arXiv subjects
Publications and source records attributed to Marcelo Gleiser.
We study the nonequilibrium growth of a weakly interacting homogeneous Bose gas after a quench from a high-temperature state to a temperature below the Bose-Einstein critical condensation temperature. We quantitatively characterize the departure from thermal equilibrium and observe the presence of two equilibration time scales. The equilibration times are shown to be inversely proportional to the density.
Within first-order phase transitions, we investigate the pre-transitional effects due to the nonperturbative, large-amplitude thermal fluctuations which can promote phase mixing before the critical temperature is reached from above. In contrast with the cosmological quark-hadron transition, we find that the rapid cooling typical of the RHIC and LHC experiments and the fact that the quark-gluon plasma is chemically unsaturated suppress the role of non-perturbative effects at current collider energies. Significant supercooling is possible in a (nearly) homogeneous state of quark gluon plasma.
Using a Boltzmann equation, we investigate the nonequilibrium dynamics of nonperturbative fluctuations within the context of Ginzburg-Landau models. As an illustration, we examine how a two-phase system initially prepared in a homogeneous, low-temperature phase becomes populated by precursors of the opposite phase as the temperature is increased. We compute the critical value of the order parameter for the onset of percolation, which signals the breakdown of the conventional dilute gas approximation.
We study weakly first order cosmological phase transitions in finite temperature field theories. Focusing on the standard electroweak theory and its minimal supersymmetric extension, we identify the regimes of Higgs masses for which the phase transition in these models proceeds by significant phase mixing and the coarsening of the subsequent domain network. This dynamics is distinct from that for strongly first order transitions, which proceed by the nucleation and propagation of critical bubbles. We describe how electroweak baryogenesis might take place in these models, explaining how our new picture can relax the sphaleron washout bound of traditional scenarios.
We investigate nonequilibrium behavior in (1+1)-dimensional stochastic field theories in the context of Ginzburg-Landau models at varying cooling rates. We argue that a reliable measure of the departure from thermal equilibrium can be obtained from the absolute value of the rate of change of the momentum-integrated structure function, $ΔS_{\rm{tot}}$. We show that the peak of $ΔS_{\rm{tot}}$ scales with the cooling, or quench, time-scale, $τ_q$, in agreement with the prediction by Laguna and Zurek for the scaling of freeze-out time in both over and under-damped regimes. Furthermore, we show that the amplitude of the peak scales as $τ_q^{-6/5}$ independent of the viscosity.
We study the effects of anisotropic pressure on the properties of spherically symmetric, gravitationally bound objects. We consider the full general relativistic treatment of this problem and obtain exact solutions for various form of equations of state connecting the radial and tangential pressures. It is shown that pressure anisotropy can have significant effects on the structure and properties of stellar objects. In particular, the maximum value of 2M/R can approach unity (2M/R < 8/9 for isotropic objects) and the surface redshift can be arbitrarily large.
The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles are created due to thermal fluctuations, and can introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For reasonable choices of surface tension and correlation length, as obtained from the lattice QCD calculations, we show that the amount of phase mixing at the critical temperature remains below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP), within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogeneity of the medium results in a substantial reduction of the nucleation barrier for critical bubbles. Using the corrected nucleation barrier, we estimate the amount of supercooling for different parameters controlling the phase transition, and briefly discuss its implications to cosmology and heavy-ion collisions.
We show how to achieve lattice-spacing independent results in numerical simulations of finite-temperature stochastic scalar field theories. We generalize the previous approach of hep-lat/9607026 by obtaining results which are independent of the renormalization scale. As an application of our method, we examine thermal phase mixing in the context of Ginzburg-Landau models with short-range interactions. In particular, we obtain the lattice-spacing and renormalization-scale independent critical value of the control parameter which determines the free-energy barrier between the two low-temperature phases. We also propose a simple procedure to extract the critical value of control parameters for different choices of lattice spacing.
Long-lived localized field configurations such as breathers, oscillons, or more complex objects naturally arise in the context of a wide range of nonlinear models in different numbers of spatial dimensions. We present a numerical method, which we call the {\it adiabatic damping method}, designed to study such configurations in small lattices. Using 3-dimensional oscillons in $ϕ^4$ models as an example, we show that the method accurately (to a part in 10^5 or better) reproduces results obtained with static or dynamically expanding lattices, dramatically cutting down in integration time. We further present new results for 2-dimensional oscillons, whose lifetimes would be prohibitively long to study with conventional methods.
A quantum field theory warm inflation model is presented that solves the horizon/flatness problems. The model obtains, from the elementary dynamics of particle physics, cosmological scale factor trajectories that begin in a radiation dominated regime, enter an inflationary regime and then smoothly exit back into a radiation dominated regime, with nonnegligible radiation throughout the evolution.
The breaking of an approximate discrete symmetry, the final stages of a first order phase transition, or a post-inflationary biased probability distribution for scalar fields are possible cosmological scenarios characterized by the presence of unstable domain wall networks. Combining analytical and numerical techniques, we show that the non-spherical collapse of these domains can be a powerful source of gravitational waves. We compute their contribution to the stochastic background of gravitational radiation and explore their observability by present and future gravitational wave detectors.
We study under which conditions an overdamped regime can be attained in the dynamic evolution of a quantum field configuration. Using a real-time formulation of finite temperature field theory, we compute the effective evolution equation of a scalar field configuration, quadratically interacting with a given set of other scalar fields. We then show that, in the overdamped regime, the dissipative kernel in the field equation of motion is closely related to the shear viscosity coefficient, as computed in scalar field theory at finite temperature. The effective dynamics is equivalent to a time-dependent Ginzburg-Landau description of the approach to equilibrium in phenomenological theories of phase transitions. Applications of our results, including a recently proposed inflationary scenario called ``warm inflation'', are discussed.
During the past two decades, cosmologists turned to particle physics in order to explore the physics of the very early Universe. The main link between the physics of the smallest and largest structures in the Universe is the idea of spontaneous symmetry breaking, familiar from condensed matter physics. Implementing this mechanism into cosmology leads to the interesting possibility that phase transitions related to the breaking of symmetries in high energy particle physics took place during the early history of the Universe. These cosmological phase transitions may help us understand many of the challenges faced by the standard hot Big Bang model of cosmology, while offering a unique window into the very early Universe and the physics of high energy particle interactions.
We investigate the matching between (1+1)-dimensional nonlinear field theories coupled to an external stochastic environment and their lattice simulations. In particular, we focus on how to obtain numerical results which are lattice-spacing independent, and on how to extract the correct effective potential which emerges from the simulations. As an application, we study the thermal production of kink-antikink pairs, obtaining a number density of pairs which is lattice-spacing independent and the effective barrier for pair production, i.e., the effective kink mass.
The dynamics of phase transitions plays a crucial rôle in the so-called interface between high energy particle physics and cosmology. Many of the interesting results generated during the last fifteen years or so rely on simplified assumptions concerning the complex mechanisms typical of nonequilibrium field theories. After reviewing well-known results concerning the dynamics of first and second order phase transitions, I argue that much is yet to be understood, in particular in situations where homogeneous nucleation theory does not apply. I present a method to deal with departures from homogeneous nucleation, and compare its efficacy with numerical simulations. Finally, I discuss the interesting problem of matching numerical simulations of stochastic field theories with continuum models.
The study of nonlinear phenomena in systems with many degrees of freedom often relies on complex numerical simulations. In trying to model realistic situations, these systems may be coupled to an external environment which drives their dynamics. For nonlinear field theories coupled to thermal (or quantum) baths, discrete lattice formulations must be dealt with extreme care if the results of the simulations are to be interpreted in the continuum limit. Using techniques from renormalization theory, a self-consistent method is presented to match lattice results to continuum models. As an application, symmetry restoration in $ϕ^4$ models is investigated.
I briefly review the main ideas and challenges involved in the computation of the observed baryonic asymmetry of the Universe.
In models of real scalar fields with degenerate double-well potentials, spherically symmetric, large amplitude fluctuations away from the vacuum are unstable. Neglecting interactions with an external environment, the evolution of such configurations may entail the development of an oscillon; a localized, non-singular, time-dependent configuration which is {\it extremely} long-lived. In the present study we investigate numerically how the coupling to a heat bath influences the evolution of collapsing bubbles. We show that the existence and lifetime of the oscillon stage is extremely sensitive to how strongly the field is coupled to the heat bath. By modeling the coupling through a Markovian Langevin equation with viscosity coefficient $γ$, we find that for $γ\gtrsim 5 \times 10^{-4}m$, where $m$ is the typical mass scale in the model, oscillons are not observed.