We derive the nonequilibrium real-time evolution of an $O(N)$-invariant scalar quantum field theory in presence a nonvanishing expectation value field. Using systematic $1/N$ expansion 2PI effective action to next-to-leading order, we obtain nonperturbative equations which include scattering and memory effects. The equivalence direct method, requires resummation infinite number skeleton diagrams, with auxiliary-field formalism, involves only one diagram at is shown.

We propose a new one-parameter family of Landau gauges for Yang-Mills theories which can be formulated by means functional integral methods and are thus well suited analytic calculations, but free Gribov ambiguities avoid the Neuberger zero problem standard Faddeev-Popov construction. The resulting gauge-fixed theory is perturbatively renormalizable in four dimensions and, what concerns calculation ghost gauge field correlators, it reduces to massive extension action. study renormalization...

We present the first study of parametric resonance in quantum field theory from a complete next-to-leading order calculation 1/N-expansion 2PI effective action, which includes scattering and memory effects. numerical solution for an O(N)-symmetric scalar provide approximate analytic description nonlinear dynamics entire amplification range. find that classical resonant at early times is followed by collective regime with explosive particle production broad momentum range, not accessible...

We study the quantum theory of an $O(N)$ scalar field on de Sitter geometry at leading order in a nonperturbative $1/N$ expansion. This resums infinite series so-called superdaisy loop diagrams. obtain symmetric solutions corresponding, properly renormalized, dynamical equations and compute complete effective potential. Because its self-interactions, acquires strictly positive square mass which screens potential infrared divergences. Moreover, strongly enhanced ultralong-wavelength...

We study the $O(N)$ scalar field theory with quartic self-coupling in de Sitter space. When is light units of expansion rate, perturbative methods break down at very low momenta due to large infrared logarithmic terms. Using nonperturbative large-$N$ limit, we compute four-point vertex function deep regime. The resummation an infinite series (bubble) diagrams leads a modified power law which analogous generation anomalous dimension critical phenomena. discuss detail role high momentum...

We consider a simple massive extension of the Landau-DeWitt gauge for SU($N$) Yang-Mills theory. compute corresponding one-loop effective potential temporal background gluon field at finite temperature. At this order is simply related to Polyakov loop, parameter deconfinement transition. Our perturbative calculation correctly describes quark confining phase low temperature and transition second $N=2$ weakly first $N=3$. estimates temperatures are in qualitative agreement with values from...

We derive the most general evolution equations describing in-medium (anti)neutrino propagation in mean-field approximation. In particular, we consider various types of neutrino-antineutrino mixing, for both Dirac and Majorana fields, resulting either from nontrivial pair correlations or helicity coherence due to nonvanishing neutrino masses. show that, unless medium is spatially homogeneous isotropic, these are sourced by usual antineutrino densities. This may be importance astrophysical...

We study the dynamics of light quantum scalar fields in de Sitter space on superhorizon scales. compute self-energy an $O(N)$ symmetric theory at next-to-leading order a $1/N$ expansion regime momenta, and we obtain exact analytical solution corresponding Dyson-Schwinger equations for two-point correlator. This amounts to resumming infinite series nonlocal insertions, which typically generate spurious infrared and/or secular divergences. The potentially large logarithms resum into...

We investigate scalar field theories in de Sitter space by means of nonperturbative renormalization group techniques. compute the functional flow equation for effective potential O(N) local approximation and we study onset curvature-induced effects as quantum fluctuations are progressively integrated out from subhorizon to superhorizon scales. This results a dimensional reduction original action an zero-dimensional Euclidean theory. show that latter is equivalent both late-time equilibrium...

We compute the renormalization group flow of O(N) scalar field theories in de Sitter space using nonperturbative techniques local potential approximation. obtain effective on superhorizon scales for arbitrary space-time dimension D=d+1. show that, due to strong infrared fluctuations, latter is qualitatively similar corresponding one Euclidean with D=0. It follows that spontaneously broken symmetries are radiatively restored any and value N.

We study the Landau gauge correlators of Yang-Mills fields for infrared Euclidean momenta in context a massive extension Faddeev-Popov Lagrangian which, we argue, underlies variety continuum approaches. Standard (perturbative) renormalization group techniques with specific, infrared-safe scheme produce so-called decoupling and scaling solutions ghost gluon propagators, which correspond to nontrivial fixed points. The point is stable weakly coupled, while unstable generically strongly coupled...

We study the confinement-deconfinement phase transition of pure Yang-Mills theories at finite temperature using a simple massive extension standard background field methods. generalize our recent next-to-leading-order perturbative calculation Polyakov loop and related effective potential for SU(2) theory to any compact connex Lie group with algebra. discuss in detail SU(3) theory, where two-loop corrections yield improved values first-order as compared one-loop result. also show that certain...

In a recent work we have proposed perturbative approach for the study of phase transition pure Yang-Mills theories at finite temperature. This is based on simple massive extension background field methods in Landau-DeWitt gauge, where gluon mass term related to existence Gribov ambiguities. We shown that one-loop calculation effective potential describes well structure SU(2) and SU(3) theories. Here, present next-to-leading-order contribution perturbation theory case. particular, compute...

We investigate the phase diagram of QCD with heavy quarks at finite temperature and chemical potential in context background field methods. In particular, we use a massive extension Landau-DeWitt gauge which is motivated by previous studies deconfinement transition pure Yang-Mills theories. show that simple one-loop calculation able to capture richness quark region, both real imaginary potential. Moreover, dimensionless ratios quantities directly measurable numerical simulations are good...

We study the backreaction of superhorizon fluctuations a light quantum scalar field on classical de Sitter geometry by means Wilsonian renormalization group. This allows us to treat gravitationally amplified in nonperturbative manner and analytically follow induced flow spacetime curvature as long wavelength modes are progressively integrated out. Unbounded loop corrections deep infrared eventually screened effects which stabilize geometry.

High-temperature resummed perturbation theory is plagued by poor convergence properties. The problem appears for theories with bosonic field content such as QCD, QED or scalar theories. We calculate the pressure well other thermodynamic quantities at high temperature a one-component theory, solving three-loop 2PI effective action numerically without further approximations. present detailed comparison two-loop approximation. One observes strongly improved behavior compared to perturbative...

We study the real-time evolution of a self-interacting $O(N)$ scalar field initially prepared in pure, coherent quantum state. present complete solution nonequilibrium dynamics from $1/N$ expansion two-particle-irreducible effective action at next-to-leading order, which includes scattering and memory effects. demonstrate that, restricting one's attention (or ability to measure) subset infinite hierarchy correlation functions, one observes an loss purity or coherence and, on longer time...

We consider the two-point correlators of Yang-Mills theories at finite temperature in Landau gauge. employ a model for corresponding based on inclusion an effective mass term gluons. The latter is expected to have its origin existence Gribov copies. One-loop calculations zero been shown agree remarkably well with lattice data. extend this and perform one-loop calculation Matsubara gluon ghost temperature. show that, as vacuum, accurately captures dominant infrared physics magnetic...

We propose a one-parameter family of nonlinear covariant gauges which can be formulated as an extremization procedure that may amenable to lattice implementation. At high energies, where the Gribov ambiguities ignored, this reduces Curci-Ferrari-Delbourgo-Jarvis gauges. further continuum formulation in terms local action is free and avoids Neuberger zero problem standard Faddeev-Popov construction. This involves averaging over copies with nonuniform weight, introduces new gauge-fixing...

Nonperturbative renormalization group techniques have recently proven a powerful tool to tackle the nontrivial infrared dynamics of light scalar fields in de Sitter space. In present article, we develop formalism beyond local potential approximation employed earlier works. particular, consider derivative expansion, systematic expansion powers field derivatives, appropriate for long wavelength modes, that generalize relevant case curved metric with Lorentzian signature. The method is...

We extend a previous investigation [U. Reinosa et al., Phys. Rev. D 92, 025021 (2015)] of the QCD phase diagram with heavy quarks in context background field methods by including two-loop corrections to effective potential. The nonperturbative dynamics pure-gauge sector is modeled phenomenological gluon mass term Landau-DeWitt gauge-fixed action, which results an improved perturbative expansion. investigate at nonzero temperature and (real or imaginary) chemical Two-loop yield agreement...