Showing papers in "Physical Review D in 2002"
TL;DR: In this paper, a fast Markov chain Monte Carlo exploration of cosmological parameter space is presented, which combines data from the CMB, HST Key Project, 2dF galaxy redshift survey, supernovae type Ia and big-bang nucleosynthesis.
Abstract: We present a fast Markov chain Monte Carlo exploration of cosmological parameter space. We perform a joint analysis of results from recent cosmic microwave background ~CMB! experiments and provide parameter constraints, including s 8, from the CMB independent of other data. We next combine data from the CMB, HST Key Project, 2dF galaxy redshift survey, supernovae type Ia and big-bang nucleosynthesis. The Monte Carlo method allows the rapid investigation of a large number of parameters, and we present results from 6 and 9 parameter analyses of flat models, and an 11 parameter analysis of non-flat models. Our results include constraints on the neutrino mass ( mn&0.3 eV), equation of state of the dark energy, and the tensor amplitude, as well as demonstrating the effect of additional parameters on the base parameter constraints. In a series of appendixes we describe the many uses of importance sampling, including computing results from new data and accuracy correction of results generated from an approximate method. We also discuss the different ways of converting parameter samples to parameter constraints, the effect of the prior, assess the goodness of fit and consistency, and describe the use of analytic marginalization over normalization parameters.
3,550 citations
TL;DR: In this article, the authors show that the hierarchy of scales can be fixed by a choice of Ramond-Ramond and Neveu-Schwarz fluxes in the compact manifold, and give examples involving orientifold compactifications of type IIB string theory and F-theory compactifications on Calabi-Yau fourfolds.
Abstract: Warped compactifications with significant warping provide one of the few known mechanisms for naturally generating large hierarchies of physical scales. We demonstrate that this mechanism is realizable in string theory, and give examples involving orientifold compactifications of type-IIB string theory and F-theory compactifications on Calabi-Yau fourfolds. In each case, the hierarchy of scales is fixed by a choice of Ramond-Ramond and Neveu-Schwarz fluxes in the compact manifold. Our solutions involve compactifications of the Klebanov-Strassler gravity dual to a confining $\mathcal{N}=1$ supersymmetric gauge theory, and the hierarchy reflects the small scale of chiral symmetry breaking in the dual gauge theory.
2,548 citations
Journal Article•
2,092 citations
TL;DR: In this paper, the authors consider the evolution of a universe evolving from a phase dominated by nonrelativistic matter to a cosmological constant via an intermediate period where the effective equation of state is given by $p=\ensuremath{\alpha{-}A/{\ensemath{\rho}}^{\ensemblem{\alpha}},$ where A is a positive constant and $0l √ √ 1/ √ l 1/1.
Abstract: We consider the scenario emerging from the dynamics of a generalized Born-Infeld theory. The equation of state describing this system is given in terms of the energy density $\ensuremath{\rho}$ and pressure p by the relationship $p=\ensuremath{-}A/{\ensuremath{\rho}}^{\ensuremath{\alpha}},$ where A is a positive constant and $0l\ensuremath{\alpha}l~1.$ We discuss the conditions under which homogeneity arises and show that this equation of state describes the evolution of a universe evolving from a phase dominated by nonrelativistic matter to a phase dominated by a cosmological constant via an intermediate period where the effective equation of state is given by $p=\ensuremath{\alpha}\ensuremath{\rho}.$
1,885 citations
TL;DR: In this article, the leading-order Lagrangian is derived using power counting and gauge invariance in the effective theory, and the factorization of soft and ultrasoft gluons from collinear particles is shown at the level of operators in effective field theory.
Abstract: The factorization of soft and ultrasoft gluons from collinear particles is shown at the level of operators in an effective field theory. Exclusive hadronic factorization and inclusive partonic factorization follow as special cases. The leading-order Lagrangian is derived using power counting and gauge invariance in the effective theory. Several species of gluons are required, and softer gluons appear as background fields to gluons with harder momenta. Two examples are given: the factorization of soft gluons in $\stackrel{\ensuremath{\rightarrow}}{B}D\ensuremath{\pi}$ and the soft-collinear convolution for the $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}$ spectrum.
1,319 citations
TL;DR: In this article, the accelerated universe could be the result of gravitational leakage into extra dimensions over Hubble distances rather than the consequence of a nonzero cosmological constant, rather than a non-zero constant.
Abstract: We discuss the idea that the accelerated universe could be the result of gravitational leakage into extra dimensions over Hubble distances rather than the consequence of a nonzero cosmological constant.
1,097 citations
TL;DR: In this paper, a scalar field with a potential to reproduce the observed evolution of the universe cannot be reconciled with theoretical prejudices, and a recipe for determining the potential from a given expansion factor is given.
Abstract: It is an accepted practice in cosmology to invoke a scalar field with a potential $V(\ensuremath{\varphi})$ when the observed evolution of the universe cannot be reconciled with theoretical prejudices. Since one function degree of freedom in the expansion factor $a(t)$ can be traded off for the function $V(\ensuremath{\varphi}),$ it is always possible to find a scalar field potential which will reproduce a given evolution. I provide a recipe for determining $V(\ensuremath{\varphi})$ from $a(t)$ in two cases: (i) a normal scalar field with the Lagrangian $\mathcal{L}=(1/2){\ensuremath{\partial}}_{a}\ensuremath{\varphi}{\ensuremath{\partial}}^{a}\ensuremath{\varphi}\ensuremath{-}V(\ensuremath{\varphi})$ used in quintessence or dark energy models; (ii) a tachyonic field with the Lagrangian $\mathcal{L}=\ensuremath{-}V(\ensuremath{\varphi})[1\ensuremath{-}{\ensuremath{\partial}}_{a}\ensuremath{\varphi}\ensuremath{\partial}{}^{a}\ensuremath{\varphi}{]}^{1/2},$ motivated by recent string theoretic results. In the latter case, it is possible to have accelerated expansion of the universe during the late phase in certain cases.
1,010 citations
TL;DR: In the case of the CERN Large Hadron Collider, the high energy black hole cross section grows with energy at a rate determined by the dimensionality and geometry of the extra dimensions as discussed by the authors.
Abstract: If the fundamental Planck scale is of order of a TeV, as is the case in some extra-dimension scenarios, future hadron colliders such as the CERN Large Hadron Collider will be black hole factories. The nonperturbative process of black hole formation and decay by Hawking evaporation gives rise to spectacular events with up to many dozens of relatively hard jets and leptons with a characteristic ratio of hadronic to leptonic activity of roughly 5:1. The total transverse energy of such events is typically a sizable fraction of the beam energy. Perturbative hard scattering processes at energies well above the Planck scale are cloaked behind a horizon, thus limiting the ability to probe short distances. The high energy black hole cross section grows with energy at a rate determined by the dimensionality and geometry of the extra dimensions. This dependence therefore probes the extra dimensions at distances larger than the Planck scale.
966 citations
TL;DR: In this article, a cyclic model of the universe is proposed based on concepts drawn from the ekpyrotic scenario and M theory, and the universe undergoes an endless sequence of cosmic epochs.
Abstract: Based on concepts drawn from the ekpyrotic scenario and M theory, we elaborate our recent proposal of a cyclic model of the universe. In this model, the universe undergoes an endless sequence of cosmic epochs which begin with the universe expanding from a ``big bang'' and end with the universe contracting to a ``big crunch.'' Matching from ``big crunch'' to ``big bang'' is performed according to the prescription recently proposed with Khoury, Ovrut and Seiberg. The expansion part of the cycle includes a period of radiation and matter domination followed by an extended period of cosmic acceleration at low energies. The cosmic acceleration is crucial in establishing the flat and vacuous initial conditions required for ekpyrosis and for removing the entropy, black holes, and other debris produced in the preceding cycle. By restoring the universe to the same vacuum state before each big crunch, the acceleration ensures that the cycle can repeat and that the cyclic solution is an attractor.
783 citations
TL;DR: In this paper, conditions under which a universe contracting towards a big crunch can make a transition to an expanding big bang universe are considered, and the possibility opens the door to new classes of cosmological models.
Abstract: We consider conditions under which a universe contracting towards a big crunch can make a transition to an expanding big bang universe. A promising example is 11-dimensional M theory in which the eleventh dimension collapses, bounces, and reexpands. At the bounce, the model can reduce to a weakly coupled heterotic string theory and, we conjecture, it may be possible to follow the transition from contraction to expansion. The possibility opens the door to new classes of cosmological models. For example, we discuss how it suggests a major simplification and modification of the recently proposed ekpyrotic scenario.
701 citations
TL;DR: In this article, the solution of type IIB superstring theory in the maximally supersymmetric plane-wave background with constant null Ramond-Ramond 5-form field strength was described.
Abstract: We describe in detail the solution of type IIB superstring theory in the maximally supersymmetric plane-wave background with constant null Ramond-Ramond 5-form field strength. The corresponding light-cone Green-Schwarz action found by Metsaev is quadratic in both bosonic and fermionic coordinates. We obtain the light-cone Hamiltonian and the string representation of the corresponding supersymmetry algebra. The superstring Hamiltonian has a ``harmonic-oscillator'' form in both the string oscillator and the zero-mode parts and thus has a discrete spectrum. We analyze the structure of the zero-mode sector of the theory, establishing the precise correspondence between the lowest-lying ``massless'' string states and the type IIB supergravity fluctuation modes in the plane-wave background. The zero-mode spectrum has a certain similarity to the supergravity spectrum in ${\mathrm{AdS}}_{5}\ifmmode\times\else\texttimes\fi{}{\mathrm{S}}^{5}$ background of which the plane-wave background is a special limit. We also compare the plane-wave string spectrum with the expected form of the light-cone gauge spectrum of the ${\mathrm{AdS}}_{5}\ifmmode\times\else\texttimes\fi{}{\mathrm{S}}^{5}$ superstring.
TL;DR: In this article, a detailed investigation of effects both external to and internal to the spacecraft, as well as those due to modeling and computational techniques, is provided, including the methods, theoretical models, and experimental techniques used to detect and study small forces acting on interplanetary spacecraft.
Abstract: Our previous analyses of radio Doppler and ranging data from distant spacecraft in the solar system indicated that an apparent anomalous acceleration is acting on Pioneer 10 and 11, with a magnitude ${a}_{P}\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8} {\mathrm{c}\mathrm{m}/\mathrm{s}}^{2},$ directed towards the Sun. Much effort has been expended looking for possible systematic origins of the residuals, but none has been found. A detailed investigation of effects both external to and internal to the spacecraft, as well as those due to modeling and computational techniques, is provided. We also discuss the methods, theoretical models, and experimental techniques used to detect and study small forces acting on interplanetary spacecraft. These include the methods of radio Doppler data collection, data editing, and data reduction. There is now further data for the Pioneer 10 orbit determination. The extended Pioneer 10 data set spans 3 January 1987 to 22 July 1998. (For Pioneer 11 the shorter span goes from 5 January 1987 to the time of loss of coherent data on 1 October 1990.) With these data sets and more detailed studies of all the systematics, we now give a result of ${a}_{P}=(8.74\ifmmode\pm\else\textpm\fi{}1.33)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ ${\mathrm{c}\mathrm{m}/\mathrm{s}}^{2}.$ (Annual-diurnal variations on top of ${a}_{P},$ that leave ${a}_{P}$ unchanged, are also reported and discussed.)
TL;DR: In this article, the soft-collinear effective theory is used to simplify proofs of factorization formulas in highly energetic hadronic processes, and the formalism is applicable to both exclusive and inclusive factorization.
Abstract: In this paper we show how gauge symmetries in an effective theory can be used to simplify proofs of factorization formulas in highly energetic hadronic processes. We use the soft-collinear effective theory, generalized to deal with back-to-back jets of collinear particles. Our proofs do not depend on the choice of a particular gauge, and the formalism is applicable to both exclusive and inclusive factorization. As examples we treat the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\gamma}$ form factor $(\ensuremath{\gamma}{\ensuremath{\gamma}}^{*}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}),$ light meson form factors $({\ensuremath{\gamma}}^{*}\stackrel{\ensuremath{\rightarrow}}{M}M),$ as well as deep inelastic scattering ${(e}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{p}{e}^{\ensuremath{-}}X),$ the Drell-Yan process $(p\overline{p}\ensuremath{\rightarrow}{\mathrm{Xl}}^{+}{l}^{\ensuremath{-}}),$ and deeply virtual Compton scattering $({\ensuremath{\gamma}}^{*}\stackrel{\ensuremath{\rightarrow}}{p}{\ensuremath{\gamma}}^{(*)}p).$
TL;DR: In this article, the authors performed an investigation of the Lorentz-violating electrodynamics extracted from the renormalizable sector of the general CPT-and CPT violating standard model extension.
Abstract: An investigation is performed of the Lorentz-violating electrodynamics extracted from the renormalizable sector of the general Lorentz- and CPT-violating standard-model extension. Among the unconventional properties of radiation arising from Lorentz violation is birefringence of the vacuum. Limits on the dispersion of light produced by galactic and extragalactic objects provide bounds of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ on certain coefficients for Lorentz violation in the photon sector. The comparative spectral polarimetry of light from cosmologically distant sources yields stringent constraints of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}32}.$ All remaining coefficients in the photon sector are measurable in high-sensitivity tests involving cavity-stabilized oscillators. Experimental configurations in Earth- and space-based laboratories are considered that involve optical or microwave cavities and that could be implemented using existing technology.
TL;DR: In this article, the authors model massive dark objects in galactic nuclei as spherically symmetric static naked singularities in the Einstein massless scalar field theory and study the resulting gravitational lensing in detail.
Abstract: We model massive dark objects in galactic nuclei as spherically symmetric static naked singularities in the Einstein massless scalar field theory and study the resulting gravitational lensing in detail. Based on whether or not a naked singularity is covered within a photon sphere we classify naked singularities into two kinds: weakly naked (those contained within at least one photon sphere) and strongly naked (those not contained within any photon sphere). The qualitative features of gravitational lensing due to a weakly naked singularity are similar to those due to a Schwarzschild black hole (these give rise to one Einstein ring but no radial critical curve). However, the gravitational lensing due to a strongly naked singularity is qualitatively different from that due to a Schwarzschild black hole; a strongly naked singularity gives rise to either two or nil Einstein ring(s) and one radial critical curve. A light ray passing close to a photon sphere of a black hole or a weakly naked singularity goes around its photon sphere once, twice, or many times (before reaching an observer) depending upon the impact parameter and thus gives rise to a sequence of theoretically infinite number of relativistic images, which are highly demagnified. A strongly naked singularity produces no relativistic images.
TL;DR: In this paper, it was shown that the near-horizon description of a D5-D3 brane configuration in string theory, realized as AdS_5 x S^5 bisected by an AdS-4 x S 2 "brane", is dual to N=4 Super Yang-Mills theory in R^4 coupled to an R^3 defect.
Abstract: We develop both the gravity and field theory sides of the Karch-Randall conjecture that the near-horizon description of a certain D5-D3 brane configuration in string theory, realized as AdS_5 x S^5 bisected by an AdS_4 x S^2 "brane", is dual to N=4 Super Yang-Mills theory in R^4 coupled to an R^3 defect. We propose a complete Lagrangian for the field theory dual, a novel "defect superconformal field theory" wherein a subset of the fields of N=4 SYM interacts with a d=3 SU(N) fundamental hypermultiplet on the defect preserving conformal invariance and 8 supercharges. The Kaluza-Klein reduction of wrapped D5 modes on AdS_4 x S^2 leads to towers of short representations of OSp(4|4), and we construct the map to a set of dual gauge-invariant defect operators O_3 possessing integer conformal dimensions. Gravity calculations of and are given. Spacetime and N-dependence matches expectations from dCFT, while the behavior as functions of λ = g^2 N at strong and weak coupling is generically different. We comment on a class of correlators for which a non-renormalization theorem may still exist. Partial evidence for the conformality of the quantum theory is given, including a complete argument for the special case of a U(1) gauge group. Some weak coupling arguments which illuminate the duality are presented.
TL;DR: In this article, it was shown that the exact solutions of the model are continuous in the mass, yet the perturbative expansion exhibits a discontinuity in the leading order and singularities in higher orders as in the four-dimensional case.
Abstract: We address the question of whether a graviton could have a small nonzero mass. The issue is subtle for two reasons: there is a discontinuity in the mass in the lowest tree-level approximation, and, moreover, the nonlinear four-dimensional theory of a massive graviton is not defined unambiguously. First, we reiterate the old argument that for vanishing graviton mass the lowest tree-level approximation breaks down since the higher order corrections are singular in the graviton mass. However, there can exist nonperturbative solutions which correspond to the summation of the singular terms, and these solutions are continuous in the graviton mass. Furthermore, we study a completely nonlinear and generally covariant five-dimensional model which mimics the properties of the four-dimensional theory of massive gravity. We show that the exact solutions of the model are continuous in the mass, yet the perturbative expansion exhibits a discontinuity in the leading order and singularities in higher orders as in the four-dimensional case. Based on exact cosmological solutions of the model we argue that the helicity-zero graviton state responsible for the perturbative discontinuity decouples from the matter in the limit of vanishing graviton mass in the full classical theory.
TL;DR: In this article, the exact renormalization group equation for pure quantum gravity is used to derive the nonperturbative \ensuremath{\beta}-functions for the dimensionless Newton constant and cosmological constant on the theory space spanned by the Einstein-Hilbert truncation.
Abstract: The exact renormalization group equation for pure quantum gravity is used to derive the nonperturbative \ensuremath{\beta}-functions for the dimensionless Newton constant and cosmological constant on the theory space spanned by the Einstein-Hilbert truncation. The resulting coupled differential equations are evaluated for a sharp cutoff function. The features of these flow equations are compared to those found when using a smooth cutoff. The system of equations with a sharp cutoff is then solved numerically, deriving the complete renormalization group flow of the Einstein-Hilbert truncation in $d=4.$ The resulting renormalization group trajectories are classified and their physical relevance is discussed. The nontrivial fixed point which, if present in the exact theory, might render quantum Einstein gravity nonperturbatively renormalizable is investigated for various spacetime dimensionalities.
TL;DR: The existence of an apparent horizon is related to the solution of an unusual boundary-value problem for Poisson's equation in flat space as discussed by the authors, which provides improved estimates of the classical cross section for black hole production and of the mass of the resulting black holes.
Abstract: We investigate the classical formation of a D-dimensional black hole in a high-energy collision of two particles. The existence of an apparent horizon is related to the solution of an unusual boundary-value problem for Poisson's equation in flat space. For a sufficiently small impact parameter, we construct solutions giving such apparent horizons in $D=4.$ These supply improved estimates of the classical cross section for black hole production, and of the mass of the resulting black holes. We also argue that a horizon can be found in a region of weak curvature, suggesting that these solutions are valid starting points for a semiclassical analysis of quantum black hole formation.
TL;DR: In this paper, the thermal properties of QCD with a small quark chemical potential were investigated using a 16(3)x4 lattice and the leading order Taylor expansion of the pseudocritical point about mu=0.
Abstract: We propose a new method to investigate the thermal properties of QCD with a small quark chemical potential mu. Derivatives of quark and gluonic observables with respect to mu are computed at mu=0 for two flavors of p4 improved staggered fermions with ma=0.1,0.2 on a 16(3)x4 lattice, and used to calculate the leading order Taylor expansion in mu of the location of the pseudocritical point about mu=0. This expansion should be well behaved for the small values of mu(q)/T(c)similar to0.1 relevant for BNL RHIC phenomenology, and predicts a critical curve T-c(mu) in reasonable agreement with estimates obtained using exact reweighting. In addition, we contrast the case of isoscalar and isovector chemical potentials, quantify the effect of munot equal0 on the equation of state, and comment on the complex phase of the fermion determinant in QCD with munot equal0.
TL;DR: In this paper, complete one-loop radiative corrections to KK masses in general 5 and 6-dimensional theories were calculated and applied to the example of universal extra dimensions and showed that the radiative correction is essential to any meaningful study of the phenomenology.
Abstract: Extra-dimensional theories contain a number of almost degenerate states at each Kaluza-Klein level. If extra dimensional momentum is at least approximately conserved then the phenomenology of such nearly degenerate states depends crucially on the mass splittings between KK modes. We calculate the complete one-loop radiative corrections to KK masses in general 5 and 6 dimensional theories. We apply our formulae to the example of universal extra dimensions and show that the radiative corrections are essential to any meaningful study of the phenomenology. Our calculations demonstrate that Feynman diagrams with loops wrapping the extra dimensions are well-defined and cut-off independent even though higher dimensional theories are not renormalizable.
TL;DR: In this paper, the authors explore the possibility of a scalar field with a Lagrangian acting as both clustered dark matter and smoother dark energy and having a scale-dependent equation of state.
Abstract: Cosmological observations suggest the existence of two different kinds of energy densities dominating at small $(\ensuremath{\lesssim}500\mathrm{Mpc})$ and large $(\ensuremath{\gtrsim}1000\mathrm{Mpc})$ scales. The dark matter component, which dominates at small scales, contributes ${\ensuremath{\Omega}}_{m}\ensuremath{\approx}0.35$ and has an equation of state $p=0,$ while the dark energy component, which dominates at large scales, contributes ${\ensuremath{\Omega}}_{V}\ensuremath{\approx}0.65$ and has an equation of state $p\ensuremath{\simeq}\ensuremath{-}\ensuremath{\rho}.$ It is usual to postulate weakly interacting massive particles (WIMPs) for the first component and some form of scalar field or cosmological constant for the second component. We explore the possibility of a scalar field with a Lagrangian $L=\ensuremath{-}V(\ensuremath{\varphi})\sqrt{1\ensuremath{-}{\ensuremath{\partial}}^{i}\ensuremath{\varphi}{\ensuremath{\partial}}_{i}\ensuremath{\varphi}}$ acting as both clustered dark matter and smoother dark energy and having a scale-dependent equation of state. This model predicts a relation between the ratio $r={\ensuremath{\rho}}_{V}/{\ensuremath{\rho}}_{\mathrm{DM}}$ of the energy densities of the two dark components and an expansion rate n of the universe [with $a(t)\ensuremath{\propto}{t}^{n}]$ in the form $n=(2/3)(1+r).$ For $r\ensuremath{\approx}2,$ we get $n\ensuremath{\approx}2$ which is consistent with observations.
TL;DR: In this paper, the authors provide an analytic method to discriminate among different types of black holes on the ground of their strong field gravitational lensing properties, and apply this general formalism to Schwarzschild, Reissner-Nordstrom and Janis-Newman-Winicour black holes.
Abstract: We provide an analytic method to discriminate among different types of black holes on the ground of their strong field gravitational lensing properties. We expand the deflection angle of the photon in the neighbourhood of complete capture, defining a strong field limit, in opposition to the standard weak field limit. This expansion is worked out for a completely generic spherically symmetric spacetime, without any reference to the field equations and just assuming that the light ray follows the geodesics equation. We prove that the deflection angle always diverges logarithmically when the minimum impact parameter is reached. We apply this general formalism to Schwarzschild, Reissner-Nordstrom and Janis-Newman-Winicour black holes. We then compare the coefficients characterizing these metrics and find that different collapsed objects are characterized by different strong field limits. The strong field limit coefficients are directly connected to the observables, such as the position and the magnification of the relativistic images. As a concrete example, we consider the black hole at the centre of our galaxy and estimate the optical resolution needed to investigate its strong field behaviour through its relativistic images.
TL;DR: In this article, the de Sitter/conformal field theory (dS/CFT) correspondence is illuminated through an analysis of massive scalar field theory in d-dimensional deSitter space, and a density matrix is constructed by tracing out over modes which are causally inaccessible to a single geodesic observer.
Abstract: The de Sitter/conformal field theory (dS/CFT) correspondence is illuminated through an analysis of massive scalar field theory in d-dimensional de Sitter space. We consider a one-parameter family of dS-invariant vacua related by Bogolyubov transformations and compute the corresponding Green functions. It is shown that none of these Green functions correspond to the one obtained by analytic continuation from AdS. Among this family of vacua are in (out) vacua which have no incoming (outgoing) particles on ${\mathcal{I}}^{\ensuremath{-}}$ $({\mathcal{I}}^{+}).$ Surprisingly, it is shown that in odd spacetime dimensions the in and out vacua are the same, implying the absence of particle production for this state. The correlators of the boundary CFT, as defined by the dS/CFT correspondence, are shown to depend on the choice of vacuum state---the correlators with all points on ${\mathcal{I}}^{\ensuremath{-}}$ vanish in the in vacuum. For ${\mathrm{dS}}_{3}$ we argue that this bulk vacuum dependence of the correlators is dual to a deformation of the boundary ${\mathrm{CFT}}_{2}$ by a specific marginal operator. It is also shown that Witten's nonstandard de Sitter inner product (slightly modified) reduces to the standard inner product of the boundary field theory. Next we consider a scalar field in the Kerr-${\mathrm{dS}}_{3}$ Euclidean vacuum. A density matrix is constructed by tracing out over modes which are causally inaccessible to a single geodesic observer. This is shown to be a thermal state at the Kerr-${\mathrm{dS}}_{3}$ temperature and angular potential. It is further shown that, assuming Cardy's formula, the microscopic entropy of such a thermal state in the boundary CFT precisely equals the Bekenstein-Hawking value of one-quarter the area of the Kerr-${\mathrm{dS}}_{3}$ horizon.
TL;DR: In this paper, the authors present a new contracting background model (neither of Pre-Big-Bang nor of the Ekpyrotic form) involving a single scalar field coupled to gravity in which a scale invariant spectrum of curvature fluctuations and gravitational waves results.
Abstract: In Pre-Big-Bang and in Ekpyrotic Cosmology, perturbations on cosmological scales today are generated from quantum vacuum fluctuations during a phase when the Universe is contracting (viewed in the Einstein frame). The backgrounds studied to date do not yield a scale invariant spectrum of adiabatic fluctuations. Here, we present a new contracting background model (neither of Pre-Big-Bang nor of the Ekpyrotic form) involving a single scalar field coupled to gravity in which a scale-invariant spectrum of curvature fluctuations and gravitational waves results. The equation of state of this scalar field corresponds to cold matter. We demonstrate that if this contracting phase can be matched via a nonsingular bounce to an expanding Friedmann cosmology, the scale-invariance of the curvature fluctuations is maintained. We also find new background solutions for Pre-Big-Bang and for Ekpyrotic cosmology, which involve two scalar fields with exponential potentials with background values which are evolving in time. We comment on the difficulty of obtaining a scale-invariant spectrum of adiabatic fluctuations with background solutions which have been studied in the past.
TL;DR: In this article, the boundary stress tensor and charges of asymptotically de Sitter (dS) spacetimes were computed from data at early or late time infinity.
Abstract: We propose a novel prescription for computing the boundary stress tensor and charges of asymptotically de Sitter (dS) spacetimes from data at early or late time infinity If there is a holographic dual to dS spaces, defined analogously to the AdS/CFT correspondence, our methods compute the (Euclidean) stress tensor of the dual We compute the masses of Schwarzschild-de Sitter black holes in four and five dimensions, and the masses and angular momenta of Kerr-de Sitter spaces in three dimensions All these spaces are less massive than de Sitter, a fact which we use to qualitatively and quantitatively relate de Sitter entropy to the degeneracy of possible dual field theories Our results in general dimension lead to a conjecture: Any asymptotically de Sitter spacetime with mass greater than de Sitter has a cosmological singularity Finally, if a dual to de Sitter exists, the trace of our stress tensor computes the RG equation of the dual field theory Cosmological time evolution corresponds to RG evolution in the dual The RG evolution of the c function is then related to changes in accessible degrees of freedom in an expanding universe
TL;DR: In this paper, the influence of trans-Planckian physics on the CMBR anisotropies produced by inflation is considered and a simple toy model that allows for analytic calculations is presented.
Abstract: In this paper we consider the influence of trans-Planckian physics on the CMBR anisotropies produced by inflation. We consider a simple toy model that allows for analytic calculations and argue on general grounds, based on ambiguities in the choice of vacuum, that effects are expected with a magnitude of the order of $H/\ensuremath{\Lambda},$ where H is the Hubble constant during inflation and \ensuremath{\Lambda} the scale for new physics, e.g., the Planck scale.
TL;DR: In this paper, it was shown that S(kappa) is the unique existing entropy obtained by a continuous deformation of S0 and preserving unaltered its fundamental properties of concavity, additivity, and extensivity.
Abstract: In Ref. [Physica A 296, 405 (2001)], starting from the one parameter deformation of the exponential function exp(kappa)(x)=(sqrt[1+kappa(2)x(2)]+kappax)(1/kappa), a statistical mechanics has been constructed which reduces to the ordinary Boltzmann-Gibbs statistical mechanics as the deformation parameter kappa approaches to zero. The distribution f=exp(kappa)(-beta E+betamu) obtained within this statistical mechanics shows a power law tail and depends on the nonspecified parameter beta, containing all the information about the temperature of the system. On the other hand, the entropic form S(kappa)= integral d(3)p(c(kappa) f(1+kappa)+c(-kappa) f(1-kappa)), which after maximization produces the distribution f and reduces to the standard Boltzmann-Shannon entropy S0 as kappa-->0, contains the coefficient c(kappa) whose expression involves, beside the Boltzmann constant, another nonspecified parameter alpha. In the present effort we show that S(kappa) is the unique existing entropy obtained by a continuous deformation of S0 and preserving unaltered its fundamental properties of concavity, additivity, and extensivity. These properties of S(kappa) permit to determine unequivocally the values of the above mentioned parameters beta and alpha. Subsequently, we explain the origin of the deformation mechanism introduced by kappa and show that this deformation emerges naturally within the Einstein special relativity. Furthermore, we extend the theory in order to treat statistical systems in a time dependent and relativistic context. Then, we show that it is possible to determine in a self consistent scheme within the special relativity the values of the free parameter kappa which results to depend on the light speed c and reduces to zero as c--> infinity recovering in this way the ordinary statistical mechanics and thermodynamics. The statistical mechanics here presented, does not contain free parameters, preserves unaltered the mathematical and epistemological structure of the ordinary statistical mechanics and is suitable to describe a very large class of experimentally observed phenomena in low and high energy physics and in natural, economic, and social sciences. Finally, in order to test the correctness and predictability of the theory, as working example we consider the cosmic rays spectrum, which spans 13 decades in energy and 33 decades in flux, finding a high quality agreement between our predictions and observed data.
TL;DR: In this paper, the modular invariant one-loop partition function is computed for a two-dimensional cosmological model with a collapsing, an intermediate and an expanding phase, where the boundary between the collapsing phase and the intermediate phase is seen by comoving observers as a cosmologically past horizon.
Abstract: We consider new cosmological solutions with a collapsing, an intermediate and an expanding phase. The boundary between the expanding (collapsing) phase and the intermediate phase is seen by comoving observers as a cosmological past (future) horizon. The solutions are naturally embedded in string and M theory. In the particular case of a two-dimensional cosmology, space-time is flat with an identification under boost and translation transformations. We consider the corresponding string theory orbifold and calculate the modular invariant one-loop partition function. In this case there is a strong parallel with the BTZ black hole. The higher dimensional cosmologies have a timelike curvature singularity in the intermediate region. In some cases the string coupling can be made small throughout all of space-time but string corrections become important at the singularity. This happens where string winding modes become light which could resolve the singularity. The new proposed space-time causal structure could have implications for cosmology, independently of string theory.
TL;DR: In this article, the authors define a minimal model with universal extra dimensions and begin to study its phenomenology, showing that the collider signals of the first Kaluza-Klein (KK) level are surprisingly similar to those of a supersymmetric model with a nearly degenerate superpartner spectrum.
Abstract: We define a minimal model with universal extra dimensions, and begin to study its phenomenology. The collider signals of the first Kaluza-Klein (KK) level are surprisingly similar to those of a supersymmetric model with a nearly degenerate superpartner spectrum. The lightest KK particle (LKP) is neutral and stable because of KK parity. KK excitations cascade decay to the LKP yielding missing energy signatures with relatively soft jets and leptons. Level 2 KK modes may also be probed via their KK number violating decays to standard model particles. In either case we provide initial estimates for the discovery potential of the Fermilab Tevatron and the CERN Large Hadron Collider.