1,354,978 research outputs found
Discrete symmetries and localization in a brane-world
No full textDiscrete symmetries are studied in warped space-times with one extra dimension. In particular, we analyze the compatibility of five- and four-dimensional charge conjugation, parity, time reversal, and the orbifold symmetry Z2 with localization of fermions on the four-dimensional brane-world and Lorentz invariance. We then show that, when a suitable topological scalar field (the "kink") is included, fermion localization is a consequence of (five-dimensional) CPT invariance. ©2001 The American Physical Society
On boundary terms and conformal transformations in curved spacetimes
No full textWe intend to clarify the interplay between boundary terms and conformal transformations in scalar-tensor theories of gravity. We first consider the action for pure gravity in five dimensions and show that, on compactifing a la Kaluza-Klein to four dimensions, one obtains the correct boundary terms in the Jordan (or String) Frame form of the Brans-Dicke action. Further, we analyze how the boundary terms change under the conformal transformations which lead to the Pauli (or Einstein) frame and to the nonminimally coupled massless scalar field. In particular, we study the behaviour of the total energy in asymptotically flat spacetimes as it results from surface terms in the Hamiltonian formalism
Observational Hints of a Pre--Inflationary Scale?
No full textWe argue that the lack of power exhibited by cosmic microwave background (CMB) anisotropies at large angular scales might be linked to the onset of inflation. We highlight observational features and theoretical hints that support this view, and present a preliminary estimate of the physical scale that would underlie the phenomenon.We argue that the lack of power exhibited by cosmic microwave background (CMB) anisotropies at large angular scales might be linked to the onset of inflation. We highlight observational features and theoretical hints that support this view, and present a preliminary estimate of the physical scale that would underlie the phenomenon
Light Bending as a Probe of the Nature of Dark Energy
No full textWe study the bending of light for static spherically symmetric (SSS) space-times which include a dark energy contribution. Geometric dark energy models generically predict a correction to the Einstein angle written in terms of the distance to the closest approach, whereas a cosmological constant does not.
While dark energy is associated with a repulsive force in cosmological context, its effect on null geodesics in SSS space-times can be attractive as for the Newtonian term. This dark energy contribution may not be negligible with respect to the Einstein prediction in lensing involving clusters of galaxies. Strong lensing may therefore be useful to distinguish from other dark energy models
CMB acoustic scale in the entropic-like accelerating universe
No full textWe consider generalizations of the entropic accelerating universe recently proposed in [D. A. Easson, P. H. Frampton, and G. F. Smoot, Phys. Lett. B 696, 273 (2011).] and [D. A. Easson, P. H. Frampton, and G. F. Smoot, arXiv:1003.1528.] and show that their background equations can be made equivalent to a model with a dark energy component with a constant parameter of state wX=-1+2γ/3, where γ is related to the coefficients of the new terms in the Friedmann equations. After discussing all the Friedmann equations for an arbitrary γ, we show how to recover the standard scalings for dust and radiation. The acoustic scale ℓA, related to the peak positions in the pattern of the angular power spectrum of the cosmic microwave background anisotropies, is also computed and yields the stringent bound |γ|≪1. We then argue that future data might be able to distinguish this model from pure ΛCDM (corresponding to γ=0)
Electromagnetic contributions to lepton g - 2 In a thick brane-world
No full textWe consider Standard Model fields living inside a thick four-dimensional flat brane embedded in a (possibly warped) five-dimensional space-time and estimate the electromagnetic corrections to the anomalous magnetic moment (g - 2) of the electron and muon by including virtual massive fermion and gauge boson states. Constraints on the mass of the 'excited' states (or thickness of the brane-world) are obtained. (C) 2000 Elsevier Science B.V
Nonminimally coupled scalar fields in homogeneous universes
No full textThe equations governing the evolution of non-minimally coupled scalar matter and the scale factor of a Robertson-Walker universe are derived from a minisuperspace action. As for the minimally coupled case, it is shown that the entire semiclassical dynamics can be retrieved from the Wheeler-DeWitt equation via the Born-Oppenheimer reduction, which properly yields the (time-time component of the) covariantly conserved energy-momentum tensor of the scalar field as the source term for gravity. However, for a generic coupling, the expectation value of the operator which evolves the matter state in time is not equal to the source term in the semiclassical Einstein equation for the scale factor of the universe and the difference between these two quantities is related to the squeezing and quantum fluctuations of the matter state. We also argue that matter quantum fluctuations become relevant in an intermediate regime between quantum gravity and semiclassical gravity and study several cases in detail. © 2000 The American Physical Society
Testing discrete symmetries with the cosmic microwave background: current constraints and Planck forecasts
No full textAnisotropy and polarization of the CMB are probing cosmological models with unprecedented precision. The WMAP satellite data are largely consistent with concordance ACDM cosmology. However, intriguing flukes are known to exist that may pinpoint at physics beyond the standard model. Constraining the violations of discrete symmetries in the CMB pattern is a promising mean to investigate these discrepancies. In this paper we constrain the Parity and CPT symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon. Finally, we provide forecasts for Planck and we discuss how emission from a specific diffuse foreground component arising within the Solar System needs to be kept under strict control to avoid incurring into false positive detections
Pre-Inflationary Relics in the CMB?
No full textString Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending CDM with a scale related to the infrared depression and explore the constraints allowed by {\sc Planck} data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with , we thus find \Delta = (0.351 \pm 0.114) \times 10^{-3} \, \mbox{Mpc}^{-1}, at confidence level, to be compared with a nearby value at with the standard mask. With about 64 --folds of inflation, these values for would translate into primordial energy scales GeV.String Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending CDM with a scale related to the infrared depression and explore the constraints allowed by {\sc Planck} data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with , we thus find \Delta = (0.351 \pm 0.114) \times 10^{-3} \, \mbox{Mpc}^{-1}, at confidence level, to be compared with a nearby value at with the standard mask. With about 64 --folds of inflation, these values for would translate into primordial energy scales GeV.String Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending ΛCDM with a scale Δ related to the infrared depression and explore the constraints allowed by Planck 2015 data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with fsky=39% , we thus find Δ=(0.351±0.114)×10−3Mpc−1 , at 99.4% confidence level, to be compared with a nearby value at 88.5% with the standard fsky=94% mask. With about 64 e -folds of inflation, these values for Δ would translate into primordial energy scales O(1014)GeV
The Planck mission: From first results to cosmology
No full textPlanck is a ESA satellite, currently in operation, whose main objective is to accurately image the anisotropies of the Cosmic Microwave Background Radiation in intensity and polarization. Benefiting from an unprecedented combination
of sensitivity, angular resolution, and frequency leverage, Planck will provide high quality data to be mined in cosmology and astrophysics. The first Planck results have been released in January 2011 and include both Galactic and extragalactic source catalogues, a list of galaxy clusters selected by the Sunyaev-Zel’dovich effect, and a cold cores catalogue. The first cosmological data products are awaited for early 2013. Planck has a wide list of scientific targets. Here we focus on one specific aspect which is also of interest to the high energy physics community: constraining the Parity and CPT symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide
marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon
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