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Marcelo Gleiser

Publications and source records attributed to Marcelo Gleiser.

At least 55 records · Page 3Linked to original sources
arXiv2007

Dynamical Emergence of Complex Structures in Field Theories

Nonlinear field theories can be used to study both standard physics questions, or to study questions such as the emergence of order and complexity. These theories are generally derived from the symmetries of a given problem and the interactions that respect those symmetries. Formally one can then quantize the system to find the masses of the fundamental excitations, but this procedure generally destroys much information about solutions of the field equations with large non-perturbative amplitudes. To get information about the properties of the solutions to these field theories without perturbative approximations we use real time lattice simulations where complex spatiotemporal structures emerge dynamically from excess free energy and a thermal background. We present results in 2 and 3 dimensions of new interacting quasi-particle formations from a quench. These objects show an emergent level of complexity which we attempt to categorize and define in a manner that should be useful to many different applications.

nlin.AO↗
arXiv2007

Bubbling the False Vacuum Away

We investigate the role of nonperturbative, bubble-like inhomogeneities on the decay rate of false-vacuum states in two and three-dimensional scalar field theories. The inhomogeneities are induced by setting up large-amplitude oscillations of the field about the false vacuum as, for example, after a rapid quench or in certain models of cosmological inflation. We show that, for a wide range of parameters, the presence of large-amplitude bubble-like inhomogeneities greatly accelerates the decay rate, changing it from the well-known exponential suppression of homogeneous nucleation to a power-law suppression. It is argued that this fast, power-law vacuum decay -- known as resonant nucleation -- is promoted by the presence of long-lived oscillons among the nonperturbative fluctuations about the false vacuum. A phase diagram is obtained distinguishing three possible mechanisms for vacuum decay: homogeneous nucleation, resonant nucleation, and cross-over. Possible applications are briefly discussed.

hep-th↗
arXiv2007

A Phase Transition in U(1) Configuration Space: Oscillons as Remnants of Vortex-Antivortex Annihilation

We show that the low-momentum scattering of vortex-antivortex pairs can lead to very long-lived oscillon states in 2d Abelian Higgs models. The emergence of oscillons is controlled by the ratio of scalar and vector field masses, $β=(m_s/m_v)^2$ and can be described as a phase transition in field configuration space with critical value $β_c\simeq 0.13(6)\pm 2 $: only models with $β<β_c$ lead to oscillon-like remnants. The critical behavior of the system obeys a power law $O(β)\sim |β-β_c|^o$, where $O$ is an order parameter indicating the presence of oscillons and $o = 0.2(2)\pm 2 $ is the critical exponent.

hep-th↗
arXiv2006

Asymmetric Spatiotemporal Evolution of Prebiotic Homochirality

The role of asymmetry on the evolution of prebiotic homochirality is investigated in the context of autocatalytic polymerization reaction networks. A model featuring enantiometric cross-inhibition and chiral bias is used to study the diffusion equations controlling the spatiotemporal development of left and right-handed domains. Bounds on the chiral bias are obtained consistent with present-day constraints on the emergence of life on early Earth. The viability of biasing mechanisms such as weak neutral currents and circularly polarized UV light is discussed. The results can be applied to any hypothetical planetary platform.

astro-ph↗
arXiv2006

Emergence of Complex Spatio-Temporal Behavior in Nonlinear Field Theories

We investigate the emergence of time-dependent nonperturbative configurations during the evolution of nonlinear scalar field models with symmetric and asymmetric double-well potentials. Complex spatio-temporal behavior emerges as the system seeks to establish equipartition after a fast quench. We show that fast quenches may dramatically modify the decay rate of metastable states in first order phase transitions. We briefly suggest possible applications incondensed matter systems and early universe cosmology.

hep-ph↗
arXiv2006

Oscillons in Scalar Field Theories: Applications in Higher Dimensions and Inflation

The basic properties of oscillons -- localized, long-lived, time-dependent scalar field configurations -- are briefly reviewed, including recent results demonstrating how their existence depends on the dimensionality of spacetime. Their role on the dynamics of phase transitions is discussed, and it is shown that oscillons may greatly accelerate the decay of metastable vacuum states. This mechanism for vacuum decay -- resonant nucleation -- is then applied to cosmological inflation. A new inflationary model is proposed which terminates with fast bubble nucleation.

hep-th↗
arXiv2006

Energy Landscape of d-Dimensional Q-balls

We investigate the properties of $Q$-balls in $d$ spatial dimensions. First, a generalized virial relation for these objects is obtained. We then focus on potentials $V(ϕϕ^{\dagger})= \sum_{n=1}^{3} a_n(ϕϕ^{\dagger})^n$, where $a_n$ is a constant and $n$ is an integer, obtaining variational estimates for their energies for arbitrary charge $Q$. These analytical estimates are contrasted with numerical results and their accuracy evaluated. Based on the results, we offer a simple criterion to classify ``large'' and ``small'' $d$-dimensional $Q$-balls for this class of potentials. A minimum charge is then computed and its dependence on spatial dimensionality is shown to scale as $Q_{\rm min} \sim \exp(d)$. We also briefly investigate the existence of $Q$-clouds in $d$ dimensions.

hep-th↗
arXiv2006

Prebiotic Homochirality as a Critical Phenomenon

The development of prebiotic homochirality on early-Earth or another planetary platform may be viewed as a critical phenomenon. It is shown, in the context of spatio-temporal polymerization reaction networks, that environmental effects -- be them temperature surges or other external disruptions -- may destroy any net chirality previously produced. In order to understand the emergence of prebiotic homochirality it is important to model the coupling of polymerization reaction networks to different planetary environments.

astro-ph↗
arXiv2005

Resonant Nucleation

We investigate the role played by fast quenching on the decay of metastable (or false vacuum) states. Instead of the exponentially-slow decay rate per unit volume, $Γ_{\rm HN} \sim \exp[-E_b/k_BT]$ ($E_b$ is the free energy of the critical bubble), predicted by Homogeneous Nucleation theory, we show that under fast enough quenching the decay rate is a power law $Γ_{\rm RN} \sim [E_b/k_BT]^{-B}$, where $B$ is weakly sensitive to the temperature. For a range of parameters, large-amplitude oscillations about the metastable state trigger the resonant emergence of coherent subcritical configurations. Decay mechanisms for different $E_b$ are proposed and illustrated in a (2+1)-dimensional scalar field model.

hep-ph↗
arXiv2004

d-dimensional Oscillating Scalar Field Lumps and the Dimensionality of Space

Extremely long-lived, time-dependent, spatially-bound scalar field configurations are shown to exist in $d$ spatial dimensions for a wide class of polynomial interactions parameterized as $V(ϕ) = \sum_{n=1}^h\frac{g_n}{n!}ϕ^n$. Assuming spherical symmetry and if $V''<0$ for a range of values of $ϕ(t,r)$, such configurations exist if: i) spatial dimensionality is below an upper-critical dimension $d_c$; ii) their radii are above a certain value $R_{\rm min}$. Both $d_c$ and $R_{\rm min}$ are uniquely determined by $V(ϕ)$. For example, symmetric double-well potentials only sustain such configurations if $d\leq 6$ and $R^2\geq d[3(2^{3/2}/3)^d-2]^{-1/2}$. Asymmetries may modify the value of $d_c$. All main analytical results are confirmed numerically. Such objects may offer novel ways to probe the dimensionality of space.

hep-th↗
arXiv2004

Anisotropic Stars: Exact Solutions and Stability

I report on recent work concerning the existence and stability of self-gravitating spheres with anisotropic pressure. After presenting new exact solutions, Chandrasekhar's variational formalism for radial perturbations is generalized to anisotropic objects and applied to investigate their stability. It is shown that anisotropy can not only support stars of mass M and radius R with 2M/R > 8/9 and arbitrarily large surface redshifts, but that stable configurations exist for values of the adiabatic index smaller than the corresponding isotropic value.

astro-ph↗
arXiv2004

What We Know and What We Don't Know About the Universe

I present a non-technical and necessarily biased and incomplete overview of our present understanding of the physical universe and its constituents, emphasizing what we have learned from the explosive growth in cosmological and astrophysical data acquisition and some of the key open questions that remain. The topics are organized under the labels space, time, and matter. Most bibliographical references are for the non-expert.

astro-ph↗
arXiv2003

Resonant nucleation of spatio-temporal order via parametric modal amplification

We investigate, analytically and numerically, the emergence of spatio-temporal order in nonequilibrium scalar field theories. The onset of order is triggered by destabilizing interactions (DIs), which instantaneously change the interacting potential from a single to a double-well, tunable to be either degenerate (SDW) or nondegenerate (ADW). For the SDW case, we observe the emergence of spatio-temporal coherent structures known as oscillons. We show that this emergence is initially synchronized, the result of parametric amplification of the relevant oscillon modes. We also discuss how these ordered structures act as bottlenecks for equipartition. For ADW potentials, we show how the same parametric amplification mechanism may trigger the rapid decay of a metastable state. For a range of temperatures, the decay rates associated with this resonant nucleation can be orders of magnitude larger than those computed by homogeneous nucleation, with time-scales given by a simple power law, $τ_{\rm RN}\sim[E_b/k_BT]^B$, where $B$ depends weakly on the temperature and $E_b/k_BT$ is the free-energy barrier of a critical fluctuation.

cond-mat↗
arXiv2003

Resonant emergence of global and local spatiotemporal order in a nonlinear field model

We investigate the nonequilibrium evolution of a scalar field in (2+1) dimensions. The field is set in a double-well potential in contact (open) or not (closed) with a heat bath. For closed systems, we observe the synchronized emergence of coherent spatiotemporal configurations, identified with oscillons. This initial global ordering degenerates into localized order until all oscillons disappear. We show that the synchronization is driven by resonant parametric oscillations of the field's zero mode and that local ordering is only possible outside equipartition. None of these orderings occur for open systems.

hep-ph↗
arXiv2003

Anisotropic Stars II : Stability

We investigate the stability of self-gravitating spherically symmetric anisotropic spheres under radial perturbations. We consider both the Newtonian and the full general-relativistic perturbation treatment. In the general-relativistic case, we extend the variational formalism for spheres with isotropic pressure developed by Chandrasekhar. We find that, in general, when the tangential pressure is greater than the radial pressure, the stability of the anisotropic sphere is enhanced when compared to isotropic configurations. In particular, anisotropic spheres are found to be stable for smaller values of the adiabatic index $γ$.

gr-qc↗
arXiv2002

Gauged Fermionic Q-balls

We present a new model for a non-topological soliton (NTS) that contains interacting fermions, scalar particles and a gauge field. Using a variational approach, we estimate the energy of the localized configuration, showing that it can be the lowest energy state of the system for a wide range of parameters.

hep-ph↗
arXiv2002

Long-lived oscillons from asymmetric bubbles

The possibility that extremely long-lived, time-dependent, and localized field configurations (``oscillons'') arise during the collapse of asymmetrical bubbles in 2+1 dimensional phi^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.

hep-th↗