Field theoretical methods in cosmology (original) (raw)
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Dissipation via particle production in scalar field theories
Physical Review D, 1995
Hartree approximation and clearly exhibit dissipative effects related to the thresholds to particle production. The asymptotic dynamics depends on the coupling and initial conditions but does not seem to lead to exponential relaxation. The effect of dissipation by Goldstone bosons is studied non-perturbatively in the large N limit in an O(N) theory. Dissipation produced by Goldstone bosons dramatically changes the picture of the phase transition. We find the remarkable result that for ``slow-roll'' initial conditions (with the expectation value of the field initially near the origin) the final value of the expectation value of the scalar field is very close to its initial value. We find that the minima of the effective action depend on the initial conditions. We provide extensive numerical analysis of the dynamics.
Asymptotic dynamics in scalar field theory: Anomalous relaxation
Physical Review D, 1998
We analyze the dynamics of dissipation and relaxation in the unbroken and broken symmetry phases of scalar theory in the nonlinear regime for large initial energy densities, and after linear unstabilities (parametric or spinodal) are shut-off by the quantum backreaction. A new time scale emerges that separates the linear from the non-linear regimes. This scale is non- perturbative in the coupling and initial amplitude. The non-perturbative evolution is studied in the large the N limit for the O(N) vector model. A combination of numerical analysis and the multitime scale analysis reveals the presence of unstable bands in the nonlinear regime. These are associated with power law growth of quantum fluctuations, that result in power law relaxation and dissipation with non-universal and non-perturbative dynamical anomalous exponents.We find substantial particle production during this non-linear evolu- tion which is of the same order as that in the linear regime. The expectation value of the scalar field vanishes asymptotically transferring all of the initial energy into produced particles via the non-linear resonances in the unbroken symmetry phase.The effective mass for the quantum modes tends asympto- tically to a constant plus oscillating O(1/t) terms. This slow decay causes the power behaviour in the modes which become free for t=infty. We derive a simple expression for the equation of state for the fluid of produced particles that interpolates between radiation-type and dust-type equations according to the initial value of the order parameter for unbroken symmetry. For broken symmetry the produced particles are massless Goldstone bosons with a radiation-type equation of state. We find the onset of a novel form of dynamical Bose condensation in the collisionless regime in the absence of thermalization.
2005
We study the symmetry breaking pattern of an O(4) symmetric model of scalar fields, with both charged and neutral fields, interacting with a photon bath. Nagasawa and Brandenberger argued that in favourable circumstances the vacuum manifold would be reduced from S^3 to S^1. Here it is shown that a selective condensation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal ``external'' dissipation, i.e. not related to interactions with a bath. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion.
Nonequilibrium dynamics in quantum field theory at high density: The “tsunami”
Physical Review D, 2001
The dynamics of a dense relativistic quantum fluid out of thermodynamic equilibrium is studied in the framework of the ⌽ 4 scalar field theory in the large N limit. The time evolution of a particle distribution in momentum space ͑the tsunami͒ is computed. The effective mass felt by the particles in such a high density medium equals the tree level mass plus the expectation value of the squared field. The case of negative tree level squared mass is particularly interesting. In such a case dynamical symmetry restoration as well as dynamical symmetry breaking can happen. Furthermore, the symmetry may stay broken with a vanishing asymptotic squared mass showing the presence of out of equilibrium Goldstone bosons. We study these phenomena and identify the set of initial conditions that lead to each case. We compute the equation of state which turns out to depend on the initial state. Although the system does not thermalize, the equation of state for asymptotically broken symmetry is of radiation type. We compute the correlation functions at equal times. The two point correlator for late times is the sum of different terms. One stems from the initial particle distribution. Another term accounts for the out of equilibrium Goldstone bosons created by spinodal unstabilities when the symmetry is asymptotically broken. Both terms are of the order of the inverse of the coupling for distances where causal signals can connect the two points. The contribution of the out of equilibrium Goldstones exhibits scaling behavior in a generalized sense.
Role of dissipation in biasing the vacuum selection in quantum field theory at finite temperature
Physical Review D, 2005
We study the symmetry breaking pattern of an O(4) symmetric model of scalar fields, with both charged and neutral fields, interacting with a photon bath. Nagasawa and Brandenberger argued that in favourable circumstances the vacuum manifold would be reduced from S 3 to S 1. Here it is shown that a selective condensation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal "external" dissipation, i.e. not related to interactions with a bath. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion.
Resonant particle production with nonminimally coupled scalar fields in preheating after inflation
Physical Review D, 1999
We investigate a resonant particle production of a scalar field χ coupled non-minimally to a spacetime curvature R (ξRχ 2 ) as well as to an inflaton field φ (g 2 φ 2 χ 2 ). In the case of g < ∼ 3 × 10 −4 , ξ effect assists g-resonance in certain parameter regimes. However, for g > ∼ 3 × 10 −4 , g-resonance is not enhanced by ξ effect because of ξ suppression effect as well as a back reaction effect. If ξ ≈ −4, the maximal fluctuation of produced χ-particle is χ 2 max ≈ 2 × 10 17 GeV for g < ∼ 1 × 10 −5 , which is larger than the minimally coupled case with g ≈ 1 × 10 −3 . 98.80.Cq, 05.70.Fh, 11.15.Kc * electronic address:shinji@gravity.phys.waseda.ac.jp † electronic address:maeda@gravity.phys.waseda.ac.jp ‡ electronic address:torii@th.phys.titech.ac.jp ticles [ . This initial evolutionary phase, which is called preheating stage, provides an explosive particle production and must be discussed separately from the perturbative decay of inflaton. There are many works about the preheating stage based on analytical investigations as well as on numerical studies . The important feature with the existence of preheating stage is that the maximal value of produced fluctuation can be so large that it would result in a non-thermal phase transition and make baryogenesis at the GUT scale possible , although the baryogenesis might be important in much lower energy scale, i.e. the electro-weak scale .
Physics at the Interface of Particle Physics and Cosmology
Eprint Arxiv Hep Ph 9808418, 1998
In these lectures I examine some of the principal issues in cosmology from a particle physics point of view. I begin with nucleosynthesis and show how the primordial abundance of the light elements can help fix the number of (light) neutrino species and determine the ratio eta\etaeta of baryons to photon in the universe now. The value of eta\etaeta obtained highlights two of the big open problems of cosmology: the presence of dark matter and the need for baryogenesis. After discussing the distinction between hot and cold dark matter, I examine the constraints on, and prospect for, neutrinos as hot dark matter candidates. I show next that supersymmetry provides a variety of possibilities for dark matter, with neutralinos being excellent candidates for cold dark matter and gravitinos, in some scenarios, possibly providing some form of warm dark matter. After discussing axions as another cold dark matter candidate, I provide some perspectives on the nature of dark matter before turning to baryogenesis. Here I begin by outlining the Sakharov conditions for baryogenesis before examining the issues and challenges of producing a, large enough, baryon asymmetry at the GUT scale. I end my lectures by discussing the Kuzmin-Rubakov-Shaposhnikov mechanism and issues associated with electrical baryogenesis. In particular, I emphasize the implications that generating the baryon asymmetry at the electroweak scale has for present-day particle physics.
Dissipation, Noise, and Vacuum Decay in Quantum Field Theory
Physical Review Letters, 2001
We study the process of vacuum decay in quantum field theory focusing on the stochastic aspects of the interaction between long and short-wavelength modes. This interaction results in a diffusive behavior of the reduced Wigner function describing the state of the long-wavelength modes, and thereby to a finite activation rate even at zero temperature. This effect can make a substantial contribution to the total decay rate.