Recent Postings from Cosmology and Extragalactic

Negative running prevents eternal inflation

Current data from the Planck satellite and the BICEP2 telescope favor, at around the $2 \sigma$ level, negative running of the spectral index of curvature perturbations from inflation. We show that for negative running $\alpha < 0$, the curvature perturbation amplitude has a maximum on scales larger than our current horizon size. A condition for the absence of eternal inflation is that the curvature perturbation amplitude always remain below unity on superhorizon scales. For current bounds on $n_{\rm S}$ from Planck, this corresponds to an upper bound of the running $\alpha < – 4 \times 10^{-5}$, so that even tiny running of the scalar spectral index is sufficient to prevent eternal inflation from occurring, as long as the running remains negative on scales outside the horizon. In single-field inflation models, negative running is associated with a finite duration of inflation: we show that eternal inflation may not occur even in cases where inflation lasts as long as $10^4$ e-folds.

Emergent gravity, violated relativity and dark matter [Cross-Listing]

The nonlinear affine Goldstone model of the emergent gravity, built on the nonlinearly realized/hidden affine symmetry, is concisely revisited. Beyond General Relativity, the explicit violation of general invariance/relativity, under preserving general covariance, is exposed. Dependent on a nondynamical affine connection, a generally covariant second-order effective Lagrangian for metric gravity is worked out, with the general relativity violation and the gravitational dark matter serving as the signatures of emergence.

Emergent gravity, violated relativity and dark matter [Cross-Listing]

The nonlinear affine Goldstone model of the emergent gravity, built on the nonlinearly realized/hidden affine symmetry, is concisely revisited. Beyond General Relativity, the explicit violation of general invariance/relativity, under preserving general covariance, is exposed. Dependent on a nondynamical affine connection, a generally covariant second-order effective Lagrangian for metric gravity is worked out, with the general relativity violation and the gravitational dark matter serving as the signatures of emergence.

Emergent gravity, violated relativity and dark matter

The nonlinear affine Goldstone model of the emergent gravity, built on the nonlinearly realized/hidden affine symmetry, is concisely revisited. Beyond General Relativity, the explicit violation of general invariance/relativity, under preserving general covariance, is exposed. Dependent on a nondynamical affine connection, a generally covariant second-order effective Lagrangian for metric gravity is worked out, with the general relativity violation and the gravitational dark matter serving as the signatures of emergence.

The C IV Forest as a Probe of Baryon Acoustic Oscillations

In light of recent successes in measuring baryon acoustic oscillations in quasar absorption using the Lyman-alpha (Ly-alpha) transition, I explore the possibility of using the 1548 Ang transition of triply-ionized carbon (C IV) as a tracer. While the Ly-alpha forest is a more sensitive tracer of intergalactic gas, it is limited by the fact that it can only be measured in the optical window at redshifts z > 2. Quasars are challenging to identify and observe at these high-redshifts, but the C IV forest can be probed down to redshifts z = 1.3, taking full advantage of the peak in the redshift distribution of quasars that can be targeted with high efficiency. I explore the strength of the C IV absorption signal and show that the absorbing population on the red side of the Ly-alpha emission line is dominated by C IV. As a consequence, I argue that forthcoming surveys will have a sufficient increase in quasar number density to offset the lower sensitivity of the C IV forest and provide competitive precision using both the C IV autocorrelation and the C IV-quasar cross correlation at <z> = 1.6.

Extended axion electrodynamics: Anomalous dynamo-optical response induced by gravitational pp-waves

We extend the Einstein-Maxwell-axion theory including into the Lagrangian cross-terms of the dynamo-optical type, which are quadratic in the Maxwell tensor, linear in the covariant derivative of the macroscopic velocity four-vector, and linear in the pseudoscalar (axion) field or its gradient four-vector. We classify the new terms with respect to irreducible elements of the covariant derivative of the macroscopic velocity four-vector of the electromagnetically active medium: the expansion scalar, acceleration four-vector, shear and vorticity tensors. Master equations of the extended axion electrodynamics are used for the description of the response of an axionically active electrodynamic system, induced by a pp-wave gravitational background. We show that this response has a critical character, i.e., the electric and magnetic fields, dynamo-optically coupled to the axions, grow anomalously under the influence of the external pp-wave gravitational field.

Extended axion electrodynamics: Anomalous dynamo-optical response induced by gravitational pp-waves [Cross-Listing]

We extend the Einstein-Maxwell-axion theory including into the Lagrangian cross-terms of the dynamo-optical type, which are quadratic in the Maxwell tensor, linear in the covariant derivative of the macroscopic velocity four-vector, and linear in the pseudoscalar (axion) field or its gradient four-vector. We classify the new terms with respect to irreducible elements of the covariant derivative of the macroscopic velocity four-vector of the electromagnetically active medium: the expansion scalar, acceleration four-vector, shear and vorticity tensors. Master equations of the extended axion electrodynamics are used for the description of the response of an axionically active electrodynamic system, induced by a pp-wave gravitational background. We show that this response has a critical character, i.e., the electric and magnetic fields, dynamo-optically coupled to the axions, grow anomalously under the influence of the external pp-wave gravitational field.

Extended axion electrodynamics: Anomalous dynamo-optical response induced by gravitational pp-waves [Cross-Listing]

We extend the Einstein-Maxwell-axion theory including into the Lagrangian cross-terms of the dynamo-optical type, which are quadratic in the Maxwell tensor, linear in the covariant derivative of the macroscopic velocity four-vector, and linear in the pseudoscalar (axion) field or its gradient four-vector. We classify the new terms with respect to irreducible elements of the covariant derivative of the macroscopic velocity four-vector of the electromagnetically active medium: the expansion scalar, acceleration four-vector, shear and vorticity tensors. Master equations of the extended axion electrodynamics are used for the description of the response of an axionically active electrodynamic system, induced by a pp-wave gravitational background. We show that this response has a critical character, i.e., the electric and magnetic fields, dynamo-optically coupled to the axions, grow anomalously under the influence of the external pp-wave gravitational field.

Dark matter relic density in Gauss-Bonnet braneworld cosmology

The relic density of symmetric and asymmetric dark matter in the Gauss-Bonnet braneworld cosmology is investigated. The reduced expansion rate in this scenario delays particle freeze-out, leading to relic abundances which are suppressed by up to $\mathcal{O}(10^{-3})$. In this case the annihilation cross section must be reduced by up to two orders of magnitude below the canonical value $\langle\sigma v\rangle \approx 2\times 10^{-26}$ cm$^3$s$^{-1}$ to reconcile the predicted dark matter density with observation. We use the latest observational bound $\Omega_{DM}h^2 = 0.1187 \pm 0.0017$ to constrain the various model parameters and discuss the implications for direct/indirect dark matter detection experiments as well as dark matter particle models.

Robustness of $H_0$ determination at intermediate redshifts [Cross-Listing]

The most recent Hubble constant $(H_0)$ estimates from local methods ($z<<1$), $H_0=73.8\pm 2.4$ km s$^{-1}$ Mpc$^{-1}$, and the one from high redshits (Planck Collaboration 2013), $H_0=67.3\pm 1.2$ km s$^{-1}$ Mpc$^{-1}$, are discrepant at $2.4 \sigma$ confidence level. Within this context, Lima & Cunha (LC) (ApJL 781, 38, 2014) derived a new determination of $H_0$ using four cosmic probes at intermediate redshifts ($0.1<z<1.8$) based on the so-called flat $\Lambda$CDM model. They obtained $H_0=74.1\pm 2.2$ km s$^{-1}$ Mpc$^{-1}$, in full agreement with local measurements. In this letter, we explore the robustness of the LC result searching for systematic errors and its dependence from the cosmological model used. We find that the $H_0$ value from this joint analysis is very weakly dependent on the underlying cosmological model, but the morphology adopted to infer the distance to galaxy clusters changes the result sizeably, being the main source of systematic errors.

Robustness of $H_0$ determination at intermediate redshifts

The most recent Hubble constant $(H_0)$ estimates from local methods ($z<<1$), $H_0=73.8\pm 2.4$ km s$^{-1}$ Mpc$^{-1}$, and the one from high redshits (Planck Collaboration 2013), $H_0=67.3\pm 1.2$ km s$^{-1}$ Mpc$^{-1}$, are discrepant at $2.4 \sigma$ confidence level. Within this context, Lima & Cunha (LC) (ApJL 781, 38, 2014) derived a new determination of $H_0$ using four cosmic probes at intermediate redshifts ($0.1<z<1.8$) based on the so-called flat $\Lambda$CDM model. They obtained $H_0=74.1\pm 2.2$ km s$^{-1}$ Mpc$^{-1}$, in full agreement with local measurements. In this letter, we explore the robustness of the LC result searching for systematic errors and its dependence from the cosmological model used. We find that the $H_0$ value from this joint analysis is very weakly dependent on the underlying cosmological model, but the morphology adopted to infer the distance to galaxy clusters changes the result sizeably, being the main source of systematic errors.

The Epoch of Reionization Window: II. Statistical Methods for Foreground Wedge Reduction

For there to be a successful measurement of the 21 cm Epoch of Reionization (EoR) power spectrum, it is crucial that foreground contaminants be robustly suppressed. These foregrounds come from a variety of sources (such as Galactic synchrotron emission and extragalactic point sources), but almost all share the property of being spectrally smooth. When considered with the chromatic response of an interferometric measurement, spectrally smooth foregrounds contaminate a signature "wedge" region in cylindrical $k_\perp k_\parallel$ Fourier space. The complement of the foreground wedge is termed the "EoR window", and is expected to be mostly foreground-free, allowing clean measurements of the power spectrum. This paper is a sequel to a previous paper that established a rigorous mathematical framework for describing the foreground wedge and the EoR window. Here, we explore statistical methods by which the EoR window can be enlarged, thereby increasing power spectrum sensitivity. We adapt the Feldman-Kaiser-Peacock approximation (commonly used in galaxy surveys) for 21 cm cosmology, and also compare the optimal quadratic estimator to basic estimators (where Fourier modes are simply squared and binned without regard for the covariance between modes). The optimal quadratic estimator uses both spatial and spectral information to reduce errors, and (compared to the basic estimators) suppresses foregrounds by a factor of $\sim 10^5$ in power at the peripheries of the EoR window. If numerical issues can be finessed, decorrelation techniques allow the EoR window to be further enlarged, enabling measurements to be made deep within the foreground wedge. These techniques do not assume that foreground are Gaussian-distributed, and we additionally prove that a final round of foreground subtraction can be performed after decorrelation in a way that is guaranteed to have no cosmological signal loss.

Nonsingular bouncing cosmologies in light of BICEP2

We confront various nonsingular bouncing cosmologies with the recently released BICEP2 data and investigate the observational constraints on their parameter space. In particular, within the context of the effective field approach, we analyze the constraints on the matter bounce curvaton scenario with a light scalar field, and the new matter bounce cosmology model in which the universe successively experiences a period of matter contraction and an ekpyrotic phase. Additionally, we consider three nonsingular bouncing cosmologies obtained in the framework of modified gravity theories, namely the Ho\v{r}ava-Lifshitz bounce model, the $f(T)$ bounce model, and loop quantum cosmology.

Nonsingular bouncing cosmologies in light of BICEP2 [Cross-Listing]

We confront various nonsingular bouncing cosmologies with the recently released BICEP2 data and investigate the observational constraints on their parameter space. In particular, within the context of the effective field approach, we analyze the constraints on the matter bounce curvaton scenario with a light scalar field, and the new matter bounce cosmology model in which the universe successively experiences a period of matter contraction and an ekpyrotic phase. Additionally, we consider three nonsingular bouncing cosmologies obtained in the framework of modified gravity theories, namely the Ho\v{r}ava-Lifshitz bounce model, the $f(T)$ bounce model, and loop quantum cosmology.

Nonsingular bouncing cosmologies in light of BICEP2 [Cross-Listing]

We confront various nonsingular bouncing cosmologies with the recently released BICEP2 data and investigate the observational constraints on their parameter space. In particular, within the context of the effective field approach, we analyze the constraints on the matter bounce curvaton scenario with a light scalar field, and the new matter bounce cosmology model in which the universe successively experiences a period of matter contraction and an ekpyrotic phase. Additionally, we consider three nonsingular bouncing cosmologies obtained in the framework of modified gravity theories, namely the Ho\v{r}ava-Lifshitz bounce model, the $f(T)$ bounce model, and loop quantum cosmology.

One-loop Modified Gravity in de Sitter Universe, Quantum Corrected Inflation, and its Confrontation with the Planck Result

Motivated by issues on inflation, a generalized modified gravity model is investigated, where the model Lagrangian is described by a smooth function $f(R, K, \phi)$ of the Ricci scalar $R$, the kinetic term $K$ of a scalar field $\phi$. In particular, the one-loop effective action in the de Sitter background is examined on-shell as well as off-shell in the Landau gauge. In addition, the on-shell quantum equivalence of $f(R)$ gravity in the Jordan and Einstein frames is explicitly demonstrated. Furthermore, we present applications related to the stability of the de Sitter solutions and the one-loop quantum correction to inflation in quantum-corrected $R^2$ gravity. It is shown that for a certain range of parameters, the spectral index of the curvature perturbations can be consistent with the Planck analysis, but the tensor-to-scalar ratio is smaller than the minimum value within the 1 $\sigma$ error range of the BICEP2 result.

One-loop Modified Gravity in de Sitter Universe, Quantum Corrected Inflation, and its Confrontation with the Planck Result [Cross-Listing]

Motivated by issues on inflation, a generalized modified gravity model is investigated, where the model Lagrangian is described by a smooth function $f(R, K, \phi)$ of the Ricci scalar $R$, the kinetic term $K$ of a scalar field $\phi$. In particular, the one-loop effective action in the de Sitter background is examined on-shell as well as off-shell in the Landau gauge. In addition, the on-shell quantum equivalence of $f(R)$ gravity in the Jordan and Einstein frames is explicitly demonstrated. Furthermore, we present applications related to the stability of the de Sitter solutions and the one-loop quantum correction to inflation in quantum-corrected $R^2$ gravity. It is shown that for a certain range of parameters, the spectral index of the curvature perturbations can be consistent with the Planck analysis, but the tensor-to-scalar ratio is smaller than the minimum value within the 1 $\sigma$ error range of the BICEP2 result.

One-loop Modified Gravity in de Sitter Universe, Quantum Corrected Inflation, and its Confrontation with the Planck Result [Cross-Listing]

Motivated by issues on inflation, a generalized modified gravity model is investigated, where the model Lagrangian is described by a smooth function $f(R, K, \phi)$ of the Ricci scalar $R$, the kinetic term $K$ of a scalar field $\phi$. In particular, the one-loop effective action in the de Sitter background is examined on-shell as well as off-shell in the Landau gauge. In addition, the on-shell quantum equivalence of $f(R)$ gravity in the Jordan and Einstein frames is explicitly demonstrated. Furthermore, we present applications related to the stability of the de Sitter solutions and the one-loop quantum correction to inflation in quantum-corrected $R^2$ gravity. It is shown that for a certain range of parameters, the spectral index of the curvature perturbations can be consistent with the Planck analysis, but the tensor-to-scalar ratio is smaller than the minimum value within the 1 $\sigma$ error range of the BICEP2 result.

One-loop Modified Gravity in de Sitter Universe, Quantum Corrected Inflation, and its Confrontation with the Planck Result [Cross-Listing]

Motivated by issues on inflation, a generalized modified gravity model is investigated, where the model Lagrangian is described by a smooth function $f(R, K, \phi)$ of the Ricci scalar $R$, the kinetic term $K$ of a scalar field $\phi$. In particular, the one-loop effective action in the de Sitter background is examined on-shell as well as off-shell in the Landau gauge. In addition, the on-shell quantum equivalence of $f(R)$ gravity in the Jordan and Einstein frames is explicitly demonstrated. Furthermore, we present applications related to the stability of the de Sitter solutions and the one-loop quantum correction to inflation in quantum-corrected $R^2$ gravity. It is shown that for a certain range of parameters, the spectral index of the curvature perturbations can be consistent with the Planck analysis, but the tensor-to-scalar ratio is smaller than the minimum value within the 1 $\sigma$ error range of the BICEP2 result.

Quantum Tests of the Einstein Equivalence Principle with the STE-QUEST Space Mission

We present in detail the scientific objectives in fundamental physics of the Space-Time Explorer and QUantum Equivalence Space Test (STE-QUEST) space mission. STE-QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing equivalence principle tests in the quantum regime, i.e. using quantum atomic wave interferometry. Although STE-QUEST was finally not selected in early 2014 because of budgetary and technological reasons, its science case was very highly rated. Our aim is to expose that science to a large audience in order to allow future projects and proposals to take advantage of the STE-QUEST experience.

Quantum Tests of the Einstein Equivalence Principle with the STE-QUEST Space Mission [Cross-Listing]

We present in detail the scientific objectives in fundamental physics of the Space-Time Explorer and QUantum Equivalence Space Test (STE-QUEST) space mission. STE-QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing equivalence principle tests in the quantum regime, i.e. using quantum atomic wave interferometry. Although STE-QUEST was finally not selected in early 2014 because of budgetary and technological reasons, its science case was very highly rated. Our aim is to expose that science to a large audience in order to allow future projects and proposals to take advantage of the STE-QUEST experience.

Generalized Kaluza-Klein reduction and scalar-tensor theories

We investigate the generalized description of the Kaluza-Klein (KK) dimensional reduction from higher-dimensional space-time. We also explore the properties of the resultant scalar-tensor theories. We demonstrate that there exists the anti-de Sitter (AdS) background solution, and examine its stability through the analysis of the perturbations around the background AdS solution. Moreover, we derive the conditions for the dimensional reduction to successfully be executed and present the KK compactification mechanism.

Generalized Kaluza-Klein reduction and scalar-tensor theories [Cross-Listing]

We investigate the generalized description of the Kaluza-Klein (KK) dimensional reduction from higher-dimensional space-time. We also explore the properties of the resultant scalar-tensor theories. We demonstrate that there exists the anti-de Sitter (AdS) background solution, and examine its stability through the analysis of the perturbations around the background AdS solution. Moreover, we derive the conditions for the dimensional reduction to successfully be executed and present the KK compactification mechanism.

Generalized Kaluza-Klein reduction and scalar-tensor theories [Cross-Listing]

We investigate the generalized description of the Kaluza-Klein (KK) dimensional reduction from higher-dimensional space-time. We also explore the properties of the resultant scalar-tensor theories. We demonstrate that there exists the anti-de Sitter (AdS) background solution, and examine its stability through the analysis of the perturbations around the background AdS solution. Moreover, we derive the conditions for the dimensional reduction to successfully be executed and present the KK compactification mechanism.

The matrix model for dessins d'enfants [Cross-Listing]

We present the matrix models that are the generating functions for branched covers of the complex projective line ramified over $0$, $1$, and $\infty$ (Grotendieck’s dessins d’enfants) of fixed genus, degree, and the ramification profile at infinity. For general ramifications at other points, the model is the two-logarithm matrix model with the external field studied previously by one of the authors (L.Ch.) and K.Palamarchuk. It lies in the class of the generalised Kontsevich models (GKM) thus being the Kadomtsev–Petviashvili (KP) hierarchy $\tau$-function and, upon the shift of times, this model is equivalent to a Hermitian one-matrix model with a general potential whose coefficients are related to the KP times by a Miwa-type transformation. The original model therefore enjoys a topological recursion and can be solved in terms of shifted moments of the standard Hermitian one-matrix model at all genera of the topological expansion. We also derive the matrix model for clean Belyi morphisms, which turns out to be the Kontsevich–Penner model introduced by the authors and Yu. Makeenko. Its partition function is also a KP hierarchy tau function, and this model is in turn equivalent to a Hermitian one-matrix model with a general potential. Finally we prove that the generating function for general two-profile Belyi morphisms is a GKM thus proving that it is also a KP hierarchy tau function in proper times.

The TT, TB, EB and BB correlations in anisotropic inflation [Cross-Listing]

Recently the BICEP2 experiment has detected the B-mode in the CMB polarization map. The ongoing and future experiments will measure the B-mode from different sky coverage and frequency bands, with the potential to reveal non-trivial features in polarization map. In this work we study the TT, TB, EB and BB correlations associated with the B-mode polarization of CMB map in models of charged anisotropic inflation. The model contains a complex inflaton field which is charged under the $U(1)$ gauge. We calculate the statistical anisotropies generated in the power spectra of the curvature perturbation, the tensor perturbation and their cross-correlation. It is shown that the asymmetry in tensor power spectrum is a very sensitive probe of the gauge coupling. While the level of statistical anisotropy in temperature power spectrum can be small and satisfy the observational bounds, the interactions from the gauge coupling can induce large directional dependence in tensor modes. This will leave interesting anisotropic fingerprints in various correlations involving the B-mode polarization such as the TB cross-correlation which may be detected in upcoming Planck polarization data. In addition, the TT correlation receives an anisotropic contribution from the tensor sector which naturally decays after $l \gtrsim 100$. We expect that the mechanism of using tensor sector to induce asymmetry at low $l$ to be generic which can also be applied to address other low $l$ CMB anomalies.

The TT, TB, EB and BB correlations in anisotropic inflation

Recently the BICEP2 experiment has detected the B-mode in the CMB polarization map. The ongoing and future experiments will measure the B-mode from different sky coverage and frequency bands, with the potential to reveal non-trivial features in polarization map. In this work we study the TT, TB, EB and BB correlations associated with the B-mode polarization of CMB map in models of charged anisotropic inflation. The model contains a complex inflaton field which is charged under the $U(1)$ gauge. We calculate the statistical anisotropies generated in the power spectra of the curvature perturbation, the tensor perturbation and their cross-correlation. It is shown that the asymmetry in tensor power spectrum is a very sensitive probe of the gauge coupling. While the level of statistical anisotropy in temperature power spectrum can be small and satisfy the observational bounds, the interactions from the gauge coupling can induce large directional dependence in tensor modes. This will leave interesting anisotropic fingerprints in various correlations involving the B-mode polarization such as the TB cross-correlation which may be detected in upcoming Planck polarization data. In addition, the TT correlation receives an anisotropic contribution from the tensor sector which naturally decays after $l \gtrsim 100$. We expect that the mechanism of using tensor sector to induce asymmetry at low $l$ to be generic which can also be applied to address other low $l$ CMB anomalies.

The TT, TB, EB and BB correlations in anisotropic inflation [Cross-Listing]

Recently the BICEP2 experiment has detected the B-mode in the CMB polarization map. The ongoing and future experiments will measure the B-mode from different sky coverage and frequency bands, with the potential to reveal non-trivial features in polarization map. In this work we study the TT, TB, EB and BB correlations associated with the B-mode polarization of CMB map in models of charged anisotropic inflation. The model contains a complex inflaton field which is charged under the $U(1)$ gauge. We calculate the statistical anisotropies generated in the power spectra of the curvature perturbation, the tensor perturbation and their cross-correlation. It is shown that the asymmetry in tensor power spectrum is a very sensitive probe of the gauge coupling. While the level of statistical anisotropy in temperature power spectrum can be small and satisfy the observational bounds, the interactions from the gauge coupling can induce large directional dependence in tensor modes. This will leave interesting anisotropic fingerprints in various correlations involving the B-mode polarization such as the TB cross-correlation which may be detected in upcoming Planck polarization data. In addition, the TT correlation receives an anisotropic contribution from the tensor sector which naturally decays after $l \gtrsim 100$. We expect that the mechanism of using tensor sector to induce asymmetry at low $l$ to be generic which can also be applied to address other low $l$ CMB anomalies.

Cosmological perturbations in massive bigravity: I. Linear growth of structures [Cross-Listing]

The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction instead of a nonzero cosmological constant. Here the cosmological perturbations are studied in these theories. The full perturbation equations are presented in a general gauge and analyzed focusing on subhorizon scales during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. The theory predictions are confronted with observational data on both background expansion and large-scale structure, and it is found that while the models fit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments.

Cosmological perturbations in massive bigravity: I. Linear growth of structures

The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction instead of a nonzero cosmological constant. Here the cosmological perturbations are studied in these theories. The full perturbation equations are presented in a general gauge and analyzed focusing on subhorizon scales during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. The theory predictions are confronted with observational data on both background expansion and large-scale structure, and it is found that while the models fit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments.

Cosmological perturbations in massive bigravity: I. Linear growth of structures [Cross-Listing]

The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction instead of a nonzero cosmological constant. Here the cosmological perturbations are studied in these theories. The full perturbation equations are presented in a general gauge and analyzed focusing on subhorizon scales during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. The theory predictions are confronted with observational data on both background expansion and large-scale structure, and it is found that while the models fit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments.

Constraining globular cluster formation through studies of young massive clusters - II. A Single Stellar Population Young Massive Cluster in NGC 34

Currently there are two competing scenarios to explain the origin of the stellar population in globular clusters (GCs). The main difference between them is whether or not multiple events of star formation took place within GCs. In this paper we present the star formation history (SFH) of Cluster 1, a massive young cluster in NGC 34 $(\sim10^7\mbox{ M}_\odot)$. We use DynBaS, a spectrum fitting algorithm, to retrieve the SFH and find that Cluster 1 is consistent with a single stellar population of solar metallicity with an age of $100\pm30$ Myr and a mass of $1.9\pm0.4\times10^7\mbox{ M}_\odot$. These results are in conflict with the expectations/predictions of the scenarios that invoke extended or multiple episodes within 30–100 Myr of the initial star-formation burst in young massive clusters.

Loop quantum cosmology of a radiation-dominated flat FLRW universe [Cross-Listing]

We study the loop quantum cosmology of a flat Friedmann-Lemaitre-Robertson-Walker space-time with a Maxwell field. We show that many of the qualitative properties derived for the case of a massless scalar field also hold for a Maxwell field. In particular, the big-bang singularity is replaced by a quantum bounce, and the operator corresponding to the matter energy density is bounded above by the same critical energy density. We also numerically study the evolution of wave functions that are sharply peaked in the low energy regime, and derive effective equations which very closely approximate the full quantum dynamics of sharply peaked states at all times, including the near-bounce epoch.

Loop quantum cosmology of a radiation-dominated flat FLRW universe

We study the loop quantum cosmology of a flat Friedmann-Lemaitre-Robertson-Walker space-time with a Maxwell field. We show that many of the qualitative properties derived for the case of a massless scalar field also hold for a Maxwell field. In particular, the big-bang singularity is replaced by a quantum bounce, and the operator corresponding to the matter energy density is bounded above by the same critical energy density. We also numerically study the evolution of wave functions that are sharply peaked in the low energy regime, and derive effective equations which very closely approximate the full quantum dynamics of sharply peaked states at all times, including the near-bounce epoch.

Loop quantum cosmology of a radiation-dominated flat FLRW universe [Cross-Listing]

We study the loop quantum cosmology of a flat Friedmann-Lemaitre-Robertson-Walker space-time with a Maxwell field. We show that many of the qualitative properties derived for the case of a massless scalar field also hold for a Maxwell field. In particular, the big-bang singularity is replaced by a quantum bounce, and the operator corresponding to the matter energy density is bounded above by the same critical energy density. We also numerically study the evolution of wave functions that are sharply peaked in the low energy regime, and derive effective equations which very closely approximate the full quantum dynamics of sharply peaked states at all times, including the near-bounce epoch.

The inflation point in U(1)$_{de}$ hilltop potential assisted by chaoton, BICEP2 data, and trans-Planckian decay constant

The recent BICEP2 report on the CMB B-mode polarization hints an early Universe energy density at the GUT scale. We add a new `chaoton’ term to our recently proposed hilltop potential to have a large tensor mode fluctuation. The chaoton field slides down from the hilltop when the inflaton field value is small so that an enough e-folding is possible. We also comment how the trans-Planckian decay constant is obtained from some discrete symmetries of ultra-violet completed models.

The inflation point in U(1)$_{de}$ hilltop potential assisted by chaoton, BICEP2 data, and trans-Planckian decay constant [Cross-Listing]

The recent BICEP2 report on the CMB B-mode polarization hints an early Universe energy density at the GUT scale. We add a new `chaoton’ term to our recently proposed hilltop potential to have a large tensor mode fluctuation. The chaoton field slides down from the hilltop when the inflaton field value is small so that an enough e-folding is possible. We also comment how the trans-Planckian decay constant is obtained from some discrete symmetries of ultra-violet completed models.

Probing Big Bounce with Dark Matter [Replacement]

We investigate the production of dark matter in a generic bouncing universe framework. Our result shows that, if the future-experimentally-measured cross section and mass of dark matter particle satisfy the cosmological constraint, $\langle \sigma v\rangle m_\chi^2 < 1.82\times 10^{-26}$, it becomes a strong indication that our universe went through a Big Bounce—instead of the inflationary phase as postulated in Standard Big Bang Cosmology—at the early stage of the cosmological evolution.

Probing Big Bounce with Dark Matter

We investigate the production of dark matter in a generic bouncing universe framework. Our result shows that, if the future-experimentally-measured cross section and mass of dark matter particle satisfy the cosmological constraint, $\langle \sigma v\rangle m_\chi^2 < 1.82\times 10^{-26}$, it becomes a strong indication that our universe went through a Big Bounce—instead of the inflationary phase as postulated in Standard Big Bang Cosmology—at the early stage of the cosmological evolution.

Faraday scaling and the Bicep2 observations

As repeatedly speculated in the past, the linear polarization of the Cosmic Microwave Background can be rotated via the Faraday effect. An economic explanation of the recent Bicep2 observations, not relying on long-wavelength tensor modes of the geometry, would stipulate that the detected B mode comes exclusively from a Faraday rotated E mode polarization. We show hereunder that this interpretation is ruled out by the existing upper limits on the B mode polarization obtained by independent experiments at observational frequencies much lower than the operating frequency of the Bicep2 experiment. We then derive the fraction of the observed B mode polarization ascribable to the Faraday effect and suggest a dedicated experimental strategy for its detection.

Faraday scaling and the Bicep2 observations [Cross-Listing]

As repeatedly speculated in the past, the linear polarization of the Cosmic Microwave Background can be rotated via the Faraday effect. An economic explanation of the recent Bicep2 observations, not relying on long-wavelength tensor modes of the geometry, would stipulate that the detected B mode comes exclusively from a Faraday rotated E mode polarization. We show hereunder that this interpretation is ruled out by the existing upper limits on the B mode polarization obtained by independent experiments at observational frequencies much lower than the operating frequency of the Bicep2 experiment. We then derive the fraction of the observed B mode polarization ascribable to the Faraday effect and suggest a dedicated experimental strategy for its detection.

Faraday scaling and the Bicep2 observations [Cross-Listing]

As repeatedly speculated in the past, the linear polarization of the Cosmic Microwave Background can be rotated via the Faraday effect. An economic explanation of the recent Bicep2 observations, not relying on long-wavelength tensor modes of the geometry, would stipulate that the detected B mode comes exclusively from a Faraday rotated E mode polarization. We show hereunder that this interpretation is ruled out by the existing upper limits on the B mode polarization obtained by independent experiments at observational frequencies much lower than the operating frequency of the Bicep2 experiment. We then derive the fraction of the observed B mode polarization ascribable to the Faraday effect and suggest a dedicated experimental strategy for its detection.

Faraday scaling and the Bicep2 observations [Cross-Listing]

As repeatedly speculated in the past, the linear polarization of the Cosmic Microwave Background can be rotated via the Faraday effect. An economic explanation of the recent Bicep2 observations, not relying on long-wavelength tensor modes of the geometry, would stipulate that the detected B mode comes exclusively from a Faraday rotated E mode polarization. We show hereunder that this interpretation is ruled out by the existing upper limits on the B mode polarization obtained by independent experiments at observational frequencies much lower than the operating frequency of the Bicep2 experiment. We then derive the fraction of the observed B mode polarization ascribable to the Faraday effect and suggest a dedicated experimental strategy for its detection.

Large-Scale Structure Formation: from the first non-linear objects to massive galaxy clusters

The large-scale structure of the Universe formed from initially small perturbations in the cosmic density field, leading to galaxy clusters with up to 10^15 Msun at the present day. Here, we review the formation of structures in the Universe, considering the first primordial galaxies and the most massive galaxy clusters as extreme cases of structure formation where fundamental processes such as gravity, turbulence, cooling and feedback are particularly relevant. The first non-linear objects in the Universe formed in dark matter halos with 10^5-10^8 Msun at redshifts 10-30, leading to the first stars and massive black holes. At later stages, larger scales became non-linear, leading to the formation of galaxy clusters, the most massive objects in the Universe. We describe here their formation via gravitational processes, including the self-similar scaling relations, as well as the observed deviations from such self-similarity and the related non-gravitational physics (cooling, stellar feedback, AGN). While on intermediate cluster scales the self-similar model is in good agreement with the observations, deviations from such self-similarity are apparent in the core regions, where numerical simulations do not reproduce the current observational results. The latter indicates that the interaction of different feedback processes may not be correctly accounted for in current simulations. Both in the most massive clusters of galaxies as well as during the formation of the first objects in the Universe, turbulent structures and shock waves appear to be common, suggesting them to be ubiquitous in the non-linear regime.

On Binary Driven Hypernovae and their nested late X-ray emission

Context: The induced gravitational collapse (IGC) paradigm addresses the very energetic (10^{52}-10^{54}erg) long gamma-ray bursts (GRBs) associated to supernovae (SNe). In alternative to the traditional "collapsar" model, an evolved FeCO core with a companion neutron star (NS) in a tight binary system is considered as progenitor. This special class of sources, here named "binary driven hypernovae" (BdHNe), presents a composite sequence made by four different episodes [...]. Aims: a) To compare and contrast the steep decay, the plateau and the power-law decay of the X-ray luminosities of three selected BdHNe [...]; b) to explain the different sizes and Lorentz factors of the emitting regions of the four Episodes, [...]; c) to evidence the possible role of r-process, originating in the binary system of the progenitor. Methods: We compare and contrast the late X-ray luminosity of the above three BdHNe. We examine correlations between the time at the starting point of the constant late power-law decay, t^*_a, the average prompt luminosity, <L_{iso}>, and the luminosity at the end of the plateau, L_a. We analyze a thermal emission (~0.97-0.29 keV), observed during the X-ray steep decay phase of GRB 090618. Results: The late X-ray luminosities of the three BdHNe [...] evidence a precisely constrained "nested" structure [...]. Conclusions: We confirm a constant slope power-law behavior for the late X-ray luminosity in the source rest-frame, which may lead to a new distance indicator for BdHNe. These results, as well as the emitter size and Lorentz factor, appear to be inconsistent with the traditional afterglow model based on synchrotron emission from an ultra-relativistic [...] collimated jet outflow. We argue, instead, the possible role of r-process, originating in the binary system, to power the mildly relativistic X-ray source.

A particle dark matter footprint on the first generation of stars

Dark matter particles with properties identical to dark matter candidates that are hinted at by several international collaborations dedicated to experimental detection of dark matter (DAMA, COGENT, CRESST and CDMS-II, although not, most notably, by LUX), and which also have a dark matter asymmetry identical to the observed baryon asymmetry (Planck and Wilkinson Microwave Anisotropy Probe), may produce a significant impact on the evolution of the first generation of low-metallicity stars. The lifetimes of these stars in different phases of stellar evolution are significantly extended, namely, in the pre-main sequence, main sequence, and red giant phases. In particular, intermediate-mass stars in the red giant phase experience significant changes in their luminosity and chemical composition. The annihilations of dark matter particles affect the interior of the star in such a way that the $3\alpha-$reaction becomes less efficient in the production of carbon and oxygen. This dark matter effect contradicts the excess of carbon and other metals observed today in stars of low mass and low metallicity. Hence, we can impose an upper limit on the dark matter halo density, and therefore on the redshift, at which the first generation of low-metallicity stars formed.

A particle dark matter footprint on the first generation of stars [Cross-Listing]

Dark matter particles with properties identical to dark matter candidates that are hinted at by several international collaborations dedicated to experimental detection of dark matter (DAMA, COGENT, CRESST and CDMS-II, although not, most notably, by LUX), and which also have a dark matter asymmetry identical to the observed baryon asymmetry (Planck and Wilkinson Microwave Anisotropy Probe), may produce a significant impact on the evolution of the first generation of low-metallicity stars. The lifetimes of these stars in different phases of stellar evolution are significantly extended, namely, in the pre-main sequence, main sequence, and red giant phases. In particular, intermediate-mass stars in the red giant phase experience significant changes in their luminosity and chemical composition. The annihilations of dark matter particles affect the interior of the star in such a way that the $3\alpha-$reaction becomes less efficient in the production of carbon and oxygen. This dark matter effect contradicts the excess of carbon and other metals observed today in stars of low mass and low metallicity. Hence, we can impose an upper limit on the dark matter halo density, and therefore on the redshift, at which the first generation of low-metallicity stars formed.

A particle dark matter footprint on the first generation of stars [Cross-Listing]

Dark matter particles with properties identical to dark matter candidates that are hinted at by several international collaborations dedicated to experimental detection of dark matter (DAMA, COGENT, CRESST and CDMS-II, although not, most notably, by LUX), and which also have a dark matter asymmetry identical to the observed baryon asymmetry (Planck and Wilkinson Microwave Anisotropy Probe), may produce a significant impact on the evolution of the first generation of low-metallicity stars. The lifetimes of these stars in different phases of stellar evolution are significantly extended, namely, in the pre-main sequence, main sequence, and red giant phases. In particular, intermediate-mass stars in the red giant phase experience significant changes in their luminosity and chemical composition. The annihilations of dark matter particles affect the interior of the star in such a way that the $3\alpha-$reaction becomes less efficient in the production of carbon and oxygen. This dark matter effect contradicts the excess of carbon and other metals observed today in stars of low mass and low metallicity. Hence, we can impose an upper limit on the dark matter halo density, and therefore on the redshift, at which the first generation of low-metallicity stars formed.

String theoretic QCD axions in the light of PLANCK and BICEP2

The QCD axion solving the strong CP problem may originate from antisymmetric tensor gauge fields in compactified string theory, with a decay constant around the GUT scale. Such possibility appears to be ruled out now by the detection of tensor modes by BICEP2 and the PLANCK constraints on isocurvature density perturbations. A more interesting and still viable possibility is that the string theoretic QCD axion is charged under an anomalous U(1)_A gauge symmetry. In such case, the axion decay constant can be much lower than the GUT scale if moduli are stabilized near the point of vanishing Fayet-Illiopoulos term, and U(1)_A-charged matter fields get a vacuum value far below the GUT scale due to a tachyonic SUSY breaking scalar mass. We examine the symmetry breaking pattern of such models during the inflationary epoch with the Hubble expansion rate 10^{14} GeV, and identify the range of the QCD axion decay constant, as well as the corresponding relic axion abundance, consistent with known cosmological constraints. In addition to the case that the PQ symmetry is restored during inflation, there are other viable scenarios, including that the PQ symmetry is broken during inflation at high scales around 10^{16}-10^{17} GeV due to a large Hubble-induced tachyonic scalar mass from the U(1)_A D-term, while the present axion scale is in the range 10^{9}-5\times 10^{13} GeV, where the present value larger than 10^{12} GeV requires a fine-tuning of the axion misalignment angle. We also discuss the implications of our results for the size of SUSY breaking soft masses.

String theoretic QCD axions in the light of PLANCK and BICEP2 [Cross-Listing]

The QCD axion solving the strong CP problem may originate from antisymmetric tensor gauge fields in compactified string theory, with a decay constant around the GUT scale. Such possibility appears to be ruled out now by the detection of tensor modes by BICEP2 and the PLANCK constraints on isocurvature density perturbations. A more interesting and still viable possibility is that the string theoretic QCD axion is charged under an anomalous U(1)_A gauge symmetry. In such case, the axion decay constant can be much lower than the GUT scale if moduli are stabilized near the point of vanishing Fayet-Illiopoulos term, and U(1)_A-charged matter fields get a vacuum value far below the GUT scale due to a tachyonic SUSY breaking scalar mass. We examine the symmetry breaking pattern of such models during the inflationary epoch with the Hubble expansion rate 10^{14} GeV, and identify the range of the QCD axion decay constant, as well as the corresponding relic axion abundance, consistent with known cosmological constraints. In addition to the case that the PQ symmetry is restored during inflation, there are other viable scenarios, including that the PQ symmetry is broken during inflation at high scales around 10^{16}-10^{17} GeV due to a large Hubble-induced tachyonic scalar mass from the U(1)_A D-term, while the present axion scale is in the range 10^{9}-5\times 10^{13} GeV, where the present value larger than 10^{12} GeV requires a fine-tuning of the axion misalignment angle. We also discuss the implications of our results for the size of SUSY breaking soft masses.

 

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