============================================================================ Date: Thursday, September 4, 2003 Time: 3:55 PM EST Submitted by: Hael Collins Email address: hcollins@andrew.cmu.edu Subject: dS Days Abstract Submission title: The fate of the alpha-vacuum abstract: de Sitter space-time has a one complex parameter family of invariant vacua for the theory of a free, massive scalar field. For most of these vacua, in an interacting scalar theory the one loop corrections diverge linearly for large values of the loop momentum. These divergences are not of a form that can be removed by a de Sitter invariant counterterm, except in the case of the Euclidean, or Bunch-Davies, vacuum. refs: hep-th/0306028 section: Initial conditions/Imprint of new physics ============================================================================ Date: Sunday, September 7, 2003 Time: 3:50 PM EST Submitted by: Atsushi Higuchi Email address: ah28@york.ac.uk Subject: dS Days Abstract Submission title: Long-distance behaviour of the graviton propagator abstract: First I will review implications of quantum linearization instabilities found by Moncrief on linearized gravity in de Sitter spacetime. In particular, I will point out that all physical states in linearized gravity are required to be de Sitter invariant. An approach to resolve this apparent paradox will be presented. Then, assuming that the usual massless spin-2 theory in the de Sitter background is relevant in studying linearized gravity --- which seems likely --- I will discuss the long-distance behaviour of the graviton two-point functions (1) in a two-parameter family of covariant gauges, (2) in a Coulomb-like gauge with flat spatial sections and (3) in a Coulomb-like gauge with S^3 spatial sections. I will show that their logarithmic growth as a function of the coordinate distance of the two points in the first two cases found in the literature is a gauge artifact. Then I will show that the two-point function does not grow in the third case. I will also demonstrate that the conformal sector in the covariant gauges can be made to vanish by a choice of gauge parameters, that the mass of the modes in this sector is gauge-dependent, and hence that no physical effect is expected from this sector, contrary to some claims made in the literature. refs: CQG 8 (1991) 1983-2004; gr-qc/0004079; gr-qc/0011062; gr-qc/0107036; gr-qc/0212031. section: Stability/Backreaction of fluctuations ============================================================================ Date: Monday, September 8, 2003 Time: 2:10 PM EST Submitted by: Matthew Martin Email address: mmartin@cmu.edu Subject: dS Days Abstract Submission title: Vacuum selection and the enhancement of inflaton loops abstract: In a truncated version of the alpha-vacuum, loop effects are enhanced by powers of the truncation scale over the Hubble scale. We demonstrate this explicitly in the calculation of the power spectrum and discuss the importance for models of Planck scale physics using modified vacuum states. refs: H. Collins and M. R. Martin, to appear soon section: Initial conditions/Imprint of new physics ============================================================================ Date: Saturday, September 13, 2003 Time: 2:43 PM EST Submitted by: Richard Woodard Email address: woodard@phys.ufl.edu Subject: dS Days Abstract Submission title: Post-Inflationary Dynamics abstract: I present recent work with Nick Tsamis, some of which is described in astro-ph/0303175. We now have a stochastic formulation of quantum gravity which explicitly confirms previous perturbative calculations showing that the back- reaction from graviton production slows inflation by an amount that eventually becomes non-perturbatively strong. The new, stochastic formulation permits one to follow this process into the non-perturbative regime where inflation is not only halted but the universe actually enters a brief phase of deflation. This deflationary period ends with the creation of a hot, dense thermal barrier that scatters the infrared gravitons needed to propagate the quantum correlations forward from the epoch of inflationary particle production. Subsequent evolution is controlled by the balance between the persistence of the thermal barrier and the growth in the 4-volume of inflationary spacetime which is causally related to a post-inflationary observer. refs: hep-ph/0303175 section: Stability/Backreaction of fluctuations ============================================================================ ============================================================================ Date: Monday, September 15, 2003 Time: 11:30 AM EST Submitted by: Arjun Berera Email address: ab@ph.ed.ac.uk Subject: dS Days Abstract Submission title: Warm inflation is natural abstract: There are two types of inflation dynamics, isentropic or cold inflation and nonisentropic or warm inflation. In the former inflation occurs without radiation production, whereas in the latter both radiation production and inflation occur concurrently. In this talk I show that warm inflation has intrinsic model independent features that makes it natural or equivalently have no ``eta problem''. I then discuss the quantum field theory dynamics underlying warm inflation and show that in very simple models, radiation production occurs concurrently with inflation, thus realizing warm inflation. These models, in particular include certain regimes of multifield inflation models, like hybrid inflation, which up to now were assumed to yield exclusivly cold inflation. Finally denisty perturbations and observational consequences of warm inflation are discussed. refs: e.g. hep-ph/0308211; Phys. Lett. B567, 294 (2003). section: Stability/Backreaction of fluctuations, Initial conditions/Imprint of new physics ============================================================================ Date: Tuesday, September 23, 2003 Time: 4:42 PM EST Submitted by: Leonard Parker Email address: leonard@uwm.edu Subject: dS Days Abstract Submission title: Acceleration of Universe from Heat Kernel Asymptotics abstract: The large-time asymptotic form of the heat kernel is studied in an expanding universe.This asymptotic form for a quantized scalar field of mass m can accelerate the expansion of the universe. For large m this effect may be relevant to early inflation, while for small m it may be relevant to the presently observed acceleration of the universe. This conclusion is supported by numerical solutions of the semiclassical Einstein equations. refs: PRD 60 (1999) 063512; Ap J 588 (2003) 663; and paper in preparation section: Stability/Backreaction of fluctuations, Strings and de Sitter ============================================================================ ============================================================================ Date: Thursday, September 25, 2003 Time: 6:27 AM EST Submitted by: Tomislav Prokopec Email address: T.Prokopec@thphys.uni-heidelberg.de Subject: dS Days Abstract Submission title: Production of Massless Fermions during Inflation abstract: We compute the one loop self energy, in a locally de Sitter background, for a massless fermion which is Yukawa-coupled to a massless, minimally coupled scalar. We then solve the modified Dirac equation resulting from inclusion of the self energy. We find faster-than-exponential growth in the fermion wave function, consistent with the production of fermions through a process in which a scalar and a fermion- anti-fermion pair are ripped out of the vacuum by inflation. refs: astro-ph/0309593 ============================================================================ ============================================================================ Date: Saturday, September 27, 2003 Time: 6:09 PM EST Submitted by: Anupam Mazumdar Email address: anupamm@hep.physics.mcgill.ca Subject: dS Days Abstract Submission title: Instantons and their role in cosmological constant abstract: I will discuss the role of non-abelian theory and its contribution to dressed cosological constant. I will also describe why now and the cosmological constant is a demanding problem to understand and why it is so small. I will also try to seek how can we test such paradigms. refs: section: Initial conditions/Imprint of new physics ============================================================================ ============================================================================ Date: Tuesday, September 30, 2003 Time: 12:23 AM EST Submitted by: Daniel J H Chung Email address: danielchung@wisc.edu Subject: dS Days Abstract Submission title: Theoretical Uncertainties of the Standard Inflationary Vacuum abstract: We discuss the minimal theoretical uncertainty in inflationary curvature fluctuations due to the nonuniqueness of the vacuum, even in the absence of any trans-Planckian uncertainties or effective field theory cutoff related effects. refs: hep-ph/0305074 section: Initial conditions/Imprint of new physics ============================================================================ ============================================================================ Date: Thursday, October 2, 2003 Time: 4:36 AM EST Submitted by: Fabio Finelli Email address: finelli@bo.iasf.cnr.it Subject: dS Days Abstract Submission title: Energy-Momentum Tensor of Cosmological Fluctuations in Massive Chaotic Inflation abstract: The renormalized energy-momentum tensor (EMT) of cosmological fluctuations is computed in a model of chaotic inflation driven by a massive field. We find that the renormalized EMT carries negative energy density and has a de Sitter-like equation of state. We compute its back-reaction on the background inflationary trajectory through second-order perturbation theory. refs: PRD 65 (2002) 103521 and paper to appear section: Stability/Backreaction of fluctuations ============================================================================ ============================================================================ Date: Thursday, October 2, 2003 Time: 10:53 AM EST Submitted by: Johannes Martin Email address: jmartin@cita.utoronto.ca Subject: dS Days Abstract Submission title: Branedynamics abstract: The full nonlinear treatment of the evolution of brane systems have sofar been lying beyond the scope of analytical methods. Nevertheless it is important to understand their dynamics if one wants to address problems of brane inflation, graceful exit from inflation, Radion stabilization and the cosmological constant. We have investigated the numerical solutions of a Two-Brane system with bulk scalar field in the framework of General Relativity. We were able to recover static brane solutions and to analyse their stability. Furtherone we discovered interpolating solutions between two different Hubble scales, which can give first hints for a cosmological evolution with deSitter-Branes, as well as analytic solutions for the regime of brane collision. refs: e.g. hep-th/0309001 section: Strings and de Sitter ============================================================================ Hi Patrick. I'm planning to come to the workshop at Fermilab (I've already registered). If there is a slot available, I would like to give a talk, based on papers that we are doing in Toronto. I write below the title/abstract. Greetings, Marco Title: De Sitter branes and the gravi/scalar nature of the radion Abstract: We report the results of a series of works dealing with inflating branes in extra dimensional models. Inflating branes are more difficult to stabilize than flat ones. Still, specific models can be constructed so that the system is stable. For example, this can be done by bulk scalar field(s) with appropriate bulk/brane potentials, in analogy with the Goldberger-Wise mechanism for flat branes. This scenario can provide a new mechanism for the generation of primordial scalar perturbations on the brane, namely {\it induced metric perturbations}. Bulk metric perturbations are coupled to fluctuations of the bulk field. The identification of the physical modes requires diagonalization and quantization of the coupled system. The radion field is the lightest of these physical modes. In the case of flat branes, it is typically assumed that metric and scalar perturbations are weakly coupled, so that a proper diagonalization is not in order. We show that this is not the case, and that the properties of the radion field turn out to be very different from the ones which have been known so far. Phenomenological constraints on braneworld models should be changed accordingly. ============================================================================ Date: Wednesday, October 8, 2003 Time: 10:09 PM EST Submitted by: Emil Martinec Email address: ejm@theory.uchicago.edu Subject: dS Days Abstract Submission title: Having the World on a String abstract: Two dimensional (Liouville) gravity models higher dimensional de Sitter cosmology with surprising fidelity, and yet is an exactly solvable quantum field theory. Suitable coupling to matter yields models of inflation, opening new possibilities to explore structure formation, initial conditions, etc, while including the effects of quantum gravitational back-reaction. One may also explore the relation between quantum gravity and thermodynamics in this context; some additional possible applications are also described. refs: hep-th/0303087 and hep-th/0305148 section: Strings and de Sitter ============================================================================ ============================================================================ Date: Friday, October 10, 2003 Time: 5:33 PM EST Submitted by: S Khlebnikov Email address: skhleb@physics.purdue.edu Subject: dS Days Abstract Submission title: A dual description of decoherence in de Sitter space abstract: Decoherence associated with super-Hubble modes in de Sitter space may have a dual description, in which it is attributed to interaction of sub-Hubble modes with an ``environment'' residing just inside the observer's horizon. We present a version of such description, together with some consistency checks, which it is shown to pass. refs: JHEP 0303, 059, 2003 [hep-th/0301103] section: Holography/UV-IR Correspondence ============================================================================ ============================================================================ Date: Friday, October 10, 2003 Time: 10:40 PM EST Submitted by: David Lowe Email address: lowe@brown.edu Subject: dS Days Abstract Submission title: Alpha-vac perturbation theory abstract: Alpha-vacua in interacting field theory can be defined in several different ways. We show how these approaches are related, and elaborate on one approach which leads to a consistent renormalizable perturbative expansion around a fixed de Sitter background. Nevertheless, we argue even this approach fails when coupling to gravity is taken into account. The Bunch-Davies vacuum is singled out as the unique de Sitter invariant state that can be consistently coupled to gravity at the non-perturbative level. refs: hep-th/0308135, hep-th/0302050 section: Initial conditions/Imprint of new physics ============================================================================ ============================================================================ Date: Thursday, October 23, 2003 Time: 10:58 AM EST Submitted by: Stefan Hollands Email address: stefan@gr.uchicago.edu Subject: dS Days Abstract Submission title: Alpha-vacua ruled out by general covariance abstract: The linear massive scalar field in deSitter space admits a 1-parameter family of quantum states invariant under the deSitter group, the ``$\alpha$-vacua''. Among these states, one is distinguished, but the other $\alpha$-vacua also have been considered recently in the context of cosmological applications. We argue these other $\alpha$-vacua are not acceptable if one wants to consider observables that are nonlinear in the field, such as the Wick-powers of the field, or their time ordered products. Based on recent progress in the formulation of interacting quantum field theories in curved spacetimes, we prove that the other $\alpha$-vacua are necessarily ill-defined on non-linear field observables, if the latter satsify the following assumptions: (a) The Wick-powers and time ordered products are local and generally covariant (and in particular, can be defined for {\em all} spacetimes, (b) their definition conicides with the familiar definition in Minkowski spacetime. Thus, in this sense, the other $\alpha$-vacua are forbidden by general covariance. refs: ============================================================================ ============================================================================ Date: Monday, October 27, 2003 Time: 12:22 AM EST Submitted by: Andrei Frolov Email address: afrolov@stanford.edu Subject: dS Days Abstract Submission title: Can Inflating Braneworlds be Stabilized? abstract: We investigate scalar perturbations from inflation in braneworld cosmologies with extra dimensions. Assuming that the inflating branes are stabilized (by the brane scalar field potentials), we estimate the lowest eigenvalue of the scalar fluctuations - the radion mass. We find that for de Sitter (inflating) branes the square of the radion mass can be negative, which leads to a strong tachyonic instability. The presence of the instability is confirmed directly by numerical calculations of the full non-linear braneworld evolution. Thus, parameters of stabilized inflating braneworlds must be constrained to avoid this tachyonic instability. refs: hep-th/0309001, hep-th/0309002 section: Stability/Backreaction of fluctuations ============================================================================ ============================================================================ Date: Monday, October 27, 2003 Time: 8:30 PM EST Submitted by: Kenji Kadota Email address: kadota@socrates.berkeley.edu Subject: dS Days Abstract Submission title: A resolution for initial-condition/fine-tuning problems in modular cosmology abstract: I shall discuss that a moduli space of the form predicted by string theory, lifted by supersymmetry breaking, gives rise to successful inflationary scenario for large regions of parameter space without initial condition or fine-tuning problems. This natural realization of inflation relies crucially on the complex nature of the moduli fields and the multiple points of enhanced symmetry, which are generic features of moduli space but not usually considered in inflationary model building. As an illustration of this scenario, detailed discussion on the modular inflationary scenario induced by non-slow-roll single modulus field will be given. I shall also discuss its definite predictions in its characteristic features imprinted in CMB spectrum. refs: JHEP 0307:013,2003 section: Initial conditions/Imprint of new physics ============================================================================ ============================================================================ Date: Tuesday, October 28, 2003 Time: 10:21 PM EST Submitted by: Ghazal Geshnizjani Email address: geshnizjani@physics.brown.edu Subject: dS Days Abstract Submission title: Back-Reaction of Cosmological Perturbations on a Local Measure of the Expansion abstract: We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the local expansion rate of the Universe. First, we consider a cosmological model in which matter is described by a single field. We analyze back reaction in a phase of scalar field-driven chaotic inflation. We find that the leading infrared terms contributing to the back reaction vanish when the local expansion rate is measured at either a fixed value of the scalar field, which is used as a clock or fixed value of proper time. Then we use coarse-grained method to calculate the additional effect due to the exit of modes from Hubble radios on proper time surfaces and we find that back-reaction effects don’t vanish anymore. We also analyze back reaction in a phase of scalar field-driven chaotic inflation for two scalar field models and we find that it can be quite significant for inflation. refs: hep-th/0310265 section: Stability/Backreaction of fluctuations ============================================================================ ============================================================================ Date: Wednesday, October 29, 2003 Time: 5:12 AM EST Submitted by: MARTIN Jerome Email address: jmartin@iap.fr Subject: dS Days Abstract Submission title: Parametric amplification of metric fluctuations through a bouncing phase abstract: We clarify the properties of the behavior of classical cosmological perturbations when the Universe experiences a bounce. This is done in the simplest possible case for which gravity is described by general relativity and the matter content has a single component, namely a scalar field in a closed geometry. We show in particular that the spectrum of scalar perturbations can be affected by the bounce in a way that may depend on the wave number,even in the large scale limit. This may have important implications for string motivated models of the early Universe. refs: astro-ph/0307077 to appear in PRD section: Stability/Backreaction of fluctuations, Strings and de Sitter ============================================================================ ============================================================================ Date: Wednesday, October 29, 2003 Time: 3:27 PM EST Submitted by: Emil Mottola Email address: emil@lanl.gov Subject: dS Days Abstract Submission title: Allowed States & Stress Tensor Fluctuations in de Sitter Space abstract: The state of a quantum field in de Sitter space is usually limited to the Bunch-Davies `vacuum,' which is more accurately described as a thermally populated state with temperature T=H/2 pi. Relaxing global de Sitter invariace of the Bunch-Davies state to: 1) SO(4,1) invariant `alpha vacua', or 2) SO(4) or spatially homogeneous, isotropic invariant states, or 3) O(3) rotationally invariant states about some origin, lead to different possibilities for physical stress tensor fluctuations in de Sitter space. In the case of the alpha vacua the stress tensor has unphysical UV divergences, except for alpha equal to zero, and should be excluded. The stress tensor for all UV allowed spatially homogeneous, isotropic states approaches the Bunch-Davies (or Allen-Follaci) values at late times. However, the stress tensor for O(3) invariant states which are not populated at precisely the temperature H/2pi diverges at the horizon. The large backreaction effects near the horizon of fluctuations into these allowed states can be probed by linear response. refs: PRD 31, 754 ('85); PRD 33, 1616 ('86); PRD 33, 2136 ('86); NPB 278, 694 ('86); PRD 62, 124019 (2000) section: Stability/Backreaction of fluctuations ============================================================================ ============================================================================ Date: Wednesday, October 29, 2003 Time: 4:08 PM EST Submitted by: Paul R Anderson Email address: anderson@wfu.edu Subject: dS Days Abstract Submission title: Linear Response Theory and the Validity of the Semiclassical Approximation abstract: It will be argued that a useful criterion for the validity of the semiclassical approximation in gravity is that the approximation breaks down if solutions to the semiclassical linear response equations diverge in some gauge invariant sense. It will be shown that a self-consistent linear response analysis based upon an invariant effective action principle involves the two-point correlation function of the quantum energy-momentum tensor. The properties of this correlation function are discussed and it is shown on general grounds that it contains no state-dependent divergences and requires no new renormalization counterterms beyond those required in the leading order semi-classical approximation. The behavior of solutions to the linear response equations in Minkowski space will be discussed and the form that the linear response equations take in de Sitter space in spatially flat coordinates will be derived. refs: PRD 67, 024026 (2003) section: Stability/Backreaction of fluctuations ============================================================================ I have submitted an abstract via your web site and unfortunately found a couple of minor errors in it afterward. If you decide to accept my talk please use the following modified one. Sincerely, Paul Anderson It will be argued that a useful criterion for the validity of the semiclassical approximation in gravity is that the approximation breaks down if solutions to the semiclassical linear response equations diverge in some gauge invariant sense. It will be shown that a self-consistent linear response analysis based upon an invariant effective action principle involves the two-point correlation function of the quantum energy-momentum tensor. The properties of this correlation function will be discussed and it will be shown on general grounds that it contains no state-dependent divergences and requires no new renormalization counterterms beyond those required in the leading order semi-classical approximation. The behavior of solutions to the linear response equations in Minkowski space will be discussed and the form that the linear response equations take in de Sitter space in spatially flat coordinates will be derived. ====================================================================== ============================================================================ Date: Friday, October 31, 2003 Time: 1:09 PM EST Submitted by: Katherine Freese Email address: ktfreese@umich.edu Subject: dS Days Abstract Submission title: What can WMAP tell us about the very early universe? abstract: The Wilkinson Microwave Anisotropy Probe microwave background data may be giving us clues about new physics at the transition from a ``stringy'' epoch of the universe to the standard Friedmann Robertson Walker description. Deviations on large angular scales of the data, as compared to theoretical expectations, as well as running of the spectral index of density perturbations, can be explained by new physics whose scale is set by the height of an inflationary potential. As examples of possible signatures for this new physics, we study the cosmic microwave background spectrum for two string inspired models: 1) modifications to the Friedmann equations and 2) velocity dependent potentials. The suppression of low ``l'' modes in the microwave background data arises due to the new physics. In addition, the spectral index is red (n<1) on small scales and blue (n>1) on large scales, in agreement with data. refs: hep-ph/0306289 section: Initial conditions/Imprint of new physics HI Patrick, I can only speak on Nov. 14 or 15, so please schedule me then. Thanks! Katie ============================================================================ Date: Friday, October 31, 2003 Time: 3:29 PM EST Submitted by: Eugene Lim Email address: elim@oddjob.uchicago.edu Subject: dS Days Abstract Submission title: Constraints on Inflationary Vacuum Choices abstract: We present a generic model of parameterizing the ambiguity in the choice of vacuum for the fluctuations during inflation. We then discuss the constraints imposed on those parameters by the recent WMAP data. refs: hep-th/0303103 section: Initial conditions/Imprint of new physics ============================================================================ ============================================================================ Date: Friday, October 31, 2003 Time: 3:29 PM EST Submitted by: Erick Weinberg Email address: ejw@phys.columbia.edu Subject: dS Days Abstract Submission title: New bounce solutions and vacuum tunneling in de Sitter spacetim abstract: I will describe a new family of bounce solutions. I will then discuss the relevance of these solutions for transitions between vacua and a thermal interpretation of vacuum transitions in de Sitter space. refs: hep-th/0312??? (as a best estimate) ============================================================================ Rocky and Patrick, I just posted an abstract on the web site. In doing the scheduling, could you try to avoid scheduling me for Saturday. In order to make a crucial theater performance (The Laramie Project, co-starring Ms. C. Weinberg), I have to make a 1 PM plane out of O'Hare. Thanks Erick ==============================================================