Flow of the Coarse Grained Free Energy for Crossover Phenomena

The critical behaviour of a system of two coupled scalar fields in three dimensions is studied within the formalism of the effective average action. The fixed points of the system are identified and the crossover between them is described in detail. Besides the universal critical behaviour, the flow of the coarse grained free energy also describes the approach to scaling.Comment: 18 pages, latex, 4 figures appended as uuencoded fil

Coleman-Weinberg Phase Transition in Two-Scalar Models

We explore the Coleman-Weinberg phase transition in regions outside the validity of perturbation theory. For this purpose we study a Euclidean field theory with two scalars and discrete symmetry in four dimensions. The phase diagram is established by a numerical solution of a suitable truncation of exact non-perturbative flow equations. We find regions in parameter space where the phase transition (in dependence on the mass term) is of the second or the first order, separated by a triple point. Our quantitative results for the first order phase transition compare well to the standard perturbative Coleman-Weinberg calculation of the effective potential.Comment: 14 pages, Oxford OUTP 94-14 P, Heidelberg HD-THEP-94-1

Solving non-perturbative flow equations

Non-perturbative exact flow equations describe the scale dependence of the effective average action. We present a numerical solution for an approximate form of the flow equation for the potential in a three-dimensional N-component scalar field theory. The critical behaviour, with associated critical exponents, can be inferred with good accuracy.Comment: Latex, 14 pages, 2 uuencoded figure

Modified brane cosmologies with induced gravity, arbitrary matter content and a Gauss-Bonnet term in the bulk

We extend the covariant analysis of the brane cosmological evolution in order to take into account, apart from a general matter content and an induced-gravity term on the brane, a Gauss-Bonnet term in the bulk. The gravitational effect of the bulk matter on the brane evolution can be described in terms of the total bulk mass as measured by a bulk observer at the location of the brane. This mass appears in the effective Friedmann equation through a term characterized as generalized dark radiation that induces mirage effects in the evolution. We discuss the normal and self-accelerating branches of the combined system. We also derive the Raychaudhuri equation that can be used in order to determine if the cosmological evolution is accelerating.Comment: 12 pages, no figures, RevTex 4.0; (v2) new references are added; (v3,v4) minor changes, acknowledgment is included; to appear in Phys. Rev.

Disoriented and Plastic Soft Terms: A Dynamical Solution to the Problem of Supersymmetric Flavor Violations

We postulate that the orientation of the soft supersymmetry-breaking terms in flavor space is not fixed by tree level physics at the Planck scale; it is a dynamical variable which depends on fields that have no tree level potential. These fields can be thought of as either moduli or as the Nambu-Goldstone bosons of the spontaneously broken flavor symmetry which is non-linearly realized by the soft terms. We show that the soft terms align with the quark and lepton Yukawa couplings, just as spins align with an external magnetic field. As a result, the soft terms conserve individual lepton numbers and do not cause large flavor or CP violations. The vacuum adjusts so as to allow large sparticle splittings to naturally coexist with flavor conservation. Consequently, the resulting phenomenology is different from that of minimal supersymmetric theories. We also propose theories in which the shape of the soft terms in flavor space is a dynamical variable which depends on fields that have no tree level potential. This dynamically leads to partial degeneracy among sparticles and further supression of flavor violations. The ideas of this paper suggest a connection between the space of moduli and the spontaneously broken flavor group.Comment: 16 pages, LATEX, CERN-TH/95-9

Entropy from AdS(3)/CFT(2)

We parametrize the (2+1)-dimensional AdS space and the BTZ black hole with Fefferman-Graham coordinates starting from the AdS boundary. We consider various boundary metrics: Rindler, static de Sitter and FRW. In each case, we compute the holographic stress-energy tensor of the dual CFT and confirm that it has the correct form, including the effects of the conformal anomaly. We find that the Fefferman-Graham parametrization also spans a second copy of the AdS space, including a second boundary. For the boundary metrics we consider, the Fefferman-Graham coordinates do not cover the whole AdS space. We propose that the length of the line delimiting the excluded region at a given time can be identified with the entropy of the dual CFT on a background determined by the boundary metric. For Rindler and de Sitter backgrounds our proposal reproduces the expected entropy. For a FRW background it produces a generalization of the Cardy formula that takes into account the vacuum energy related to the expansion.Comment: major revision with several clarifications and corrections, 22 page

Cosmology from an AdS Schwarzschild black hole via holography

We derive the equations of cosmological evolution from an AdS Schwarzschild black hole via holographic renormalization with appropriate boundary conditions.Comment: 6 page

Late acceleration and w=−1w=-1 crossing in induced gravity

We study the cosmological evolution on a brane with induced gravity within a bulk with arbitrary matter content. We consider a Friedmann-Robertson-Walker brane, invariantly characterized by a six-dimensional group of isometries. We derive the effective Friedmann and Raychaudhuri equations. We show that the Hubble expansion rate on the brane depends on the covariantly defined integrated mass in the bulk, which determines the energy density of the generalized dark radiation. The Friedmann equation has two branches, distinguished by the two possible values of the parameter \ex=\pm 1. The branch with \ex=1 is characterized by an effective cosmological constant and accelerated expansion for low energy densities. Another remarkable feature is that the contribution from the generalized dark radiation appears with a negative sign. As a result, the presence of the bulk corresponds to an effective negative energy density on the brane, without violation of the weak energy condition. The transition from a period of domination of the matter energy density by non-relativistic brane matter to domination by the generalized dark radiation corresponds to a crossing of the phantom divide $w=-1$.Comment: 7 pages, no figures, RevTex 4.0; (v2) new references are added, minor corrections and expanded discussion; (v3) additional comments at the end of section III, minor corrections and several new references are added, to match published version in Phys. Rev.