Effective Field Theory with a Variable Ultraviolet Cutoff

The properties of strongly gravitating systems suggest that field theory overcounts the states of a system. Reducing the number of degrees of freedom, without abandoning the notion of effective field theory, may be achieved through a connection between the ultraviolet and infrared cutoffs. We provide an implementation of this idea within the Wilsonian approach to the renormalization group. We derive an exact flow equation that describes the evolution of the effective action. We discuss the implications for the existence of infrared fixed points and the running of couplings. We also give an alternative derivation in the context of the perturbative renormalization group.Comment: minor corrections, additional reference

Suppression of Quantum Corrections by Classical Backgrounds

We use heat-kernel techniques in order to compute the one-loop effective action in the cubic Galileon theory for a background that realizes the Vainshtein mechanism. We find that the UV divergences are suppressed relative to the predictions of standard perturbation theory at length scales below the Vainshtein radius.Comment: 10 pages, 1 figure, major revision, inclusion of higher-order terms, version to appear in PR

Anomalous anomalous scaling?

Motivated by speculations about infrared deviations from the standard behavior of local quantum field theories, we explore the possibility that such effects might show up as an anomalous running of coupling constants. The most sensitive probes are presently given by the anomalous magnetic moments of the electron and the muon, that suggest that alpha_{em} runs 1.00047 +- 0.00018 times faster than predicted by the Standard Model. The running of alpha_{em} and alpha_s up to the weak scale is confirmed with a precision at the % level.Comment: 4 page

Exact solutions for Vacuum Decay in Unbounded Potentials

The Standard Model Higgs potential may become unbounded from below at large field values, with important cosmological implications. For a potential of this form, the commonly assumed scenario of a nucleated thin-wall bubble driving the transition from the electroweak vacuum to the unstable region does not apply. We present exact analytical solutions for potentials that have the same qualitative form as the Higgs potential. They show that the transition is driven by a thick-wall spherical bubble of true vacuum, with a surface that expands at asymptotically the speed of light. A `crunch' singularity appears in the quasi-AdS interior, with the collapsed region also expanding at asymptotically the speed of light. The singularity is surrounded by a region of trapped surfaces whose boundary forms an apparent horizon. An event horizon separates the singularity from the bubble exterior, so that the expansion of the bubble surface is not affected by the collapse of the interior. The solutions provide exact descriptions of the geometry for thick-wall bubbles and are consistent with the analysis of [1,2] for the Higgs potential.Comment: 8 pages, 3 figures, some clarifications adde

Nonlinear evolution of density and flow perturbations on a Bjorken background

Density perturbations and their dynamic evolution from early to late times can be used for an improved understanding of interesting physical phenomena both in cosmology and in the context of heavy-ion collisions. We discuss the spectrum and bispectrum of these perturbations around a longitudinally expanding fireball after a heavy-ion collision. The time-evolution equations couple the spectrum and bispectrum to each other, as well as to higher-order correlation functions through nonlinear terms. A non-trivial bispectrum is thus always generated, even if absent initially. For initial conditions corresponding to a model of independent sources, we discuss the linear and nonlinear evolution is detail. We show that, if the initial conditions are sufficiently smooth for fluid dynamics to be applicable, the nonlinear effects are relatively small.Comment: 32 pages, 17 figures, published versio

Backreaction effects on the matter side of Einstein's field equations

Recently, we have derived a novel and compact expression for how perturbations in the matter fields of the cosmological fluid can lead to deviations from the standard Friedmann equations. Remarkably, the dissipative damping of velocity perturbations by bulk and shear viscosity in the dark sector can modify the expansion history of the universe on arbitrarily large scales. In universes in which this effect is sufficiently sizeable, it could account for the acceleration of the cosmological expansion. But even if dark matter should be less viscous and if the effect would be correspondingly smaller, it may have observable consequences in the era of precision cosmology. Here, we review the origin of this backreaction effect and possibilities to constrain it further.Comment: 4 pages, to be published in the Moriond Proceedings 201

Bubble-nucleation rates for cosmological phase transitions

We estimate bubble-nucleation rates for cosmological phase transitions. We concentrate on the evaluation of the pre-exponential factor, for which we give approximate analytical expressions. Our approach relies on the use of a real coarse-grained potential. We show how the coarse-graining scale can be determined in the studies of high-temperature phase transitions. We discuss the metastability bound on the Higgs-boson mass and the electroweak phase transition. We find that the saddle-point approximation is reliable in the first case and breaks down in the second case.Comment: 8 pages, 2 fig.s. Final versio

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.