Decay Of Domain Walls Research Articles

Transition to Fully or Partially Arrested State in Coupled Logistic Maps on a Ladder

Layered structures are an object of interest for theoretical and experimental reasons. In this work, we study coupled map lattice on a ladder. The ladder consists of two one-dimensional chains coupled at every point. We study linearly and nonlinearly coupled logistic maps in this system and study transition to nonzero persistence, in particular. We coarse-grain the variable value by assigning spin [Formula: see text] ([Formula: see text]) to sites that have value greater (less) than the fixed point and compute the number of sites that have not changed their spin values at all even times till the given time [Formula: see text]. The fraction of such sites at a given time [Formula: see text] is known as persistence. In our system, we observe a power-law of persistence at the critical value of coupling. This transition is also accompanied by long-range antiferromagnetic ordering for nonlinear coupling and long-range ferromagnetic ordering for linear coupling. The number of domain walls decay as [Formula: see text] at the critical point in both cases. The persistence exponent is 0.375 for a nonlinear case with two layers which is an exponent for the voter model on the ladder as well as for the Ising model at zero temperature or voter model in 1D. For linear coupling, we obtain a smaller persistence exponent.

Heavy dark matter and gravitational waves

We study the heavy dark matter produced around the temperature of the phase transition. Meanwhile domain walls can be formed after the breakdown of a ${\mathbb{Z}}_{3}$ discrete symmetry induced by the first-order phase transition. The generated gravitational waves by domain wall decay are found to be able to probed by the pulsar timing arrays, and the future square kilometer array.

Gravitational waves from first-order phase transition and domain wall

In many particle physics models, domain walls can form during the phase transition process after the breakdown of the discrete symmetry. Utilizing the ℤ3 symmetric complex singlet scalar extension of the Standard Model, we study the gravitational waves produced by the strongly first-order electroweak phase transition and the domain wall decay. The gravitational wave spectrum is of a typical two-peak shape. The high frequency peak corresponding to the strongly first-order electroweak phase transition is able to be probed by the future space-based interferometers, and the low frequency peak coming from the domain wall decay is far beyond the capability of the current Pulsar Timing Arrays, and future Square Kilometer Array.

QCD axion dark matter from long-lived domain walls during matter domination

The domain wall problem of the Peccei–Quinn mechanism can be solved if the Peccei–Quinn symmetry is explicitly broken by a small amount. Domain walls decay into axions, which may account for dark matter of the universe. This scheme is however strongly constrained by overproduction of axions unless the phase of the explicit breaking term is tuned. We investigate the case where the universe is matter-dominated around the temperature of the MeV scale and domain walls decay during this matter dominated epoch. We show how the viable parameter space is expanded.

Entropy production by domain wall decay in the NMSSM

We consider domain walls in the $Z_3$ symmetric NMSSM. The spontaneous $Z_3$ discrete symmetry breaking produces domain walls, and the stable domain walls are problematic. Thus, we assume the $Z_3$ symmetry is slightly but explicitly broken and the domain walls decay. Such a decay causes a large late-time entropy production. We study its cosmological implications on unwanted relics such as moduli, gravitino, LSP and axion.

Domain walls and vortices in chiral symmetry breaking

We study domain walls and vortices in chiral symmetry breaking in a QCD-like theory with N flavors in the chiral limit. If the axial anomaly is absent, there exist stable Abelian axial vortices winding around the spontaneously broken U(1)_A symmetry and non-Abelian axial vortices winding around both the U(1)_A and non-Abelian SU(N) chiral symmetries. In the presence of the axial anomaly term, metastable domain walls are present and Abelian axial vortices must be attached by N domain walls, forming domain wall junctions. We show that a domain wall junction decays into N non-Abelian vortices attached by domain walls, implying its metastability. We also show that domain walls decay through the quantum tunneling by creating a hole bounded by a closed non-Abelian vortex.

On the estimation of gravitational wave spectrum from cosmic domain walls

We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by the use of field theoretic lattice simulations with grid size 10243, which is larger than the previous study. We have recognized that there exists an error in the code used in the previous study, and the correction of the error leads to the suppression of the spectrum of gravitational waves at high frequencies. The peak of the spectrum is located at the scale corresponding to the Hubble radius at the time of the decay of domain walls, and its amplitude is consistent with the naive estimation based on the quadrupole formula. Using the numerical results, the magnitude and the peak frequency of gravitational waves at the present time are estimated. It is shown that for some choices of parameters the signal of gravitational waves is strong enough to be probed in the future gravitational wave experiments.

Study of gravitational radiation from cosmic domain walls

In this paper, following the previous study, we evaluate the spectrum of gravitational wave background generated by domain walls which are produced if some discrete symmetry is spontaneously broken in the early universe. We apply two methods to calculate the gravitational wave spectrum: One is to calculate the gravitational wave spectrum directly from numerical simulations, and another is to calculate it indirectly by estimating the unequal time anisotropic stress power spectrum of the scalar field. Both analysises indicate that the slope of the spectrum changes at two characteristic frequencies corresponding to the Hubble radius at the decay of domain walls and the width of domain walls, and that the spectrum between these two characteristic frequencies becomes flat or slightly red tilted. The second method enables us to evaluate the GW spectrum for the frequencies which cannot be resolved in the finite box lattice simulations, but relies on the assumptions for the unequal time correlations of the source.

Dynamics of domain walls for split and runaway potentials

We demonstrate that the evolution of wall-like inhomogeneities in runaway potentials, characteristic of dynamical supersymmetry breaking and moduli stabilization, is very similar to the evolution of domain-wall networks associated with double-well potentials. Instabilities that would lead to a rapid decay of domain walls can be significantly ameliorated by compensation effects between a nondegeneracy of the vacua and a biased initial distribution, which can be naturally expected in a wide class or particle physics models that lead to out-of-equilibrium phase transitions. Within this framework, it is possible to obtain domain walls that live long enough to be relevant for the cosmic power spectrum and galaxy clustering, while being compatible with the observed cosmic microwave background anisotropies.

Late-time entropy production due to the decay of domain walls

It is shown that late-time decay of domain walls can dilute unwanted relics such as moduli, if the universe was dominated by frustrated domain walls with tension σ=(1–100TeV)3. Since energy density of the frustrated domain walls decreases as slow as the inverse of the scale factor, an overclosure limit on the axion decay constant fa is also considerably relaxed. In fact fa can be as large as the Planck scale, which may enable us to naturally implement the QCD axion in the string scheme. Furthermore, in contrast to thermal inflation models, the Affleck–Dine baryogenesis can generate enough asymmetry to explain the present baryon abundance, even in the presence of late-time entropy production.

Puncture of gravitating domain walls

We investigate the semi-classical instability of vacuum domain walls to processes where the domain walls decay by the formation of closed string loop boundaries on their worldvolumes. Intuitively, a wall which is initially spherical may `pop', so that a hole corresponding to a string boundary component on the wall, may form. We find instantons, and calculate the rates, for such processes. We show that after puncture, the hole grows exponentially at the same rate that the wall expands. It follows that the wall is never completely thermalized by a single expanding hole; at arbitrarily late times there is still a large, thin shell of matter which may drive an exponential expansion of the universe. We also study the situation where the wall is subjected to multiple punctures. We find that in order to completely annihilate the wall by this process, at least four string loops must be nucleated. We argue that this process may be relevant in certain brane-world scenarios, where the universe itself is a domain wall.

Quantum decay of domain walls in cosmology. I. Instanton approach

This paper studies the decay of a large, closed domain wall in a closed universe. Such walls can form in the presence of a broken, discrete symmetry. We introduce a novel process of quantum decay for such a wall, in which the vacuum fluctuates from one discrete state to another throughout one half of the universe, so that the wall decays into pure field energy. Equivalently, the fluctuation can be thought of as the nucleation of a second domain wall of zero size, followed by its growth by quantum tunnelling and its collision with the first wall, annihilating both. The barrier factor for this quantum tunneling is calculated by guessing and verifying a Euclidean instanton for the two-wall system. We also discuss the classical origin and evolution of closed, topologically spherical domain walls in the early universe, through a "budding-off" process involving closed domain walls larger than the Hubble radius. This paper is the first of a series on this subject.

Quantum decay of domain walls in cosmology. II. Hamiltonian approach

This paper studies the decay of a large, closed domain wall in a closed universe. Such walls can form in the presence of a broken, discrete symmetry. We study a novel process of quantum decay for such a wall, in which the vacuum fluctuates from one discrete state to another throughout one half of the universe, so that the wall decays into pure field energy. Equivalently, the fluctuation can be thought of as the nucleation of a second closed domain wall of zero size, followed by its growth by quantum tunnelling and its collision with the first wall, annihilating both. We therefore study the 2-wall system coupled to a spherically symmetric gravitational field. We derive a simple form of the 2-wall action, use Dirac quantization, obtain the 2-wall wave function for annihilation, find from it the barrier factor for this quantum tunneling, and thereby get the decay probability. This is the second paper of a series.

Quantum field theory of non-abelian strings and vortices

We develop an operator formalism for investigating the properties of non-abelian cosmic strings (and vortices) in quantum field theory. Operators are constructed that introduce classical string sources and that create dynamical string loops. The operator construction in lattice gauge theory is explicitly described, and correlation functions are computed in the strong-coupling and weak-coupling limits. These correlation functions are used to study the long-range interactions of non-abelian strings, taking account of charge-screening effects due to virtual particles. Among the phenomena investigated are the Aharonov-Bohm interactions of strings with charged particles, holonomy interactions between string loops, string entanglement, the transfer of “Cheshire charge” to a string loop, and domain-wall decay via spontaneous string nucleation. We also anayze the Aharonov-Bohm interactions of magnetic monopoles with electric flux tubes in a confining gauge theory. We propose that the Aharonov-Bohm effect can be invoked to distinguish among various phases of a non-abelian gauge theory coupled to matter.