higgs field expectation value, thermodynamic quantities like pressure, energy density, speed of sound and heat capacity, and screening masses associated with the Higgs and Z fields. While the cross-over is smooth, it is very well defined with a width of only approximately 5 GeV. We measure the cross-over temperature from the maximum of the susceptibility of the Higgs condensate, with the result $T_c = 159.5 \pm 1.5$ GeV. Outside of the narrow cross-over region the perturbative results agree well with non-perturbative ones.

The Standard Model cross-over on the lattice [Cross-Listing]

With the physical Higgs mass the Standard Model symmetry restoration phase transition is a smooth cross-over. We study the thermodynamics of the cross-over using numerical lattice Monte Carlo simulations of an effective SU(2) X U(1) gauge + Higgs theory, significantly improving on previously published results. We measure the Higgs field expectation value, thermodynamic quantities like pressure, energy density, speed of sound and heat capacity, and screening masses associated with the Higgs and Z fields. While the cross-over is smooth, it is very well defined with a width of only approximately 5 GeV. We measure the cross-over temperature from the maximum of the susceptibility of the Higgs condensate, with the result $T_c = 159.5 \pm 1.5$ GeV. Outside of the narrow cross-over region the perturbative results agree well with non-perturbative ones.

Polarized CMB recovery with sparse component separation

The polarization modes of the cosmological microwave background are an invaluable source of information for cosmology, and a unique window to probe the energy scale of inflation. Extracting such information from microwave surveys requires disentangling between foreground emissions and the cosmological signal, which boils down to solving a component separation problem. Component separation techniques have been widely studied for the recovery of CMB temperature anisotropies but quite rarely for the polarization modes. In this case, most component separation techniques make use of second-order statistics to discriminate between the various components. More recent methods, which rather emphasize on the sparsity of the components in the wavelet domain, have been shown to provide low-foreground, full-sky estimate of the CMB temperature anisotropies. Building on sparsity, the present paper introduces a new component separation technique dubbed PolGMCA (Polarized Generalized Morphological Component Analysis), which refines previous work to specifically tackle the estimation of the polarized CMB maps: i) it benefits from a recently introduced sparsity-based mechanism to cope with partially correlated components, ii) it builds upon estimator aggregation techniques to further yield a better noise contamination/non-Gaussian foreground residual trade-off. The PolGMCA algorithm is evaluated on simulations of full-sky polarized microwave sky simulations using the Planck Sky Model (PSM), which show that the proposed method achieve a precise recovery of the CMB map in polarization with low noise/foreground contamination residuals. It provides improvements with respect to standard methods, especially on the galactic center where estimating the CMB is challenging.

Oscillation in power spectrum of primordial gravitational wave as a signature of higher-order stringy corrections

In low-energy effective string theory, $\alpha’$ corrections involve the coupling of the dilaton field to higher-order curvature terms. By numerical method, we find that such corrections may bring unusual oscillations to the inflationary gravitational wave spectrum, which can be measurably imprinted in the cosmic microwave background (CMB) B-mode polarization. We analytically show that the intensity of the oscillations is determined by the string scale $M_s$ and the string coupling $g_s$.

Oscillation in power spectrum of primordial gravitational wave as a signature of higher-order stringy corrections [Cross-Listing]

In low-energy effective string theory, $\alpha’$ corrections involve the coupling of the dilaton field to higher-order curvature terms. By numerical method, we find that such corrections may bring unusual oscillations to the inflationary gravitational wave spectrum, which can be measurably imprinted in the cosmic microwave background (CMB) B-mode polarization. We analytically show that the intensity of the oscillations is determined by the string scale $M_s$ and the string coupling $g_s$.

Modelling Galaxy Clustering: Halo Occupation Distribution versus Subhalo Matching

We model the luminosity-dependent projected and redshift-space two-point correlation functions (2PCFs) of the Sloan Digital Sky Survey (SDSS) DR7 Main galaxy sample, using the halo occupation distribution (HOD) model and the subhalo abundance matching (SHAM) model and its extension. All the models are built on the same high-resolution $N$-body simulations. We find that the HOD model generally provides the best performance in reproducing the clustering measurements in both projected and redshift spaces. The SHAM model with the same halo-galaxy relation for central and satellite galaxies (or distinct haloes and subhaloes), when including scatters, has a best-fitting $\chi^2/\rm{dof}$ around $2$–$3$. We therefore extend the SHAM model to the subhalo clustering and abundance matching (SCAM) by allowing the central and satellite galaxies to have different galaxy–halo relations. We infer the corresponding halo/subhalo parameters by jointly fitting the galaxy 2PCFs and abundances and consider subhaloes selected based on three properties, the mass $M_{\rm acc}$ at the time of accretion, the maximum circular velocity $V_{\rm acc}$ at the time of accretion, and the peak maximum circular velocity $V_{\rm peak}$ over the history of the subhaloes. The three subhalo models work well for luminous galaxy samples (with luminosity above $L_*$). For low-luminosity samples, the $V_{\rm acc}$ model stands out in reproducing the data, with the $V_{\rm peak}$ model slightly worse, while the $M_{\rm acc}$ model fails to fit the data. We discuss the implications of the modeling results.

Neutral hydrogen structures trace dust polarization angle: Implications for the interstellar medium and CMB foregrounds

Using high-resolution data from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) survey, we show that linear structure in Galactic neutral hydrogen (HI) correlates with the magnetic field orientation implied by Planck 353 GHz polarized dust emission. The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. At high Galactic latitudes, where the Planck data are noise-dominated, the HI data provide an independent constraint on the Galactic magnetic field orientation, and hence the local dust polarization angle. We detect strong cross-correlations between template maps constructed from estimates of dust intensity combined with either HI-derived angles, starlight polarization angles, or Planck 353 GHz angles. The HI data thus provide a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination.

Eulerian BAO Reconstructions and N-Point Statistics

As galaxy surveys begin to measure the imprint of baryonic acoustic oscillations (BAO) on large-scale structure at the sub-percent level, reconstruction techniques that reduce the contamination from nonlinear clustering become increasingly important. Inverting the nonlinear continuity equation, we propose an Eulerian growth-shift reconstruction algorithm that does not require the displacement of any objects, which is needed for the standard Lagrangian BAO reconstruction algorithm. In our simulations, the algorithm yields 95% of the BAO signal-to-noise obtained from standard reconstruction. The reconstructed power spectrum is obtained by adding specific simple 3- and 4-point statistics to the pre-reconstruction power spectrum, making it very transparent how additional BAO information from higher-point statistics is included in the power spectrum through the reconstruction process. Analytical models of the reconstructed density for the two algorithms agree at second order. Based on similar modeling efforts, we introduce four additional reconstruction algorithms and discuss their performance.

Electrodynamics on Cosmological Scales [Cross-Listing]

Maxwell’s equations cannot describe a homogeneous and isotropic universe with a uniformly distributed net charge, because the electromagnetic field tensor in such a universe must be vanishing everywhere. For a closed universe with a nonzero net charge Maxwell’s equations always fail regardless of the spacetime symmetry and the charge distribution. The two paradoxes indicate that Maxwell’s equations need to be modified to be applicable to the universe as a whole. We consider two types of modified Maxwell equations, both of which can address the paradoxes. One is the Proca-type equation, which contains a photon mass term, i.e., a term proportional to the vector potential of the electromagnetic field. We show that this term can naturally arise if the electromagnetic field is coupled to a complex scalar field. If the complex scalar field is interpreted as describing charged pion particles, the mean mass density of charged pions in the universe gives rise to an effective photon mass with a Compton wavelength comparable to the Hubble radius of the universe. The other type of modified Maxwell equations contains a term with the electromagnetic field potential vector coupled to the spacetime curvature tensor. We show that this term can naturally arise if the Maxwell equation in a flat spacetime is written in terms of a symmetric tensor instead of the anti-symmetric tensor and then extended to a curved spacetime through the "minimal substitution rule". Some consequences of the modified Maxwell equations are investigated. The results show that for reasonable parameters the modification does not affect existing experiments and observations. However, we argue that, the modified equations may be testable in appropriate astrophysical and cosmological environments.

Vortical Motions of Baryonic Gas in the Cosmic Web: Growth History and Scaling Relation

The vortical motions of the baryonic gas residing in large scale structures are investigated by cosmological hydrodynamic simulations. Proceeding in the formation of the cosmic web, the vortical motions of baryonic matter are pumped up by baroclinity in two stages, i.e., the formation of sheets, and filaments. The mean curl velocity are about $< 1$, 1-10, 10-150, 5-50 km/s in voids, sheets, filaments and knots at $z=0$, respectively. The scaling of the vortical velocity of gas can be well described by the She-Leveque hierarchical turbulence model in the range of $l<0.65(1.50) h^{-1}$ Mpc in simulation of box size 25(100) $h^{-1}$ Mpc. The fractal Hausdorff dimension of vortical motions, $d$, revealed by velocity structure functions, is $\sim 2.1-2.3$($\sim 1.8-2.1$). It is slightly larger than the fractal dimension of mass distribution in filaments, $\textit{D}^f \sim 1.9-2.2$, and smaller than the fractal dimension of sheets, $\textit{D}^s \sim 2.4-2.7$. The vortical kinetic energy of baryonic gas is mainly transported by filaments. Both the scaling of mass distribution and vortical velocity increments show distinctive transition at the turning scale of $\sim 0.65(1.50) h^{-1}$ Mpc, which may be closely related to the characteristic radius of density filaments.

Cosmology Beyond Einstein [Cross-Listing]

The accelerating expansion of the Universe poses a major challenge to our understanding of fundamental physics. One promising avenue is to modify general relativity and obtain a new description of the gravitational force. Because gravitation dominates the other forces mostly on large scales, cosmological probes provide an ideal testing ground for theories of gravity. In this thesis, we describe two complementary approaches to the problem of testing gravity using cosmology. In the first part, we discuss the cosmological solutions of massive gravity and its generalisation to a bimetric theory. These theories describe a graviton with a small mass, and can potentially explain the late-time acceleration in a technically-natural way. We describe these self-accelerating solutions and investigate the cosmological perturbations in depth, beginning with an investigation of their linear stability, followed by the construction of a method for solving these perturbations in the quasistatic limit. This allows the predictions of stable bimetric models to be compared to observations of structure formation. Next, we discuss prospects for theories in which matter "doubly couples" to both metrics, and examine the cosmological expansion history in both massive gravity and bigravity with a specific double coupling which is ghost-free at low energies. In the second and final part, we study the consequences of Lorentz violation during inflation. We consider Einstein-aether theory, in which a vector field spontaneously breaks Lorentz symmetry and couples nonminimally to the metric, and allow the vector to couple in a general way to a scalar field. Specialising to inflation, we discuss the slow-roll solutions in background and at the perturbative level. The system exhibits a severe instability which places constraints on such a vector-scalar coupling to be at least five orders of magnitude stronger [...]

Cosmology Beyond Einstein [Cross-Listing]

The accelerating expansion of the Universe poses a major challenge to our understanding of fundamental physics. One promising avenue is to modify general relativity and obtain a new description of the gravitational force. Because gravitation dominates the other forces mostly on large scales, cosmological probes provide an ideal testing ground for theories of gravity. In this thesis, we describe two complementary approaches to the problem of testing gravity using cosmology. In the first part, we discuss the cosmological solutions of massive gravity and its generalisation to a bimetric theory. These theories describe a graviton with a small mass, and can potentially explain the late-time acceleration in a technically-natural way. We describe these self-accelerating solutions and investigate the cosmological perturbations in depth, beginning with an investigation of their linear stability, followed by the construction of a method for solving these perturbations in the quasistatic limit. This allows the predictions of stable bimetric models to be compared to observations of structure formation. Next, we discuss prospects for theories in which matter "doubly couples" to both metrics, and examine the cosmological expansion history in both massive gravity and bigravity with a specific double coupling which is ghost-free at low energies. In the second and final part, we study the consequences of Lorentz violation during inflation. We consider Einstein-aether theory, in which a vector field spontaneously breaks Lorentz symmetry and couples nonminimally to the metric, and allow the vector to couple in a general way to a scalar field. Specialising to inflation, we discuss the slow-roll solutions in background and at the perturbative level. The system exhibits a severe instability which places constraints on such a vector-scalar coupling to be at least five orders of magnitude stronger [...]

Primordial scalar power spectrum from the Euclidean bounce of loop quantum cosmology [Cross-Listing]

In effective models of loop quantum cosmology, the holonomy corrections lead to a deformed algebra of constraints. Among other consequences of this new spacetime structure is the emergence of an Euclidean phase around the bounce. In this article, we explicitly compute the resulting primordial power spectrum for scalar modes by setting initial conditions in the contracting phase.

Primordial scalar power spectrum from the Euclidean bounce of loop quantum cosmology [Cross-Listing]

In effective models of loop quantum cosmology, the holonomy corrections lead to a deformed algebra of constraints. Among other consequences of this new spacetime structure is the emergence of an Euclidean phase around the bounce. In this article, we explicitly compute the resulting primordial power spectrum for scalar modes by setting initial conditions in the contracting phase.

Multivariate Approaches to Classification in Extragalactic Astronomy

Clustering objects into synthetic groups is a natural activity of any science. Astrophysics is not an exception and is now facing a deluge of data. For galaxies, the one-century old Hubble classification and the Hubble tuning fork are still largely in use, together with numerous mono-or bivariate classifications most often made by eye. However, a classification must be driven by the data, and sophisticated multivariate statistical tools are used more and more often. In this paper we review these different approaches in order to situate them in the general context of unsupervised and supervised learning. We insist on the astrophysical outcomes of these studies to show that multivariate analyses provide an obvious path toward a renewal of our classification of galaxies and are invaluable tools to investigate the physics and evolution of galaxies.

Friedmann--Lemaitre Cosmologies via Roulettes and Other Analytic Methods [Cross-Listing]

In this work a series of methods are developed for understanding the Friedmann equation when it is beyond the reach of the Chebyshev theorem. First it will be demonstrated that every solution of the Friedmann equation admits a representation as a roulette such that information on the latter may be used to obtain that for the former. Next the Friedmann equation is integrated for a quadratic equation of state and for the Randall–Sundrum II universe, leading to a harvest of a rich collection of new interesting phenomena. Finally an analytic method is used to isolate the asymptotic behavior of the solutions of the Friedmann equation, when the equation of state is of an extended form which renders the integration impossible, and to establish a universal exponential growth law.

Friedmann--Lemaitre Cosmologies via Roulettes and Other Analytic Methods [Cross-Listing]

In this work a series of methods are developed for understanding the Friedmann equation when it is beyond the reach of the Chebyshev theorem. First it will be demonstrated that every solution of the Friedmann equation admits a representation as a roulette such that information on the latter may be used to obtain that for the former. Next the Friedmann equation is integrated for a quadratic equation of state and for the Randall–Sundrum II universe, leading to a harvest of a rich collection of new interesting phenomena. Finally an analytic method is used to isolate the asymptotic behavior of the solutions of the Friedmann equation, when the equation of state is of an extended form which renders the integration impossible, and to establish a universal exponential growth law.

Primordial non-Gaussianities after Planck 2015: an introductory review

Deviations from Gaussian statistics of the cosmological density fluctuations, so-called primordial non-Gaussianities (NG), are one of the most informative fingerprints of the origin of structures in the universe. Indeed, they can probe physics at energy scales inaccessible to laboratory experiments, and are sensitive to the interactions of the field(s) that generated the primordial fluctuations, contrary to the Gaussian linear theory. As a result, they can discriminate between inflationary models that are otherwise almost indistinguishable. In this short review, we explain how to compute the non-Gaussian properties in any inflationary scenario. We review the theoretical predictions of several important classes of models. We then describe the ways NG can be probed observationally, and we highlight the recent constraints from the Planck mission, as well as their implications. We finally identify well motivated theoretical targets for future experiments and discuss observational prospects.

Approach to exact solutions of cosmological perturbations: Tachyon field inflation [Cross-Listing]

An inflationary universe scenario in the context of tachyon field is studied. This study is done from an ansantz for the effective potential of cosmological perturbations $U(\eta)$. We describe in great detail the analytical solutions of the scalar and tensor perturbations for two different ansantz in the effective potential of cosmological perturbations; the Easther’s model and an effective potential similar to power law inflation. Also we find from the background equations that the effective tachyonic potential $V(\varphi)$, in both models satisfy the properties of a tachyonic potential. We consider the recent data from the Planck data to constrain the parameters in our effective potential of cosmological perturbations.

Approach to exact solutions of cosmological perturbations: Tachyon field inflation [Cross-Listing]

An inflationary universe scenario in the context of tachyon field is studied. This study is done from an ansantz for the effective potential of cosmological perturbations $U(\eta)$. We describe in great detail the analytical solutions of the scalar and tensor perturbations for two different ansantz in the effective potential of cosmological perturbations; the Easther’s model and an effective potential similar to power law inflation. Also we find from the background equations that the effective tachyonic potential $V(\varphi)$, in both models satisfy the properties of a tachyonic potential. We consider the recent data from the Planck data to constrain the parameters in our effective potential of cosmological perturbations.

Deforming regular black holes [Cross-Listing]

In this work, we have deformed regular black holes which possess a general mass term described by a function which generalizes the Bardeen and Hayward mass terms. Using linear constraints in the energy-momentum tensor, the solutions are either regular or singular. That is, with this approach, it is possible to generate singular black holes from regular black holes and vice versa. Moreover, contrary to the Bardeen and Hayward regular solutions, the regular deformed metrics may violate the weak energy condition despite the presence of the spherical symmetry. Some comments on accretion of deformed black holes in cosmological scenarios are made.

Shift Symmetry and Higgs Inflation in Supergravity with Observable Gravitational Waves [Cross-Listing]

We demonstrate how to realize within supergravity a novel chaotic-type inflationary scenario driven by the radial parts of a conjugate pair of Higgs superfields causing the spontaneous breaking of a grand unified gauge symmetry at a scale assuming the value of the supersymmetric grand unification scale. The superpotential is uniquely determined at the renormalizable level by the gauge symmetry and a continuous R symmetry. We select two types of Kahler potentials, which respect these symmetries as well as an approximate shift symmetry. In particular, they include in a logarithm a dominant shift-symmetric term proportional to a parameter c- together with a small term violating this symmetry and characterized by a parameter c+. In both cases, imposing a lower bound on c-, inflation can be attained with subplanckian values of the original inflaton, while the corresponding effective theory respects perturbative unitarity for r+-=c+/c-<1. These inflationary models do not lead to overproduction of cosmic defects, are largely independent of the one-loop radiative corrections and accommodate, for natural values of r+-, observable gravitational waves consistently with all the current observational data. The inflaton mass is mostly confined in the range (3.7-8.1)x10^10 GeV.

Shift Symmetry and Higgs Inflation in Supergravity with Observable Gravitational Waves

We demonstrate how to realize within supergravity a novel chaotic-type inflationary scenario driven by the radial parts of a conjugate pair of Higgs superfields causing the spontaneous breaking of a grand unified gauge symmetry at a scale assuming the value of the supersymmetric grand unification scale. The superpotential is uniquely determined at the renormalizable level by the gauge symmetry and a continuous R symmetry. We select two types of Kahler potentials, which respect these symmetries as well as an approximate shift symmetry. In particular, they include in a logarithm a dominant shift-symmetric term proportional to a parameter c- together with a small term violating this symmetry and characterized by a parameter c+. In both cases, imposing a lower bound on c-, inflation can be attained with subplanckian values of the original inflaton, while the corresponding effective theory respects perturbative unitarity for r+-=c+/c-<1. These inflationary models do not lead to overproduction of cosmic defects, are largely independent of the one-loop radiative corrections and accommodate, for natural values of r+-, observable gravitational waves consistently with all the current observational data. The inflaton mass is mostly confined in the range (3.7-8.1)x10^10 GeV.

Shift Symmetry and Higgs Inflation in Supergravity with Observable Gravitational Waves [Cross-Listing]

We demonstrate how to realize within supergravity a novel chaotic-type inflationary scenario driven by the radial parts of a conjugate pair of Higgs superfields causing the spontaneous breaking of a grand unified gauge symmetry at a scale assuming the value of the supersymmetric grand unification scale. The superpotential is uniquely determined at the renormalizable level by the gauge symmetry and a continuous R symmetry. We select two types of Kahler potentials, which respect these symmetries as well as an approximate shift symmetry. In particular, they include in a logarithm a dominant shift-symmetric term proportional to a parameter c- together with a small term violating this symmetry and characterized by a parameter c+. In both cases, imposing a lower bound on c-, inflation can be attained with subplanckian values of the original inflaton, while the corresponding effective theory respects perturbative unitarity for r+-=c+/c-<1. These inflationary models do not lead to overproduction of cosmic defects, are largely independent of the one-loop radiative corrections and accommodate, for natural values of r+-, observable gravitational waves consistently with all the current observational data. The inflaton mass is mostly confined in the range (3.7-8.1)x10^10 GeV.

Dark Matter and Global Symmetries [Cross-Listing]

General considerations in general relativity and quantum mechanics rule out global symmetries in the context of any consistent theory of quantum gravity. Motivated by this, we derive stringent and robust bounds from gamma-ray, X-ray, cosmic ray, neutrino and CMB data on models that invoke global symmetries to stabilize the dark matter particle. Under realistic assumptions we are able to rule out fermionic, vector, and scalar dark matter candidates across a broad mass range (keV-TeV), including the WIMP regime. We then specialize our analysis and apply our bounds to specific models such as the Two-Higgs-Doublet, Left-Right, Singlet Fermionic, Zee-Babu, 3-3-1 and Radiative See-Saw models. In the supplemental material we derive robust, updated model-independent limits on the dark matter lifetime.

Dark Matter and Global Symmetries

General considerations in general relativity and quantum mechanics rule out global symmetries in the context of any consistent theory of quantum gravity. Motivated by this, we derive stringent and robust bounds from gamma-ray, X-ray, cosmic ray, neutrino and CMB data on models that invoke global symmetries to stabilize the dark matter particle. Under realistic assumptions we are able to rule out fermionic, vector, and scalar dark matter candidates across a broad mass range (keV-TeV), including the WIMP regime. We then specialize our analysis and apply our bounds to specific models such as the Two-Higgs-Doublet, Left-Right, Singlet Fermionic, Zee-Babu, 3-3-1 and Radiative See-Saw models. In the supplemental material we derive robust, updated model-independent limits on the dark matter lifetime.

Effects of simulated cosmological magnetic fields on the galaxy population

We investigate the effects of varying the intensity of the primordial magnetic seed field on the global properties of the galaxy population in ideal MHD cosmological simulations performed with the moving-mesh code AREPO. We vary the seed field in our calculations in a range of values still compatible with the current cosmological upper limits. We show that above a critical intensity of $\simeq 10^{-9}\,{\rm G}$ the additional pressure arising from the field strongly affects the evolution of gaseous structures, leading to a suppression of the cosmic star formation history. The suppression is stronger for larger seed fields, and directly reflects into a lower galaxy number density at fixed stellar mass and a less massive stellar component at fixed virial mass at all mass scales. These signatures may be used, in addition to the existing methods, to derive tighter constraints on primordial magnetic seed field intensities.

Relaxing the limits on inflationary magnetogenesis

Inflation has long been thought as the best way of producing primordial large-scale magnetic fields. To achieve fields strong enough to seed the galactic dynamo, most of the mechanisms operate outside conventional electromagnetic theory. The latter is typically restored after the end of the de Sitter phase. Breaking away from standard electromagnetism can lead to substantially stronger magnetic fields at the end of inflation, compensating for the depletion caused by their subsequent adiabatic decay. We argue that the drastic magnetic enhancements during the de Sitter era may not be necessary because, contrary to the widespread perception, superhorizon-sized magnetic fields decay at a slower pace after inflation. The principle behind this claim is causality, which confines the post-inflationary electric currents inside the horizon. Without the currents there can be no electric-field elimination and no magnetic-flux freezing on super-Hubble lengths. There, the magnetic decay slows down, making it easier to produce primordial fields of astrophysical interest. In fact, non-conventional mechanisms of inflationary magnetogenesis that produce fields stronger than $10^{17}$ G at the end of the de Sitter expansion, could successfully seed the galactic dynamo today.

On Nonlocal Modified Gravity and Cosmology [Cross-Listing]

Despite many nice properties and numerous achievements, general relativity is not a complete theory. One of actual approaches towards more complete theory of gravity is its nonlocal modification. We present here a brief review of nonlocal gravity with its cosmological solutions. In particular, we pay special attention to two nonlocal models and their nonsingular bounce solutions for the cosmic scale factor.

On Nonlocal Modified Gravity and Cosmology [Cross-Listing]

Despite many nice properties and numerous achievements, general relativity is not a complete theory. One of actual approaches towards more complete theory of gravity is its nonlocal modification. We present here a brief review of nonlocal gravity with its cosmological solutions. In particular, we pay special attention to two nonlocal models and their nonsingular bounce solutions for the cosmic scale factor.

Teleparallel quintessence with a non-minimal coupling to a boundary term [Cross-Listing]

We propose a new model in the teleparallel framework where we consider a scalar field non-minimally coupled to both the torsion $T$ and a boundary term given by the divergence of the torsion vector $B=\frac{2}{e}\partial_\mu (eT^\mu)$. This is inspired by the relation $R=-T+B$ between the Ricci scalar of general relativity and the torsion of teleparallel gravity. This theory in suitable limits incorporates both the non-minimal coupling of a scalar field to torsion, and the non-minimal coupling of a scalar field to the Ricci scalar. We analyse the cosmology of such models, and we perform a dynamical systems analysis on the case when we have only a pure coupling to the boundary term. It is found that the system generically evolves to a late time accelerating attractor solution without requiring any fine tuning of the parameters. A dynamical crossing of the phantom barrier is also shown to be possible.

Curvature Perturbation and Domain Wall Formation with Pseudo Scaling Scalar Dynamics [Cross-Listing]

Cosmological dynamics of scalar field with a monomial potential $\phi^{n}$ with a general background equation of state is revisited. It is known that if $n$ is smaller than a critical value, the scalar field exhibits a coherent oscillation and if $n$ is larger it obeys a scaling solution without oscillation. We study in detail the case where $n$ is equal to the critical value, and find a peculiar scalar dynamics which is neither oscillating nor scaling solution, and we call it a pseudo scaling solution. We also discuss cosmological implications of a pseudo scaling scalar dynamics, such as the curvature perturbation and the domain wall problem.

Curvature Perturbation and Domain Wall Formation with Pseudo Scaling Scalar Dynamics [Cross-Listing]

Cosmological dynamics of scalar field with a monomial potential $\phi^{n}$ with a general background equation of state is revisited. It is known that if $n$ is smaller than a critical value, the scalar field exhibits a coherent oscillation and if $n$ is larger it obeys a scaling solution without oscillation. We study in detail the case where $n$ is equal to the critical value, and find a peculiar scalar dynamics which is neither oscillating nor scaling solution, and we call it a pseudo scaling solution. We also discuss cosmological implications of a pseudo scaling scalar dynamics, such as the curvature perturbation and the domain wall problem.

Scalar field cosmology modified by the Generalized Uncertainty Principle [Cross-Listing]

We consider quintessence scalar field cosmology in which the Lagrangian of the scalar field is modified by the Generalized Uncertainty Principle. We show that the perturbation terms which arise from the deformed algebra are equivalent with the existence of a second scalar field, where the two fields interact in the kinetic part. Moreover, we consider a spatially flat Friedmann-Lema\^{\i}tre-Robertson-Walker spacetime (FLRW), and we derive the gravitational field equations. We show that the modified equation of state parameter $w_{GUP}$ can cross the phantom divide line; that is $w_{GUP}<-1$. Furthermore, we derive the field equations in the dimensionless parameters, the dynamical system which arises is a singular perturbation system in which we study the existence of the fixed points in the slow manifold. Finally, we perform numerical simulations for some well known models and we show that for these models with the specific initial conditions, the parameter $w_{GUP}$ crosses the phantom barrier.

Scalar field cosmology modified by the Generalized Uncertainty Principle [Cross-Listing]

We consider quintessence scalar field cosmology in which the Lagrangian of the scalar field is modified by the Generalized Uncertainty Principle. We show that the perturbation terms which arise from the deformed algebra are equivalent with the existence of a second scalar field, where the two fields interact in the kinetic part. Moreover, we consider a spatially flat Friedmann-Lema\^{\i}tre-Robertson-Walker spacetime (FLRW), and we derive the gravitational field equations. We show that the modified equation of state parameter $w_{GUP}$ can cross the phantom divide line; that is $w_{GUP}<-1$. Furthermore, we derive the field equations in the dimensionless parameters, the dynamical system which arises is a singular perturbation system in which we study the existence of the fixed points in the slow manifold. Finally, we perform numerical simulations for some well known models and we show that for these models with the specific initial conditions, the parameter $w_{GUP}$ crosses the phantom barrier.

A coronagraphic absorbing cloud reveals the narrow-line region and extended Lyman-$\alpha$ emission of QSO J0823+0529

We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 ($z_{\rm CIV}$$\sim$3.1875), whose Broad Line Region (BLR) is partly eclipsed by a strong damped Lyman-$\alpha$ (DLA; log$N$(HI)=21.7) cloud. This allows us to study the Narrow Line Region (NLR) of the quasar and the Lyman-$\alpha$ emission from the host galaxy. Using CLOUDY models that explain the presence of strong NV and PV absorption together with the detection of SiII$^*$ and OI$^{**}$ absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 $<$ $n_{\rm H}$ $<$ 710 cm$^{-3}$ and 580 $>$ $r_0$ $>$230 pc, respectively. Sizes of the neutral($\sim$2-9pc) and highly ionized phases ($\sim$3-80pc) are consistent with the partial coverage of the CIV broad line region by the CIV absorption from the DLA (covering factor of $\sim$0.85). We show that the residuals are consistent with emission from the NLR with CIV/Lyman-$\alpha$ ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman-$\alpha$ emission up to 25kpc to the North and West directions and 15kpc to the South and East. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10kpc with emission in a wind of projected velocity $\sim$500kms$^{-1}$ which is seen up to 25kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being in-falling towards the AGN and possibly being located where accretion from cold streams ends up.

The foreground wedge and 21 cm BAO surveys

Redshifted H{\sc\,i} 21 cm emission from unresolved low-redshift large scale structure is a promising window for ground-based Baryon Acoustic Oscillations (BAO) observations. One of the major challenges for this method is separating the cosmic signal that contains the BAO from the foregrounds of Galactic and extra-Galactic origins that are stronger by many orders of magnitude than the former. The smooth frequency spectrum expected for the foregrounds would nominally contaminate only very small $k_\parallel$ modes; however the chromatic response of the telescope antenna pattern at this wavelength to the foreground introduces non-smooth structure, pervasively contaminating the cosmic signal over the physical scales of our interest. Such contamination defines a wedged volume in Fourier space around the transverse modes that is inaccessible for the cosmic signal. In this paper, we test the effect of this contaminated wedge on the future 21 cm BAO surveys using Fisher information matrix calculation. We include the signal improvement due to the BAO reconstruction technique that has been used for galaxy surveys and test the effect of this wedge on the BAO reconstruction as a function of signal to noises and incorporate the results in the Fisher matrix calculation. We find that the wedge effect expected at $z=1-2$ is very detrimental to the angular diameter distances: the errors on angular diameter distances increased by 3-4.4 times, while the errors on $H(z)$ increased by a factor of 1.5-1.6. Meanwhile the BAO reconstruction is still valuable for constraining the Hubble parameter even in the near absence of the transverse information and even in this low signal to noise regime (i.e., $S/N < 1$) of the 21 cm surveys: for $H(z)$ precision, we observed 10–40 per cent improvement depending on redshift and the noise level. (abridged).

Large-scale anomalies in the Cosmic Microwave Background as signatures of non-Gaussianity

We derive a general expression for the probability of observing deviations from statistical isotropy in the cosmic microwave background (CMB) if the primordial fluctuations are non-Gaussian and extend to superhorizon scales. The primary motivation is to properly characterize the monopole and dipole modulations of the primordial power spectrum that are generated by the coupling between superhorizon and subhorizon perturbations. Unlike previous proposals for generating the hemispherical power asymmetry, we do not assume that the power asymmetry results from a single large superhorizon mode. Instead, we extrapolate the observed power spectrum to superhorizon scales and compute the power asymmetry that would result from a specific realization of non-Gaussian perturbations on scales larger than the observable universe. Our study encompasses many of the scenarios that have been put forward as possible explanations for the CMB hemispherical power asymmetry. We confirm our analytic predictions for the probability of a given power asymmetry by comparing them to numerical realizations of CMB maps. We find that non-local models of non-Gaussianity and scale-dependent local non-Gaussianity produce scale-dependent modulations of the power spectrum, thereby potentially producing both a monopolar and a dipolar power modulation on large scales. We then provide simple examples of finding the posterior distributions for the parameters of the bispectrum from the observed monopole and dipole modulations.

Existence and disappearance of conical singularities in GLPV theories [Cross-Listing]

In a class of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, we derive both vacuum and interior Schwarzschild solutions under the condition that the derivatives of a scalar field $\phi$ with respect to the radius $r$ vanish. If the parameter $\alpha_{\rm H}$ characterizing the deviation from Horndeski theories approaches a non-zero constant at the center of a spherically symmetric body, we find that the conical singularity arises at $r=0$ with the Ricci scalar given by $R=-2\alpha_{\rm H}/r^2$. This originates from violation of the geometrical structure of four-dimensional curvature quantities. The conical singularity can disappear for the models in which the parameter $\alpha_{\rm H}$ vanishes in the limit that $r \to 0$. We propose explicit models without the conical singularity by properly designing the classical Lagrangian in such a way that the main contribution to $\alpha_{\rm H}$ comes from the field derivative $\phi’(r)$ around $r=0$. We show that the extension of covariant Galileons with a diatonic coupling allows for the recovery of general relativistic behavior inside a so-called Vainshtein radius. In this case, both the propagation of a fifth force and the deviation from Horndeski theories are suppressed outside a compact body in such a way that the model is compatible with local gravity experiments inside the solar system.

Existence and disappearance of conical singularities in GLPV theories [Cross-Listing]

In a class of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, we derive both vacuum and interior Schwarzschild solutions under the condition that the derivatives of a scalar field $\phi$ with respect to the radius $r$ vanish. If the parameter $\alpha_{\rm H}$ characterizing the deviation from Horndeski theories approaches a non-zero constant at the center of a spherically symmetric body, we find that the conical singularity arises at $r=0$ with the Ricci scalar given by $R=-2\alpha_{\rm H}/r^2$. This originates from violation of the geometrical structure of four-dimensional curvature quantities. The conical singularity can disappear for the models in which the parameter $\alpha_{\rm H}$ vanishes in the limit that $r \to 0$. We propose explicit models without the conical singularity by properly designing the classical Lagrangian in such a way that the main contribution to $\alpha_{\rm H}$ comes from the field derivative $\phi’(r)$ around $r=0$. We show that the extension of covariant Galileons with a diatonic coupling allows for the recovery of general relativistic behavior inside a so-called Vainshtein radius. In this case, both the propagation of a fifth force and the deviation from Horndeski theories are suppressed outside a compact body in such a way that the model is compatible with local gravity experiments inside the solar system.

Phases of New Physics in the CMB [Cross-Listing]

Fluctuations in the cosmic neutrino background are known to produce a phase shift in the acoustic peaks of the cosmic microwave background. It is through the sensitivity to this effect that the recent CMB data has provided a robust detection of free-streaming neutrinos. In this paper, we revisit the phase shift of the CMB anisotropy spectrum as a probe of new physics. The phase shift is particularly interesting because its physical origin is strongly constrained by the analytic properties of the Green’s function of the gravitational potential. For adiabatic fluctuations, a phase shift requires modes that propagate faster than the speed of fluctuations in the photon-baryon plasma. This possibility is realized by free-streaming relativistic particles, such as neutrinos or other forms of dark radiation. Alternatively, a phase shift can arise from isocurvature fluctuations. We present simple models to illustrate each of these effects. We then provide observational constraints from the Planck temperature and polarization data on additional forms of radiation. We also forecast the capabilities of future CMB Stage IV experiments. Whenever possible, we give analytic interpretations of our results.

Phases of New Physics in the CMB [Cross-Listing]

Fluctuations in the cosmic neutrino background are known to produce a phase shift in the acoustic peaks of the cosmic microwave background. It is through the sensitivity to this effect that the recent CMB data has provided a robust detection of free-streaming neutrinos. In this paper, we revisit the phase shift of the CMB anisotropy spectrum as a probe of new physics. The phase shift is particularly interesting because its physical origin is strongly constrained by the analytic properties of the Green’s function of the gravitational potential. For adiabatic fluctuations, a phase shift requires modes that propagate faster than the speed of fluctuations in the photon-baryon plasma. This possibility is realized by free-streaming relativistic particles, such as neutrinos or other forms of dark radiation. Alternatively, a phase shift can arise from isocurvature fluctuations. We present simple models to illustrate each of these effects. We then provide observational constraints from the Planck temperature and polarization data on additional forms of radiation. We also forecast the capabilities of future CMB Stage IV experiments. Whenever possible, we give analytic interpretations of our results.

Phases of New Physics in the CMB

Fluctuations in the cosmic neutrino background are known to produce a phase shift in the acoustic peaks of the cosmic microwave background. It is through the sensitivity to this effect that the recent CMB data has provided a robust detection of free-streaming neutrinos. In this paper, we revisit the phase shift of the CMB anisotropy spectrum as a probe of new physics. The phase shift is particularly interesting because its physical origin is strongly constrained by the analytic properties of the Green’s function of the gravitational potential. For adiabatic fluctuations, a phase shift requires modes that propagate faster than the speed of fluctuations in the photon-baryon plasma. This possibility is realized by free-streaming relativistic particles, such as neutrinos or other forms of dark radiation. Alternatively, a phase shift can arise from isocurvature fluctuations. We present simple models to illustrate each of these effects. We then provide observational constraints from the Planck temperature and polarization data on additional forms of radiation. We also forecast the capabilities of future CMB Stage IV experiments. Whenever possible, we give analytic interpretations of our results.

 

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