124 research outputs found

    Causal Boundary Entropy From Horizon Conformal Field Theory

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    The quantum theory of near horizon regions of spacetimes with classical spatially flat, homogeneous and isotropic Friedman-Robertson-Walker geometry can be approximately described by a two dimensional conformal field theory. The central charge of this theory and expectation value of its Hamiltonian are both proportional to the horizon area in units of Newton's constant. The statistical entropy of horizon states, which can be calculated using two dimensional state counting methods, is proportional to the horizon area and depends on a numerical constant of order unity which is determined by Planck scale physics. This constant can be fixed such that the entropy is equal to a quarter of the horizon area in units of Newton's constant, in agreement with thermodynamic considerations.Comment: 11 pages, no figure

    Dark Matter in Models of String Cosmology

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    The origin of dark matter in the universe may be weakly interacting scalar particles produced by amplification of quantum fluctuations during a period of dilaton-driven inflation. We present two interesting cases, the case of small fluctuations, and the resulting nonthermal spectrum, and the case of large fluctuations of a field with a periodic potential, the QCD axion.Comment: 13 pages LaTeX, uses aipproc.sty, talk presented by R. Brustein at COSMO 98, Asilomar, California, November 199

    Classical Corrections in String Cosmology

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    An important element in a model of non-singular string cosmology is a phase in which classical corrections saturate the growth of curvature in a deSitter-like phase with a linearly growing dilaton (an `algebraic fixed point'). As the form of the classical corrections is not well known, here we look for evidence, based on a suggested symmetry of the action, scale factor duality and on conformal field theory considerations, that they can produce this saturation. It has previously been observed that imposing scale factor duality on the O(α′)O(\alpha') corrections is not compatible with fixed point behavior. Here we present arguments that these problems persist to all orders in α′\alpha'. We also present evidence for the form of a solution to the equations of motion using conformal perturbation theory, examine its implications for the form of the effective action and find novel fixed point structure.Comment: 30 pages, Latex, epsfig, 6 figure

    Black hole entropy divergence and the uncertainty principle

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    Black hole entropy has been shown by 't Hooft to diverge at the horizon. The region near the horizon is in a thermal state, so entropy is linear to energy which consequently also diverges. We find a similar divergence for the energy of the reduced density matrix of relativistic and non-relativistic field theories, extending previous results in quantum mechanics. This divergence is due to an infinitely sharp division between the observable and unobservable regions of space, and it stems from the position/momentum uncertainty relation in the same way that the momentum fluctuations of a precisely localized quantum particle diverge. We show that when the boundary between the observable and unobservable regions is smoothed the divergence is tamed. We argue that the divergence of black hole entropy can also be interpreted as a consequence of position/momentum uncertainty, and that 't Hooft's brick wall tames the divergence in the same way, by smoothing the boundary.Comment: Added clarifications and explanation

    Small field models of inflation that predict a tensor-to-scalar ratio r=0.03r=0.03

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    Future observations of the cosmic microwave background (CMB) polarization are expected to set an improved upper bound on the tensor-to-scalar ratio of r≲0.03r\lesssim 0.03. Recently, we showed that small field models of inflation can produce a significant primordial gravitational wave signal. We constructed viable small field models that predict a value of rr as high as 0.010.01. Models that predict higher values of rr are more tightly constrained and lead to larger field excursions. This leads to an increase in tuning of the potential parameters and requires higher levels of error control in the numerical analysis. Here, we present viable small field models which predict r=0.03r=0.03. We further find the most likely candidate among these models which fit the most recent Planck data while predicting r=0.03r= 0.03. We thus demonstrate that this class of small field models is an alternative to the class of large field models. The BICEP3 experiment and the Euclid and SPHEREx missions are expected to provide experimental evidence to support or refute our predictions.Comment: 10 pages, 5 figure
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