119359128
Variational Study of the Phase Transition at Finite T in the $\lambda \phi^4 $-Theory
Assuming triviality of the 4-dimensional $\lambda \phi ^4$-theory we compute the effective potential by means of a self consistent Feynman-Bogoliubov method. This potential $U_{eff}^{FB}$ depends on a UV-cutoff, which is fixed by a stability condition for the gap-equation for the plasma mass. It shows a second order phase transition at zero temperature, in agreement with a large amount of analytical and RG analysis as well as Monte Carlo numerical evidence. As the cutoff $\Lambda $ is removed the renormalized self coupling constant $\lambda _R$ goes to zero consistent with the claim of triviality. At finite temperature the phase transition becomes weakly first order.
119486225
Resonance enhancement of particle production during reheating
We found a consistent equation of reheating after inflation which shows that for small quantum fluctuations the frequencies of resonance are slighted different from the standard ones. Quantum interference is taken into account and we found that at large fluctuations the process mimics very well the usual parametric resonance, but proceeds in a different dynamical way. The analysis is made in a toy quantum mechanical model and we discuss further its extension to quantum field theory.
121231484
Interference in the radiation of two relativistic charges
The radiation produced by two interacting relativistic point charges is considered. Under an appropriate approximation the radiation of the system as a whole (interference effects included) is expressed as a function of the relative velocity.
8354557
Cluster Algorithm Renormalization Group Method
We present a self consistent method based on cluster algorithms and Renormalization Group on the lattice to study critical systems numerically. We ill ustrate it by means of the 2D Ising model. We compute the critical exponents ν and η and the renormalization group flow of the probability density function of the magnetization. The results, compared to the standard Monte Carlo Renormalization Group proposed by Swendsen [1], are very accurate and the method works faster by a factor which grows monotonically with the lattice size. This allows to simulate larger lattices in reachable computational times.
118167913
Analytical computation of the magnetization probability density function for the harmonic 2D XY model
The probability density function (PDF) of some global average quantity plays a fundamental role in critical and highly correlated systems. We explicitly compute this quantity as a function of the magnetization for the two dimensional XY model in its harmonic approximation. Numerical simulations and perturbative results have shown a Gumbel-like shape of the PDF, in spite of the fact that the average magnetization is not an extreme variable. Our analytical result allows to test both perturbative analytical expansions and also numerical computations performed previously. Perfect agreement is found for the first moments of the PDF. Also for large volume and in the high temperature limit the distribution becomes Gaussian, as it should be. In the low temperature regime its numerical evaluation is compatible with a Gumbel distribution.
119832693
Renormalized loop expansion to compute finite size effects of the constraint effective potential
In latticeφ4 close to the critical line, finite size effects can be computed by renormalized loop expansions. In order to do so, the constraint effective potential is computed to two loop order. Using this expression, we are able to extract results for renormalized masses and coupling constants from Multigrid Monte Carlo data of Mack and Meyer for the constraint effective potential close to the critical line, and compare them with the analytical results ofLüscher and Weisz. Perfect agreement is found.
15031265
On Newton's law in supersymmetric braneworld models
We study the propagation of gravitons within 5-D supersymmetric braneworld models with a bulk scalar field. The setup considered here consists of a 5-D bulk spacetime bounded by two 4-D branes localized at the fixed points of an S1/2 orbifold. There is a scalar field in the bulk which, given a superpotential W(), determines the warped geometry of the 5-D spacetime. This type of scenario is common in string theory, where the bulk scalar field is related to the volume of small compact extra dimensions. We show that, after the moduli are stabilized by supersymmetry breaking terms localized on the branes, the only relevant degrees of freedom in the bulk consist of a 5-D massive spectrum of gravitons. Then we analyze the gravitational interaction between massive bodies localized at the positive tension brane mediated by these bulk gravitons. It is shown that the Newtonian potential describing this interaction picks up a non-trivial contribution at short distances that depends on the shape of the superpotential W(). We compute this contribution for dilatonic braneworld scenarios W() eα (where α is a constant) and discuss the particular case of 5-D Heterotic M-theory: It is argued that a specific footprint at micron scales could be observable in the near future.
118478824
A non-perturbative argument for the non-abelian Higgs mechanism
Abstract The evasion of massless Goldstone bosons by the non-abelian Higgs mechanism is proved by a non-perturbative argument in the local BRST gauge.
199684483
LOOP QUANTUM GRAVITY AND ULTRA HIGH ENERGY COSMIC RAYS
A device for introducing particles into an analyzer of dustiness of a gaseous medium comprises a cell having a transparent cover with a microscope arranged thereabove. A through guide duct is made in a wall of the cell, while provided in the bottom of the latter are a vertical feed duct communicating with the dustiness analyzer and a horizontal channel which is an extension of the through guide duct and intersects the vertical feed duct. The device also comprises a source of a pure gaseous medium which is fed under pressure into the through guide duct wherewith the source communicates.
31013176
Effective theories of single field inflation when heavy fields matter
We compute the low energy effective field theory (EFT) expansion for single-field inflationary models that descend from a parent theory containing multiple other scalar fields. By assuming that all other degrees of freedom in the parent theory are sufficiently massive relative to the inflaton, it is possible to derive an EFT valid to arbitrary order in perturbations, provided certain generalized adiabaticity conditions are respected. These conditions permit a consistent low energy EFT description even when the inflaton deviates off its adiabatic minimum along its slowly rolling trajectory. By generalizing the formalism that identifies the adiabatic mode with the Goldstone boson of this spontaneously broken time translational symmetry prior to the integration of the heavy fields, we show that this invariance of the parent theory dictates the entire non-perturbative structure of the descendent EFT. The couplings of this theory can be written entirely in terms of the reduced speed of sound of adiabatic perturbations. The resulting operator expansion is distinguishable from that of other scenarios, such as standard single inflation or DBI inflation. In particular, we re-derive how certain operators can become transiently strongly coupled along the inflaton trajectory, consistent with slow-roll and the validity of the EFT expansion, imprinting features in the primordial power spectrum, and we deduce the relevant cubic operators that imply distinct signatures in the primordial bispectrum which may soon be constrained by observations. We dedicate this paper to the memory of our dear colleague and friend, Sjoerd Hardeman. His ideas, insights and diligence permeates every aspect of this work.
118586772
Features of heavy physics in the CMB power spectrum
The computation of the primordial power spectrum in multi-field inflation models requires us to correctly account for all relevant interactions between adiabatic and non-adiabatic modes around and after horizon crossing. One specific complication arises from derivative interactions induced by the curvilinear trajectory of the inflaton in a multi-dimensional field space. In this work we compute the power spectrum in general multi-field models and show that certain inflaton trajectories may lead to observationally significant imprints of `heavy' physics in the primordial power spectrum if the inflaton trajectory turns, that is, traverses a bend, sufficiently fast (without interrupting slow roll), even in cases where the modes normal to the trajectory have masses approaching the cutoff of our theory. We emphasize that turning is defined with respect to the geodesics of the sigma model metric, irrespective of whether this is canonical or non-trivial. The imprints generically take the form of damped superimposed oscillations on the power spectrum. In the particular case of two-field models, if one of the fields is sufficiently massive compared to the scale of inflation, we are able to compute an effective low energy theory for the adiabatic mode encapsulating certain relevant operators of the full multi-field dynamics. As expected, a particular characteristic of this effective theory is a modified speed of sound for the adiabatic mode which is a functional of the background inflaton trajectory and the turns traversed during inflation. Hence in addition, we expect non-Gaussian signatures directly related to the features imprinted in the power spectrum.