Posts Tagged upper bound

Recent Postings from upper bound

The LHC data and an upper bound for the inelastic diffraction

We comment on the status of the Pumplin bound for the inelastic diffraction in the light of the recent LHC data for elastic scattering

Bounds on Invisible Higgs boson Decays from $t\bar{t}H$ Production

We present an upper bound on the branching fraction of the Higgs boson to invisible particles, by recasting a CMS search for stop quarks decaying to $t\bar{t}+\missET$. The observed (expected) bound, BF($H\rightarrow$inv.$)<0. 40 (0.65)$ at 95\% CL, is the strongest direct limit to date, benefiting from a downward fluctuation in the CMS data in that channel. In addition, we combine this new constraint with existing published constraints to give an observed (expected) bound of BF($H\rightarrow$inv.$)<0. 40 (0.40)$ at 95\% CL, and show some of the implications for theories of dark matter which communicate through the Higgs portal.

The end of the MACHO era- revisited: new limits on MACHO masses from halo wide binaries

In order to determine an upper bound for the mass of the massive compact halo objets (MACHOs) we use the halo binaries contained in a recent catalog (Allen \& Monroy-Rodr\’{\i}guez 2013). To dynamically model their interactions with massive perturbers a Monte Carlo simulation is conducted, using an impulsive approximation method and assuming a galactic halo constituted by massive particles of a characteristic mass. The results of such simulations are compared with several subsamples of our improved catalog of candidate halo wide binaries. In accordance with Quinn et al. (2009) we also find our results to be very sensitive to the widest binaries. However, our larger sample, together with the fact that we can obtain galactic orbits for 150 of our systems, allows a more reliable estimate of the maximum MACHO mass than that obtained previously. If we employ the entire sample of 211 candidate halo stars we obtain an upper limit of $112 M_\sun$. However, using the 150 binaries in our catalog with computed galactic orbits we are able to refine our fitting criteria. Thus, for the 100 most halo-like binaries we obtain a maximum MACHO mass of $21-68 M_\sun$. Furthermore, we can estimate the dynamical effects of the galactic disk using binary samples that spend progressively shorter times within the disk. By extrapolating the limits obtained for our most reliable -albeit smallest- sample we find that as the time spent within the disk tends to zero the upper bound of the MACHO mass tends to less than $5 M_\sun$. The non-uniform density of the halo has also been taken into account, but the limit obtained, less than $5 M_\sun$, does not differ much from the previous one. Together with microlensing studies that provide lower limits on the MACHO mass, our results essentially exclude the existence of such objects in the galactic halo.

Perturbative $\lambda$-Supersymmetry and Small $\kappa$-Phenomenology

For the minimal $\lambda$-supersymmetry, it stays perturbative to GUT scale if $\lambda \leq 0.7$. This upper bound can be relaxed if one either takes the criteria for non-perturbation when coupling closes to $\sim 4\pi$ or allows new fields at intermediate scale. It is shown that a simple $U(1)_X$ gauge sector with spontaneously broken scale $\sim10$ TeV improves the bound as $\lambda\leq1.2$ instead. This deviation can induce significant effects on Higgs physics such as decreasing fine tuning involving Higgs mass, as well as on small $\kappa$-phenomenology, the latter of which will be revised for $\lambda$ in this new range.

Perturbative $\lambda$-Supersymmetry and Small $\kappa$-Phenomenology [Replacement]

For the minimal $\lambda$-supersymmetry, it stays perturbative to GUT scale if $\lambda \leq 0.7$. This upper bound can be relaxed if one either takes the criteria for non-perturbation when coupling closes to $\sim 4\pi$ or allows new fields at intermediate scale. It is shown that a simple $U(1)_X$ gauge sector with spontaneously broken scale $\sim10$ TeV improves the bound as $\lambda\leq1.2$ instead. This deviation can induce significant effects on Higgs physics such as decreasing fine tuning involving Higgs mass, as well as on small $\kappa$-phenomenology, the latter of which will be revised for $\lambda$ in this new range.

Upper Bound on the Tensor-to-Scalar Ratio in GUT-Scale Supersymmetric Hybrid Inflation [Replacement]

We explore the upper bound on the tensor-to-scalar ratio $r$ in supersymmetric (F-term) hybrid inflation models with the gauge symmetry breaking scale set equal to the value $2.86\cdot10^{16} {\rm GeV}$, as dictated by the unification of the MSSM gauge couplings. We employ a unique renormalizable superpotential and a quasi-canonical K\"ahler potential, and the scalar spectral index $n_s$ is required to lie within the two-sigma interval from the central value found by the Planck satellite. In a sizable region of the parameter space the potential along the inflationary trajectory is a monotonically increasing function of the inflaton, and for this case, $r\lesssim2.9\cdot10^{-4}$, while the spectral index running, $|dn_{\rm s}/d\ln k|$, can be as large as $0.01$. Ignoring higher order terms which ensure the boundedness of the potential for large values of the inflaton, the upper bound on $r$ is significantly larger, of order $0.01$, for subplanckian values of the inflaton, and $|dn_{\rm s}/d\ln k|\simeq0.006$.

Upper Bound on the Tensor-to-Scalar Ratio in GUT-Scale Supersymmetric Hybrid Inflation [Replacement]

We explore the upper bound on the tensor-to-scalar ratio $r$ in supersymmetric (F-term) hybrid inflation models with the gauge symmetry breaking scale set equal to the value $2.86\cdot10^{16} {\rm GeV}$, as dictated by the unification of the MSSM gauge couplings. We employ a unique renormalizable superpotential and a quasi-canonical K\"ahler potential, and the scalar spectral index $n_s$ is required to lie within the two-sigma interval from the central value found by the Planck satellite. In a sizable region of the parameter space the potential along the inflationary trajectory is a monotonically increasing function of the inflaton, and for this case, $r\lesssim2.9\cdot10^{-4}$, while the spectral index running, $|dn_{\rm s}/d\ln k|$, can be as large as $0.01$. Ignoring higher order terms which ensure the boundedness of the potential for large values of the inflaton, the upper bound on $r$ is significantly larger, of order $0.01$, for subplanckian values of the inflaton, and $|dn_{\rm s}/d\ln k|\simeq0.006$.

Upper Bound on the Tensor-to-Scalar Ratio in GUT-Scale Supersymmetric Hybrid Inflation [Cross-Listing]

We explore the upper bound on the tensor-to-scalar ratio $r$ in supersymmetric (F-term) hybrid inflation models with the gauge symmetry breaking scale set equal to the value $2.86\cdot10^{16} {\rm GeV}$, as dictated by the unification of the MSSM gauge couplings. We employ a unique renormalizable superpotential and a quasi-canonical K\"ahler potential, and the scalar spectral index $n_s$ is required to lie within the two-sigma interval from the central value found by the Planck satellite. In a sizable region of the parameter space the potential along the inflationary trajectory is a monotonically increasing function of the inflaton, and for this case, $r\lesssim2.9\cdot10^{-4}$, while the spectral index running, $|dn_{\rm s}/d\ln k|$, can be as large as $0.01$. Ignoring higher order terms which ensure the boundedness of the potential for large values of the inflaton, the upper bound on $r$ is significantly larger, of order $0.01$, for subplanckian values of the inflaton, and $|dn_{\rm s}/d\ln k|\simeq0.006$.

Upper Bound on the Tensor-to-Scalar Ratio in GUT-Scale Supersymmetric Hybrid Inflation

We explore the upper bound on the tensor-to-scalar ratio $r$ in supersymmetric (F-term) hybrid inflation models with the gauge symmetry breaking scale set equal to the value $2.86\cdot10^{16} {\rm GeV}$, as dictated by the unification of the MSSM gauge couplings. We employ a unique renormalizable superpotential and a quasi-canonical K\"ahler potential, and the scalar spectral index $n_s$ is required to lie within the two-sigma interval from the central value found by the Planck satellite. In a sizable region of the parameter space the potential along the inflationary trajectory is a monotonically increasing function of the inflaton, and for this case, $r\lesssim2.9\cdot10^{-4}$, while the spectral index running, $|dn_{\rm s}/d\ln k|$, can be as large as $0.01$. Ignoring higher order terms which ensure the boundedness of the potential for large values of the inflaton, the upper bound on $r$ is significantly larger, of order $0.01$, for subplanckian values of the inflaton, and $|dn_{\rm s}/d\ln k|\simeq0.006$.

Upper Bound on the First Star Formation History

Our understanding of the nature of the extragalactic background light (EBL) has improved with the recent development of gamma-ray observation techniques. An open subject in the context of the EBL is the reionization epoch, which is an important probe of the formation history of first stars, the so-called Population III (Pop III) stars. Although the mechanisms for the formation of Pop III stars are rather well understood on theoretical grounds, their formation history is still veiled in mystery because of their faintness. To shed light into this matter, we study jointly the gamma-ray opacity of distant objects and the reionization constraints from studies of intergalactic gas. By combining these studies, we obtain a sensitive upper bound on the Pop III star formation rate density as $\dot\rho_{*}(z)<0.01[(1+z)/{(1+7.0)}]^{3.4}({f_{\rm esc}}/{0.2})^{-1}({C}/{3.0})\ {\rm M}_{\odot} {\rm yr}^{-1}\ {\rm Mpc}^{-3}$ at $z\ge7$, where $f_{\rm esc}$ and $C$ are the escape fraction of ionizing photons from galaxies and the clumping factor of the intergalactic hydrogen gas. This limit is a $\sim10$ times tighter constraint compared with previous studies that take into account gamma-ray opacity constraints only. Even if we do not include the current gamma-ray constraints, the results do not change. This is because the detected gamma-ray sources are still at $z\le4.35$ where the reionization has already finished.

Bounds on Operator Dimensions in 2D Conformal Field Theories [Replacement]

We extend the work of Hellerman (arxiv:0902.2790) to derive an upper bound on the conformal dimension $\Delta_2$ of the next-to-lowest nontrival primary operator in unitary two-dimensional conformal field theories without chiral primary operators. The bound we find is of the same form as found for $\Delta_1$: $\Delta_2 \leq c_{tot}/12 + O(1)$. We find a similar bound on the conformal dimension $\Delta_3$, and present a method for deriving bounds on $\Delta_n$ for any $n$, under slightly modified assumptions. For asymptotically large $c_{tot}$ and fixed $n$, we show that $\Delta_n \leq \frac{c_{tot}}{12}+O(1)$. We conclude with a brief discussion of the gravitational implications of these results.

A First Experimental Limit on In-matter Torsion from Neutron Spin Rotation in Liquid He-4 [Replacement]

We report the first experimental upper bound to our knowledge on possible in-matter torsion interactions of the neutron from a recent search for parity violation in neutron spin rotation in liquid He-4. Our experiment constrains a coefficient $\zeta$ consisting of a linear combination of parameters involving the time components of the torsion fields $T^\mu$ and $A^\mu$ from the nucleons and electrons in helium which violates parity. We report an upper bound of $|\zeta|<5.4×10^{-16}$ GeV at 68% confidence level and indicate other physical processes that could be analyzed to constrain in-matter torsion.

A First Experimental Limit on In-matter Torsion from Neutron Spin Rotation in Liquid He-4 [Replacement]

We report the first experimental upper bound to our knowledge on possible in-matter torsion interactions of the neutron from a recent search for parity violation in neutron spin rotation in liquid He-4. Our experiment constrains a coefficient $\zeta$ consisting of a linear combination of parameters involving the time components of the torsion fields $T^\mu$ and $A^\mu$ from the nucleons and electrons in helium which violates parity. We report an upper bound of $|\zeta|<5.4×10^{-16}$ GeV at 68% confidence level and indicate other physical processes that could be analyzed to constrain in-matter torsion.

A First Experimental Limit on In-matter Torsion from Neutron Spin Rotation in Liquid He-4 [Replacement]

We report the first experimental upper bound to our knowledge on possible in-matter torsion interactions of the neutron from a recent search for parity violation in neutron spin rotation in liquid He-4. Our experiment constrains a coefficient $\zeta$ consisting of a linear combination of parameters involving the time components of the torsion fields $T^\mu$ and $A^\mu$ from the nucleons and electrons in helium which violates parity. We report an upper bound of $|\zeta|<5.4×10^{-16}$ GeV at 68% confidence level and indicate other physical processes that could be analyzed to constrain in-matter torsion.

Constraints on the conservation-law/preferred-frame $\alpha_3$ parameter from orbital motions [Cross-Listing]

We analytically calculate some orbital effects induced by the Lorentz-invariance/momentum-conservation PPN parameter $\alpha_3$ in a gravitationally bound binary system made of a compact primary orbited by a test particle. We neither restrict ourselves to any particular orbital configuration nor to specific orientations of the primary’s spin axis. We use our results to put constraints on $|\alpha_3|$ in the weak-field regime by using the latest data from Solar System planetary dynamics. From the supplementary perihelion precessions determined with the EPM2011 ephemerides, we preliminarily infer $|\alpha_3|<= 9 x 10^{-11}$, which is about 3 orders of magnitude better than the previous weak-field constraints existing in the literature. The wide pulsar-white dwarf binary PSR J0407+1607 yields an upper bound on the strong-field version of the Lorentz-invariance/momentum-conservation PPN parameter ranging from 6 x $10^{-18}$ up to to 9 x $10^{-13}$ depending on the unknown values of the pulsar’s spin axis orientation and of the orbital node and inclination. We do not recur to statistical arguments involving more than one pulsar.

Constraints on the conservation-law/preferred-frame $\alpha_3$ parameter from orbital motions

We analytically calculate some orbital effects induced by the Lorentz-invariance/momentum-conservation PPN parameter $\alpha_3$ in a gravitationally bound binary system made of a compact primary orbited by a test particle. We neither restrict ourselves to any particular orbital configuration nor to specific orientations of the primary’s spin axis. We use our results to put constraints on $|\alpha_3|$ in the weak-field regime by using the latest data from Solar System planetary dynamics. From the supplementary perihelion precessions determined with the EPM2011 ephemerides, we preliminarily infer $|\alpha_3|<= 9 x 10^{-11}$, which is about 3 orders of magnitude better than the previous weak-field constraints existing in the literature. The wide pulsar-white dwarf binary PSR J0407+1607 yields an upper bound on the strong-field version of the Lorentz-invariance/momentum-conservation PPN parameter ranging from 6 x $10^{-18}$ up to to 9 x $10^{-13}$ depending on the unknown values of the pulsar’s spin axis orientation and of the orbital node and inclination. We do not recur to statistical arguments involving more than one pulsar.

Spectral Distortion in a Radially Inhomogeneous Cosmology

The spectral distortion of the cosmic microwave background blackbody spectrum in a radially inhomogeneous spacetime, designed to exactly reproduce a LambdaCDM expansion history along the past light cone, is shown to exceed the upper bound established by COBE-FIRAS by a factor of approximately 3000. This simple observational test helps uncover a slew of pathological features that lie hidden inside the past light cone, including a radially contracting phase at decoupling and, if followed to its logical extreme, a naked singularity at the radially inhomogeneous Big Bang.

Particle Production during Inflation in Light of PLANCK [Cross-Listing]

We consider trapped inflation in a higher dimensional field space: particle production at a dense distribution of extra species points leads to a terminal velocity at which inflation can be driven in steep potentials. We compute an additional, nearly scale invariant contribution to the power-spectrum, caused by back-scattering of the continuously produced particles. Since this contribution has a blue tilt, it has to be sub-dominant, leading to an upper bound on the coupling constant between the inflatons and the extra species particles. We comment on the allowed parameter space, which remains relatively broad. We further show that the currently observed red spectrum is consistent with inflation driven at the terminal velocity, while the need for functional fine tuning (the eta-problem) is reduced. A tensor to scalar ratio of r = 4 (1-n_s) is a firm prediction, which is in tension with current Planck results. An absence of gravitational waves at this level would rule out trapped inflation of this type, and limits the presence of extra species points during inflation.

Particle Production during Inflation in Light of PLANCK

We consider trapped inflation in a higher dimensional field space: particle production at a dense distribution of extra species points leads to a terminal velocity at which inflation can be driven in steep potentials. We compute an additional, nearly scale invariant contribution to the power-spectrum, caused by back-scattering of the continuously produced particles. Since this contribution has a blue tilt, it has to be sub-dominant, leading to an upper bound on the coupling constant between the inflatons and the extra species particles. We comment on the allowed parameter space, which remains relatively broad. We further show that the currently observed red spectrum is consistent with inflation driven at the terminal velocity, while the need for functional fine tuning (the eta-problem) is reduced. A tensor to scalar ratio of r = 4 (1-n_s) is a firm prediction, which is in tension with current Planck results. An absence of gravitational waves at this level would rule out trapped inflation of this type, and limits the presence of extra species points during inflation.

Constraining Primordial Magnetic Fields by CMB Photon-Graviton Conversion

We revisit the method of using the photon-graviton conversion mechanism in the presence of the external magnetic field to probe small-scale primordial magnetic fields that may exist between the last scattering surface and present. Specifically, we investigate impacts on the conversion efficiency due to the presence of matter, including the plasma collective effect and the atomic polarizability. In general, these effects tend to reduce the conversion probability. Under this more realistic picture and based on the precision of COBE’s measurement of CMB (cosmic microwave background) blackbody spectrum, we find an upper bound for the primordial magnetic field strength, B < 30G, at the time of recombination. Although at present the bound based on the photon-graviton conversion mechanism is not as tight as that obtained by the direct use of CMB temperature anisotropy, it nevertheless provides an important independent constraint on primordial magnetic fields and at epochs in addition to the recombination. The bound can be significantly improved if the CMB blackbody spectrum measurement becomes more precise in future experiments such as PIXIE.

Constraining cosmic string parameters with curl mode of CMB lensing

We present constraints on a cosmic string network with a measurement of weak gravitational lensing from CMB temperature map. The cosmic string network between observer and last scattering surface of CMB photons generates vector and/or tensor metric perturbations, and the deflection of CMB photons by these gravitational fields has curl mode which is not produced by the scalar metric perturbations. To constrain cosmic string parameters, we use the power spectrum of curl mode obtained from Planck, and also, as an independent data set, from Atacama Cosmology Telescope (ACT) 2008 season data. Based on the curl mode power spectrum, we constrain the string tension, G\mu, and the reconnection probability, P. Assuming P=1, the upper bound on tension is G\mu =6.6\times 10^{-5} with 2\sigma, using curl mode from Planck, which is weaker than that from the small-scale temperature power spectrum. For small values of P, however, the constraint from curl mode becomes tighter compared to that from temperature power spectrum. For P \lsim 10^{-2}, we obtain the constraint on the combination of the string parameters as G\mu P^{-1} \leq 3.4 \times 10^{-5} at more than 2\sigma.

Cosmic Bandits: Exploration versus Exploitation in CMB B-Mode Experiments

A preferred method to detect the curl-component, or B-mode, signature of inflationary gravitational waves (IGWs) in the cosmic microwave background (CMB) polarization, in the absence of foregrounds and lensing, is a prolonged integration over a single patch of sky of a few square degrees. In practice, however, foregrounds abound and the sensitivity to B modes can be improved considerably by finding the region of sky cleanest of foregrounds. The best strategy to detect B modes thus involves a tradeoff between exploration (to find lower-foreground patches) and exploitation (through prolonged integration). This problem is akin to the multi-armed bandit (MAB) problem in probability theory, wherein a bandit faces a series of slot machines with unknown winning odds and must develop a strategy to maximize his/her winnings with some finite number of pulls. While the optimal MAB strategy remains to be determined, a number of algorithms have been developed in an effort to maximize the winnings. Here, we formulate the search for IGW B modes in the presence of spatially-varying foregrounds as an MAB problem and develop adaptive survey strategies to optimize the sensitivity to IGW B modes. We demonstrate, using realistic foreground models and taking lensing-induced B modes into account, that adaptive experiments can substantially improve the upper bound on the tensor-to-scalar ratio (by factors of 2-3 in single frequency experiments, and possibly even more). Similar techniques can be applied to other surveys, including 21-cm measurements of signatures of the epoch of reionization, searches for a stochastic primordial gravitational wave background, deep-field imaging by the James Webb Space Telescope or various radio interferometers, and transient follow-up searches.

Primordial black holes in non-Gaussian regimes [Replacement]

Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations. They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed. Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution – which depends on the amount of non-Gaussianity present. We first study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the power spectrum can vary by several orders of magnitude. The sign of the non-linearity parameters (f_{NL}, g_{NL}, etc) are particularly important. We also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete non-linear probability distribution is known, and find that truncating to any given order (i.e. to order f_{NL} or g_{NL}, etc) does not give accurate results.

Primordial black holes in non-Gaussian regimes

Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations. They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed. Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution – which depends on the amount of non-Gaussianity present. We first study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the power spectrum can vary by several orders of magnitude. The sign of the non-linearity parameters (f_{NL}, g_{NL}, etc) are particularly important. We also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete non-linear probability distribution is known, and find that truncating to any given order (i.e. to order f_{NL} or g_{NL}, etc) does not give accurate results.

The Effective Field Theory of Inflation Models with Sharp Features

We describe models of single-field inflation with small and sharp step features in the potential (and sound speed) of the inflaton field, in the context of the Effective Field Theory of Inflation. This approach allows us to study the effects of features in the power-spectrum and in the bispectrum of curvature perturbations, from a model-independent point of view, by parametrizing the features directly with modified "slow-roll" parameters. We can obtain a self-consistent power-spectrum, together with enhanced non-Gaussianity, which grows with a quantity $\beta$ that parametrizes the sharpness of the step. With this treatment it is straightforward to generalize and include features in other coefficients of the effective action of the inflaton field fluctuations. Our conclusion in this case is that, excluding extrinsic curvature terms, the only interesting effects at the level of the bispectrum could arise from features in the first slow-roll parameter $\epsilon$ or in the speed of sound $c_s$. Finally, we derive an upper bound on the parameter $\beta$ from the consistency of the perturbative expansion of the action for inflaton perturbations. This constraint can be used for an estimation of the signal-to-noise ratio, to show that the observable which is most sensitive to features is the power-spectrum. This conclusion would change if we consider the contemporary presence of a feature and a speed of sound $c_s < 1$, as, in such a case, contributions from an oscillating folded configuration can potentially make the bispectrum the leading observable for feature models.

The Parkes Pulsar Timing Array

The aims of the Parkes Pulsar Timing Array (PPTA) project are to 1) make a direct detection of gravitational waves, 2) improve the solar system planetary ephemeris and 3) develop a pulsar-based time scale. In this article we describe the project, explain how the data are collected and processed and describe current research. Our current data sets are able to place an upper bound on the gravitational wave background that is the most stringent to date.

Novel considerations about the error budget of the LAGEOS-based tests of frame-dragging with GRACE geopotential models [Cross-Listing]

A realistic assessment of the uncertainties in the even zonals of a given geopotential model must be made by directly comparing its coefficients with those of a wholly independent solution of superior formal accuracy. Otherwise, a favorable selective bias is introduced in the evaluation of the total error budget of the LAGEOS-based Lense-Thirring tests yielding likely too optimistic figures for it. By applying a novel approach which recently appeared in the literature, the second (L = 4) and the third (L = 6) even zonals turn out to be uncertain at a 2-3 10^-11 (L = 4) and 3-4 10^-11 (L = 6) level, respectively, yielding a total gravitational error of about 27-28%, with an upper bound of 37-39%. The results by Ries et al. themselves yield an upper bound for it of about 33%. The low-degree even zonals are not exclusively determined from the GRACE Satellite-to-Satellite Tracking (SST) range since they affect it with long-period, secular-like signatures over orbital arcs longer than one orbital period: GRACE SST is not accurately sensitive to such signals. Conversely, general relativity affects it with short-period effects as well. Thus, the issue of the a priori "imprinting" of general relativity itself in the GRACE-based models used so far remains open.

Reconciliation of High Energy Scale Models of Inflation with Planck [Cross-Listing]

The inflationary cosmology paradigm is very successful in explaining the CMB anisotropy to the percent level. Besides the dependence on the inflationary model, the power spectra, spectral tilt and non-Gaussianity of the CMB temperature fluctuations also depend on the initial state of inflation. Here, we examine to what extent these observables are affected by our ignorance in the initial condition for inflationary perturbations, due to unknown new physics at a high scale $M$. For initial states that satisfy constraints from backreaction, we find that the amplitude of the power spectra could still be significantly altered, while the modification in bispectrum remains small. For such initial states, $M$ has an upper bound of a few tens of $H$, with $H$ being the Hubble parameter during inflation. We show that for $M\sim 20 H$, such initial states always (substantially) suppress the tensor to scalar ratio. In particular we show that a general choice of initial conditions can satisfactorily reconcile the simple $\frac{1}{2}m^2 \phi^2$ chaotic model with the Planck data.

Reconciliation of High Energy Scale Models of Inflation with Planck [Replacement]

The inflationary cosmology paradigm is very successful in explaining the CMB anisotropy to the percent level. Besides the dependence on the inflationary model, the power spectra, spectral tilt and non-Gaussianity of the CMB temperature fluctuations also depend on the initial state of inflation. Here, we examine to what extent these observables are affected by our ignorance in the initial condition for inflationary perturbations, due to unknown new physics at a high scale $M$. For initial states that satisfy constraints from backreaction, we find that the amplitude of the power spectra could still be significantly altered, while the modification in bispectrum remains small. For such initial states, $M$ has an upper bound of a few tens of $H$, with $H$ being the Hubble parameter during inflation. We show that for $M\sim 20 H$, such initial states always (substantially) suppress the tensor to scalar ratio. In particular we show that a general choice of initial conditions can satisfactorily reconcile the simple ${1}{2}m^2 \phi^2$ chaotic model with the Planck data.

Chameleon Field Theories

Chameleons are light scalar fields with remarkable properties. Through the interplay of self-interactions and coupling to matter, chameleon particles have a mass that depends on the ambient matter density. The manifestation of the fifth force mediated by chameleons therefore depends sensitively on their environment, which makes for a rich phenomenology. In this article, we review two recent results on chameleon phenomenology. The first result a pair of no-go theorems limiting the cosmological impact of chameleons and their generalizations: i) the range of the chameleon force at cosmological density today can be at most ~Mpc; ii) the conformal factor relating Einstein- and Jordan-frame scale factors is essentially constant over the last Hubble time. These theorems imply that chameleons have negligible effect on the linear growth of structure, and cannot account for the observed cosmic acceleration except as some form of dark energy. The second result pertains to the quantum stability of chameleon theories. We show how requiring that quantum corrections be small, so as to allow reliable predictions of fifth forces, leads to an upper bound of m < 0.0073 (\rho/ 10 g cm^{-3})^{1/3} eV for gravitational strength coupling, whereas fifth force experiments place a lower bound of m>0.0042 eV. An improvement of less than a factor of two in the range of fifth force experiments could test all classical chameleon field theories whose quantum corrections are well-controlled and couple to matter with nearly gravitational strength regardless of the specific form of the chameleon potential.

Observations of ubiquitous compressive waves in the Sun's chromosphere

The details of the mechanism(s) responsible for the observed heating and dynamics of the solar atmosphere still remain a mystery. Magnetohydrodynamic (MHD) waves are thought to play a vital role in this process. Although it has been shown that incompressible waves are ubiquitous in off-limb solar atmospheric observations their energy cannot be readily dissipated. We provide here, for the first time, on-disk observation and identification of concurrent MHD wave modes, both compressible and incompressible, in the solar chromosphere. The observed ubiquity and estimated energy flux associated with the detected MHD waves suggest the chromosphere is a vast reservoir of wave energy with the potential to meet chromospheric and coronal heating requirements. We are also able to propose an upper bound on the flux of the observed wave energy that is able to reach the corona based on observational constraints, which has important implications for the suggested mechanism(s) for quiescent coronal heating.

Strong constraints on magnetized white dwarfs surpassing the Chandrasekhar mass limit

We show that recently proposed white dwarf models with masses well in excess of the Chandrasekhar limit, based on modifying the equation of state by a super-strong magnetic field in the centre, are very far from equilibrium because of the neglect of Lorentz forces. An upper bound on the central magnetic fields, from a spherically averaged hydrostatic equation, appears to be much smaller than the values assumed. Robust estimates of the Lorentz forces are also made without assuming spherical averaging. These again bear out the results obtained from a spherically averaged model. In our assessment, these rule out the possibility that magnetic tension could change the situation in favour of larger magnetic fields. We conclude that such super-Chandrasekhar models are unphysical and exploration of their astrophysical consequences is premature.

Brane Tension Constrictions Using Astrophysical Objects [Cross-Listing]

In this paper we investigate different astrophysical methods to obtain a brane tension bound. Using the modified Einstein equations in the brane with a vanishing non-local effects, we study the contributions of the modified radiated power by gravitational waves and propose an upper bound with this method. Also, using the stellar equilibrium theory, we study the Buchdahl’s theorem and the corrections caused by the branes, where it is assumed a constant density. Finally, with the Tolman-Oppenheimer-Volkoff equation and a perfect fluid equation of state, we study the relation between the density and the brane tension through a dynamical analysis.

Non-singular quantum-inspired gravitational collapse [Replacement]

We consider general relativistic homogeneous gravitational collapses for dust and radiation. We show that replacing the density profile with an effective density justified by some quantum gravity framework leads to the avoidance of the final singularity. The effective density acts on the collapsing cloud by introducing an isotropic pressure, which is negligible at the beginning of the collapse and becomes negative and dominant in the strong field regime. Event horizons never form and therefore the outcome of the collapse is not a black hole, in the sense that there are no regions causally disconnected from future null infinity. Apparent horizons form when the mass of the object exceeds a critical value, disappear when the matter density approaches an upper bound and gravity becomes very weak (asymptotic freedom regime), form again after the bounce as a consequence of the decrease in the matter density, and eventually disappear when the density becomes too low and the matter is radiated away. The possibility of detecting radiation coming from the high density region of a collapsing astrophysical object in which classically there would be the creation of a singularity could open a new window to experimentally test theories of quantum gravity.

Nonlinear Development of the R Mode Instability and the Maximum Rotation Rate of Neutron Stars [Replacement]

We describe how the nonlinear development of the R mode instability of neutron stars influences spin up to millisecond periods via accretion. Our arguments are based on nearly-resonant interactions of the R mode with pairs of "daughter modes". The amplitude of the R mode saturates at the lowest value for which parametric instability leads to significant excitation of a particular pair of daughters. The lower bound on this limiting amplitude is proportional to the damping rate of the daughter modes that are excited parametrically. Based on this picture, we show that if modes damp because of dissipation in a very thin boundary layer at the crust-core boundary then spin up to frequencies larger than about 300 Hz does not occur. Within this conventional scenario the R mode saturates at an amplitude that is too large for angular momentum gain from accretion to overcome gravitational loss to gravitational radiation. We conclude that lower dissipation is required for spin up to frequencies much higher than 300 Hz. We conjecture that if the transition from the fluid core to the crystalline crust occurs over a distance much longer than 1 cm then a sharp viscous boundary layer fails to form. In this case, damping is due to shear viscosity dissipation integrated over the entire star; the rate is slower than if a viscous boundary layer forms. We use statistical arguments and scaling relations to estimate the lowest parametric instability threshold from first principles. The resulting saturation amplitudes are low enough to permit spin up to higher frequencies. Further, we show that the requirement that the lowest parametric instability amplitude be small enough to allow continued spin up imposes an upper bound to the frequencies that may be attained via accretion that may plausibly be about 750 Hz. Within this framework, the R mode is unstable for all millisecond pulsars, whether accreting or not.

Nonlinear Development of the R Mode Instability and the Maximum Rotation Rate of Neutron Stars

We describe how the nonlinear development of the R mode instability of neutron stars influences spin up to millisecond periods via accretion. We begin by showing that the conventional picture in which modes damp because of dissipation in a very thin boundary layer at the crust-core boundary prevents spin up to frequencies larger than about 300 Hz, which is close to the spin frequency when the R mode first destabilizes. Within this conventional scenario the amplitude of the R mode, which saturates near its lowest parametric instability threshold because of interaction with other rotational modes, is large enough that angular momentum loss to gravitational radiation exceeds the angular momentum gain from accretion. We argue that if the transition from the fluid core to the crystalline crust occurs over a distance much longer than ~ 1 cm then a sharp viscous boundary layer fails to form. In that case, modes dissipate primarily via ordinary shear viscosity distributed over the bulk of the star. The slower damping rates that result allow a smaller lowest parametric instability amplitude for the R mode, and therefore permit spin up to higher frequencies. Further, we show that the requirement that the lowest parametric instability amplitude be small enough to allow continued spin up imposes an upper bound to the frequencies that may be attained via accretion that may plausibly be about 750 Hz. Within this framework, the R mode is unstable for all millisecond pulsars, whether accreting or not.

AMS02 results support the secondary origin of cosmic ray positrons

We show that the recent AMS02 positron fraction measurement is consistent with a secondary origin for positrons, and does not require additional primary sources such as pulsars or dark matter. The measured positron fraction at high energy saturates the previously predicted upper bound for secondary production (Katz et al 2009), obtained by neglecting radiative losses. This coincidence, which will be further tested by upcoming AMS02 data at higher energy, is a compelling indication for a secondary source. Within the secondary model the AMS02 data imply a cosmic ray propagation time in the Galaxy of < Myr and an average traversed interstellar matter density of order 1/cc, comparable to the density of the Milky Way gaseous disk, at a rigidity of 300 GV.

First observational constraints on tensor non-Gaussianity sourced by primordial magnetic fields from cosmic microwave background

Primordial magnetic fields (PMFs) create a large squeezed-type non-Gaussianity in tensor perturbation, which generates non-Gaussian temperature fluctuations in the cosmic microwave background (CMB). We for the first time derive an observational constraint on such tensor non-Gaussianity from observed CMB maps. Analyzing temperature maps of the WMAP 7-year data, we find such tensor non-Gaussianity is consistent with zero. This gives an upper bound on PMF strength smoothed on $1 ~ {\rm Mpc}$ as $B_{1 ~ \rm Mpc} < 3.2 {\rm nG}$ at 95% CL. We discuss some difficulties in constraining tensor non-Gaussianity due to spin and angle dependence of resultant CMB bispectrum.

Determination of z~0.8 neutral hydrogen fluctuations using the 21 cm intensity mapping auto-correlation

The large-scale distribution of neutral hydrogen in the universe will be luminous through its 21 cm emission. Here, for the first time, we use the auto-power spectrum of 21 cm intensity fluctuations to constrain neutral hydrogen fluctuations at z~0.8. Our data were acquired with the Green Bank Telescope and span the redshift range 0.6 < z < 1 over two fields totaling ~41 deg. sq. and 190 hr of radio integration time. The dominant synchrotron foregrounds exceed the signal by ~10^3, but have fewer degrees of freedom and can be removed efficiently. Even in the presence of residual foregrounds, the auto-power can still be interpreted as an upper bound on the 21 cm signal. Our previous measurements of the cross-correlation of 21 cm intensity and the WiggleZ galaxy survey provide a lower bound. Through a Bayesian treatment of signal and foregrounds, we can combine both fields in auto- and cross-power into a measurement of Omega_HI b_HI = [0.62^{+0.23}_{-0.15}] * 10^{-3} at 68% confidence with 9% systematic calibration uncertainty, where Omega_HI is the neutral hydrogen (HI) fraction and b_HI is the HI bias parameter. We describe observational challenges with the present dataset and plans to overcome them.

Determination of z~0.8 neutral hydrogen fluctuations using the 21 cm intensity mapping auto-correlation [Replacement]

The large-scale distribution of neutral hydrogen in the Universe will be luminous through its 21 cm emission. Here, for the first time, we use the auto-power spectrum of 21 cm intensity fluctuations to constrain neutral hydrogen fluctuations at z~0.8. Our data were acquired with the Green Bank Telescope and span the redshift range 0.6 < z < 1 over two fields totalling ~41 deg. sq. and 190 h of radio integration time. The dominant synchrotron foregrounds exceed the signal by ~10^3, but have fewer degrees of freedom and can be removed efficiently. Even in the presence of residual foregrounds, the auto-power can still be interpreted as an upper bound on the 21 cm signal. Our previous measurements of the cross-correlation of 21 cm intensity and the WiggleZ galaxy survey provide a lower bound. Through a Bayesian treatment of signal and foregrounds, we can combine both fields in auto- and cross-power into a measurement of Omega_HI b_HI = [0.62^{+0.23}_{-0.15}] * 10^{-3} at 68% confidence with 9% systematic calibration uncertainty, where Omega_HI is the neutral hydrogen (HI) fraction and b_HI is the HI bias parameter. We describe observational challenges with the present data set and plans to overcome them.

How stable is the photon? [Replacement]

Yes, the photon. While a nonzero photon mass has been under experimental and theoretical study for years, the possible implication of a finite photon lifetime lacks discussion. The tight experimental upper bound of the photon mass restricts the kinematically allowed final states of photon decay to the lightest neutrino and/or particles beyond the Standard Model. We discuss the modifications of the well-measured cosmic microwave background spectrum of free streaming photons due to photon mass and lifetime and obtain model-independent constraints on both parameters—most importantly a lower direct bound of 3 yr on the photon lifetime, should the photon mass be at its conservative upper limit. In that case, the lifetime of microwave photons will be time-dilated by a factor order 10^(15).

How stable is the photon? [Cross-Listing]

Yes, the photon. While a nonzero photon mass has been under experimental and theoretical study for years, the possible implication of a finite photon lifetime lacks discussion. The tight experimental upper bound of the photon mass restricts the kinematically allowed final states of photon decay to the lightest neutrino and/or particles beyond the Standard Model. We discuss the modifications of the well-measured cosmic microwave background spectrum of free streaming photons due to photon mass and lifetime and obtain model-independent constraints on both parameters—most importantly a lower direct bound of 3 yrs on the photon lifetime, should the photon mass be at its conservative upper limit.

Planck 2013 results. XXII. Constraints on inflation

We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to n_s = 0.960 pm 0.0073, ruling out exact scale invariance at over 5 sigma. Planck establishes an upper bound on the tensor-to-scalar ratio at r < 0.11 (95% CL). Planck data shrink the space of allowed standard inflationary models, preferring potentials with V” < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n > 2 do not provide a good fit to the data. Planck does not find any statistically significant running of the scalar spectral index, obtaining d n_s/d ln k = -0.0134 pm 0.0090. Several analyses dropping the slow-roll approximation are carried out, including detailed model comparison and inflationary potential reconstruction. We investigate whether the primordial power spectrum contains any features. A penalized likelihood approach suggests a feature near the smallest scales probed by Planck at an estimated significance of ~3 sigma after correction for the look elsewhere effect. Models with a parameterized oscillatory feature can improve the fit chi^2 by ~ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with bounds on f_NL measured by Planck. The fractional primordial contribution of CDM isocurvature modes in the curvaton and axion scenarios has upper bounds of 0.25% or 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelation can improve chi^2 by ~4 due to a moderate tension between l < 40 and higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions.

A Consistency Relation for Single-Field Inflation with Power Spectrum Oscillations [Cross-Listing]

We derive a theoretical upper bound on the oscillation frequency in the scalar perturbation power spectrum of single-field inflation. Oscillations are most naturally produced by modified vacua with varying phase. When this phase changes rapidly, it induces strong interactions between the scalar fluctuations. If the interactions are sufficiently strong the theory cannot be evaluated using perturbation theory, hence imposing a limit on the oscillation frequency. This complements the bound found by Weinberg governing the validity of effective field theory. The generalized consistency relation also allows one to use squeezed configurations of higher-point correlations to place constraints on the power spectrum oscillations.

Invisible decays of ultra-high energy neutrinos [Cross-Listing]

Gamma-ray bursts (GRBs) are expected to provide a source of ultra high energy cosmic rays, accompanied with potentially detectable neutrinos at neutrino telescopes. Recently, IceCube has set an upper bound on this neutrino flux well below theoretical expectation. We investigate whether this mismatch between expectation and observation can be due to neutrino decay. We demosntrate the phenomenological consistency and and theoretical plausibility of the neutrino decay hypothesis. A potential implication is the observability of majoron-emitting neutrinoless double beta decay.

Luminosity Evolution of Rotation-powered Gamma-ray Pulsars

We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resultant gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial ten thousand years, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater but increases less rapidly than what a light element envelope has. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis.

Constraints on Neutrino Mass from Sunyaev--Zeldovich Cluster Surveys [Replacement]

The presence of massive neutrinos has a characteristic impact on the growth of large scale structures such as galaxy clusters. We forecast on the capability of the number count and power spectrum measured from the ongoing and future Sunyaev-Zeldovich (SZ) cluster surveys, combined with cosmic microwave background (CMB) observation to constrain the total neutrino mass $\mnu$ in a flat $\Lambda$CDM cosmology. We adopt self-calibration for the mass-observable scaling relation, and evaluate constraints for the South Pole Telescope normal and with polarization (SPT, SPTPol), Planck, and Atacama Cosmology Telescope Polarization (ACTPol) surveys. We find that a sample of $\approx1000$ clusters obtained from the Planck cluster survey plus extra information from CMB lensing extraction could tighten the current upper bound on the sum of neutrino masses to $\sigma_{\mnu}=0.17$ eV at 68% C.L. Our analysis shows that cluster number counts and power spectrum provide complementary constraints and as a result they help reducing the error bars on $\mnu$ by a factor of 4-8 when both probes are combined. We also show that the main strength of cluster measurements in constraining $\mnu$ is when good control of cluster systematics is available. When applying a weak prior on the mass-observable relations, which can be at reach in the upcoming cluster surveys, we obtain $\sigma_{\mnu}=0.48$ eV using cluster only probes and, more interestingly, $\sigma_{\mnu}=0.08$ eV using cluster + CMB which corresponds to a $S/N\approx4$ detection for $\mnu\ge0.3$ eV. We analyze and discuss the degeneracies of $\mnu$ with other parameters and investigate the sensitivity of neutrino mass constraints with various surveys specifications.

Constraints on Neutrino Mass from Sunyaev--Zeldovich Cluster Surveys

The presence of massive neutrinos has a characteristic impact on the growth of large scale structures such as galaxy clusters. We forecast on the capability of the number count and power spectrum measured from the ongoing and future Sunyaev-Zeldovich (SZ) cluster surveys, combined with cosmic microwave background (CMB) observation to constrain the total neutrino mass $\mnu$ in a flat $\Lambda$CDM cosmology. We adopt self-calibration for the mass-observable scaling relation, and evaluate constraints for the South Pole Telescope normal and with polarization (SPT, SPTPol), Planck, and Atacama Cosmology Telescope Polarization (ACTPol) surveys. We find that a sample of $\approx1000$ clusters obtained from the Planck cluster survey plus extra information from CMB lensing extraction could tighten the current upper bound on the sum of neutrino masses to $\sigma_{\mnu}=0.17$ eV at 68% C.L. Our analysis shows that cluster number counts and power spectrum provide complementary constraints and as a result they help reducing the error bars on $\mnu$ by a factor of 4-8 when both probes are combined. We also show that the main strength of cluster measurements in constraining $\mnu$ is when good control of cluster systematics is available. When applying a weak prior on the mass-observable relations, which can be at reach in the upcoming cluster surveys, we obtain $\sigma_{\mnu}=0.48$ eV using cluster only probes and, more interestingly, $\sigma_{\mnu}=0.08$ eV using cluster + CMB which corresponds to a $S/N\approx4$ detection for $\mnu\ge0.3$ eV. We analyze and discuss the degeneracies of $\mnu$ with other parameters and investigate the sensitivity of neutrino mass constraints with various surveys specifications.

Dependence of the optical brightness on the gamma and X-ray properties of GRBs

The Swift satellite made a real break through with measuring simultaneously the gamma X-ray and optical data of GRBs, effectively. Although, the satellite measures the gamma, X-ray and optical properties almost in the same time a significant fractions of GRBs remain undetected in the optical domain. In a large number of cases only an upper bound is obtained. Survival analysis is a tool for studying samples where a part of the cases has only an upper (lower) limit. The obtained survival function may depend on some other variables. The Cox regression is a way to study these dependencies. We studied the dependence of the optical brightness (obtained by the UVOT) on the gamma and X-ray properties, measured by the BAT and XRT on board of the Swift satellite. We showed that the gamma peak flux has the greatest impact on the afterglow’s optical brightness while the gamma photon index and the X-ray flux do not. This effect probably originates in the energetics of the jet launched from the central engine of the GRB which triggers the afterglow.

Can one observe quantum-gravitational effects in the cosmic microwave background? [Cross-Listing]

In order to find the correct theory of quantum gravity, one has to look for observational effects in any candidate theory. Here, we focus on canonical quantum gravity and calculate the quantum-gravitational contributions to the anisotropy spectrum of the cosmic microwave background that arise from a semiclassical approximation to the Wheeler-DeWitt equation. While the resulting modification of the power spectrum at large scales is too weak to be observable, we find an upper bound on the energy scale of inflation.

 

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