Search

We introduce a new approach for cosmological parameter estimation based on the information-theoretical Jensen-Shannon divergence (${\cal D}_{\rm JS}$), calculating it for models in the restricted parameter space $\{H_0, w_0, w_a\}$, where $H_0$ is the value of the Hubble constant today, and $w_0$ and $w_a$ are dark energy parameters, with the other parameters held fixed at their best-fit values from the Planck 2018 data. As an application, we investigate the $H_0$ tension between the Planck temperature power spectrum data (TT) and the local astronomical data by comparing the $\Lambda$CDM model with the $w$CDM and the $w_0w_a$CDM dynamic dark energy models. We find agreement with other works using the standard Bayesian inference for parameter estimation; in addition, we show that while the ${\cal D}_{\rm JS}$ is equally minimized for both values of $H_0$ along the $(w_0,w_a)$ plane, the lines of degeneracy are different for each value of $H_0$. This allows for distinguishing between the two, once the value of either $w_0$ or $w_a$ is known., Comment: 5 pages, 3 figures. Final version accepted for publication in Physical Review D. Includes a new error analysis, a new figure, additional references, and a new author

Oscillons are long-lived, spherically symmetric, attractor scalar field configurations that emerge as certain field configurations evolve in time. It has been known for many years that there is a direct correlation between the initial configuration’s shape and the resulting oscillon lifetime: a shape memory. In this paper, we use an information-entropic measure of spatial complexity known as differential configurational entropy (DCE) to obtain estimates of oscillon lifetimes in scalar field theories with symmetric and asymmetric double-well potentials. The time-dependent DCE is built from the Fourier transform of the two-point correlation function of the energy density of the scalar field configuration. We obtain a scaling law correlating oscillon lifetimes and measures obtained from its evolving DCE. For the symmetric double well, for example, we show that we can apply DCE to predict an oscillon’s lifetime with an average accuracy of 6% or better. We also show that the DCE acts as a pattern discriminator, able to distinguish initial configurations that evolve into long-lived oscillons from other nonperturbative short-lived fluctuations.

We investigate the rich nonlinear dynamics during the end of hilltop inflation by numerically solving the coupled Klein-Gordon-Friedmann equations in a expanding universe. In particular, we search for coherent, nonperturbative configurations that may emerge due to the combination of nontrivial couplings between the fields and resonant effects from the cosmological expansion. We couple a massless field to the inflaton to investigate its effect on the existence and stability of coherent configurations and the effective equation of state at reheating. For parameters consistent with data from the Planck and WMAP satellites, and for a wide range of couplings between the inflaton and the massless field, we identify a transition from disorder to order characterized by emergent oscillon-like configurations. We verify that these configurations can contribute a maximum of roughly 30% of the energy density in the universe. At late times their contribution to the energy density drops to about 3%, but they remain long-lived on cosmological time-scales, being stable throughout our simulations. Cosmological oscillon emergence is described using a new measure of order in field theory known as relative configurational entropy., 10 pages, 6 figures totaling 25 .eps files

Oscillons are localized, non-singular, time-dependent, spherically-symmetric solutions of nonlinear scalar field theories which, although unstable, are extremely long-lived. We show that they naturally appear during the collapse of subcritical bubbles in models with symmetric and asymmetric double-well potentials. By a combination of analytical and numerical work we explain several of their properties, including the conditions for their existence, their longevity, and their final demise. We discuss several contexts in which we expect oscillons to be relevant. In particular, their nucleation during cosmological phase transitions may have wide-ranging consequences., Comment: 31 pages Revtex, 20 uufiles-encoded figures. Section "Possible Applications of Oscillons" slightly expanded

We propose a measure of order in the context of nonequilibrium field theory and argue that this measure, which we call relative configurational entropy (RCE), may be used to quantify the emergence of coherent low-entropy configurations, such as time-dependent or time-independent topological and nontopological spatially-extended structures. As an illustration, we investigate the nonequilibrium dynamics of spontaneous symmetry-breaking in three spatial dimensions. In particular, we focus on a model where a real scalar field, prepared initially in a symmetric thermal state, is quenched to a broken-symmetric state. For a certain range of initial temperatures, spatially-localized, long-lived structures known as oscillons emerge in synchrony and remain until the field reaches equilibrium again. We show that the RCE correlates with the number-density of oscillons, thus offering a quantitative measure of the emergence of nonperturbative spatiotemporal patterns that can be generalized to a variety of physical systems., LaTeX, 9 pages, 5 figures, 1 table

We examine the nonequilibrium dynamics of a self-interacting $\lambda\phi^4$ scalar field theory. Using a real time formulation of finite temperature field theory we derive, up to two loops and $O(\lambda^2)$, the effective equation of motion describing the approach to equilibrium. We present a detailed analysis of the approximations used in order to obtain a Langevin-like equation of motion, in which the noise and dissipation terms associated with quantum fluctuations obey a fluctuation-dissipation relation. We show that, in general, the noise is colored (time-dependent) and multiplicative (couples nonlinearly to the field), even though it is still Gaussian distributed. The noise becomes white in the infinite temperature limit. We also address the effect of couplings to other fields, which we assume play the r\^ole of the thermal bath, in the effective equation of motion for $\phi$. In particular, we obtain the fluctuation and noise terms due to a quadratic coupling to another scalar field., Comment: 30 pages, LaTex (uses RevTex 3.0), DART-HEP-93/06

The evolution of spherically symmetric unstable scalar field configurations (``bubbles'') is examined for both symmetric (SDWP) and asymmetric (ADWP) double-well potentials. Bubbles with initial static energies $E_0\la E_{{\rm crit}}$, where $E_{{\rm crit}}$ is some critical value, shrink in a time scale determined by their linear dimension, or ``radius''. Bubbles with $E_0\ga E_{{\rm crit}}$ evolve into time-dependent, localized configurations which are {\it very} long-lived compared to characteristic time-scales in the models examined. The stability of these configurations is investigated and possible applications are briefly discussed.tic time-scales in the models examined. The stability of these configurations is investigated and possible applications are briefly discussed., Comment: 10 pages, LaTeX (uses revtex 3.0), 4 figures (postscript files of figs.1 and 2 appended starting on line 497), report DART-HEP-93/05

We investigate the nonlinear dynamics of hybrid inflation models, which are characterized by two real scalar fields interacting quadratically. We start by solving numerically the coupled Klein-Gordon equations in static Minkowski spacetime, searching for possible coherent structures. We find long-lived, localized configurations, which we identify as a new kind of oscillon. We demonstrate that these two-field oscillons allow for "excited" states with much longer lifetimes than those found in previous studies of single-field oscillons. We then solve the coupled field equations in an expanding Friedmann-Robertson-Walker spacetime, finding that as the field responsible for inflating the Universe rolls down to oscillate about its minimum, it triggers the formation of long-lived two-field oscillons, which can contribute up to 20% of the total energy density of the Universe. We show that these oscillons emerge for a wide range of parameters consistent with WMAP 7-year data. These objects contain total energy of about 25*10^20 GeV, localized in a region of approximate radius 6*10^-26 cm. We argue that these structures could have played a key role during the reheating of the Universe., Comment: 12 pages, 10 .pdf figures, uses RevTex4; v2: expanded discussion in section IV, accepted for publication in Phys.Rev. D. Results remain the same

We examine the computation of the nucleation barrier used in the expression for false vacuum decay rates in finite-temperature field theory. By a detailed analysis of the determinantal prefactor, we show that the correct bounce solution used in the computation of the nucleation barrier should not include loop corrections coming from the scalar field undergoing decay. Temperature corrections to the bounce appear from loop contributions from other fields coupled to the scalar field. We compute the nucleation barrier for a model of scalar fields coupled to fermions, and compare our results to the expression commonly used in the literature. We find that, for large enough self-couplings, the inclusion of scalar loops in the expression of the nucleation barrier leads to an underestimate of the decay rate in the neighborhood of the critical temperature.

We study analytically and numerically the decay of a metastable phase in (1+1)-dimensional classical field theory coupled to a heat bath. By a numerical simulation we obtain the nucleation barrier as a function of the energy difference between the metastable and stable phases, and compare it to the theoretical prediction from the critical bubble calculation. The numerical results provide strong confirmation of the theory.

Through a detailed numerical investigation in three spatial dimensions, we demonstrate that long-lived time-dependent field configurations emerge dynamically during symmetry breaking in an expanding de Sitter spacetime. We investigate two situations: a single scalar field with a double-well potential and the bosonic sector of an SU(2) non-Abelian Higgs model. For the single scalar, we show that large-amplitude oscillon configurations emerge spontaneously and persist to contribute about 1.2% of the energy density of the universe. We also show that for a range of parameters, oscillon lifetimes are enhanced by the expansion and that this effect is a result of parametric resonance. For the SU(2) case, we see about 4% of the final energy density in oscillons., Comment: 10 pages, RevTex4, 6 figures; v2: expanded SU(2) model section, added 2 figures, added one section, improved overall presentation and updated references, accepted for publication in Phys. Rev. D. Results remain the same

We present a comprehensive, nonperturbative analytical method to investigate the dynamics of time-dependent oscillating scalar field configurations. The method is applied to oscillons in a double well Klein-Gordon model in two and three spatial dimensions, yielding high accuracy results in the characterization of all aspects of the complex oscillon dynamics. In particular, we show how oscillons can be interpreted as long-lived perturbations about an attractor in field configuration space. By investigating their radiation rate as they approach the attractor, we obtain an accurate estimate of their lifetimes in d=3 and explain why they seem to be perturbatively stable in d=2, where d is the number of spatial dimensions., Comment: 15 pages, 17 figures, RevTex

The possibility, often explored in the literature, that field theories exhibit metastable vacuum states in the background of a hot expanding universe is examined. By studying the finite-temperature effective potential for self-interacting scalar fields and also for scalar fields interacting with fermion fields, the conditions for the existence of a metastable vacuum are derived. The effects of asymmetries on the effective potential as well as of couplings of the scalar field to other fields on the kinetics of the phase transition are examined. Possible applications to electroweak symmetry breaking, the quark-hadron phase transition, and the primordial formation of nontopological solitons are briefly discussed.

The possibility that extremely long-lived, time-dependent, and localized field configurations (``oscillons'') arise during the collapse of asymmetrical bubbles in (2+1)-dimensional ${\ensuremath{\varphi}}^{4}$ models is investigated. It is found that oscillons can develop from a large spectrum of elliptically deformed bubbles. Moreover, we provide numerical evidence that such oscillons are (a) circularly symmetric and (b) linearly stable against small arbitrary radial and angular perturbations. The latter is based on a dynamical approach designed to investigate the stability of nonintegrable time-dependent configurations that is capable of probing slowly growing instabilities not seen through the usual ``spectral'' method.

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., Comment: 45 pages, 5 figures, Latex, In press Phys. Rev. D, minor corrections

We present a cosmological analysis of a six-dimensional Einstein-Yang-Mills-Higgs model with SO(3) invariance to which is added a matter term. An analytical expression for the time variation of the internal radius is obtained together with the predictions for the variations of the coupling ''constants'' involved. Their variation is limited to the very early stages of the cosmological evolution since the internal radius quickly becomes constant. It is shown that, once the asymptotic behavior sets in, the four-dimensional space-time expands linearly in time with a zero effective cosmological constant, after fine tuning.

We study possible cosmological solutions to N = 1, D = 10 supergravity with the Yang-Mills field strength set to zero and show that the model accepts both power-law solutions and exponential solutions in the large-time limit. The stability of these solutions is investigated. It is found that a shrinking internal space is compatible with several field configurations. Using a stable power-law solution we analyze the conditions to obtain enough inflation in the physical space from the shrinking internal dimensions. We also show that for a flat topology a de Sitter phase is possible for late times. We used the consistency with the density perturbations to fix the inflationary parameter.