Dynamics of tachyonic preheating after hybrid inflation

We study the instability of a scalar field at the end of hybrid inflation, using both analytical techniques and numerical simulations. We improve previous studies by taking the inflaton field fully into account, and show that the range of unstable modes depends sensitively on the velocity of the inflaton field, and thereby on the Hubble rate, at the end of inflation. If topological defects are formed, their number density is determined by the shortest unstable wavelength. Finally, we show that the oscillations of the inflaton field amplify the inhomogeneities in the energy density, leading to local symmetry restoration and faster thermalization. We believe this explains why tachyonic preheating is so effective in transferring energy away from the inflaton zero mode.Comment: 12 pages, 10 figures, REVTeX. Minor changes, some references added. To appear in PR

Topological Defects from First Order Gauge Theory Phase Transitions

We investigate the mechanism by which topological defects form in first order phase transitions with a charged order parameter. We show how thick superconductor vortices and heavy cosmic strings form by trapping of magnetic flux. In an external magnetic field, intermediate objects such as strips and membranes of magnetic flux and chains of single winding defects are produced. At non-zero temperature, a variety of spontaneous defects of different winding numbers arise. In cosmology, our results mean that the magnetic flux thermal fluctuations get trapped in a primordial multi-tension string network. The mechanism may also apply to the production of cosmic-like strings in brane collisions. In a thin type-I superconductor film, flux strips are found to be meta-stable while thick vortices are stable up to some critical value of the winding number which increases with the thickness of the film. In addition, a non-dissipative Josephson-like current is obtained across the strips of quantized magnetic flux.Comment: Corrections made on sections 4,5. Higher quality figures in published versio

Cusps on cosmic superstrings with junctions

The existence of cusps on non-periodic strings ending on D-branes is demonstrated and the conditions, for which such cusps are generic, are derived. The dynamics of F-, D-string and FD-string junctions are investigated. It is shown that pairs of FD-string junctions, such as would form after intercommutations of F- and D-strings, generically contain cusps. This new feature of cosmic superstrings opens up the possibility of extra channels of energy loss from a string network. The phenomenology of cusps on such cosmic superstring networks is compared to that of cusps formed on networks of their field theory analogues, the standard cosmic strings.Comment: 22 pages, 5 figure

Estimation of vortex density after superconducting film quench

This paper addresses the problem of vortex formation during a rapid quench in a superconducting film. It builds on previous work showing that in a local gauge theory there are two distinct mechanisms of defect formation, based on fluctuations of the scalar and gauge fields, respectively. We show how vortex formation in a thin film differs from the fully two-dimensional case, on which most theoretical studies have focused. We discuss ways of testing theoretical predictions in superconductor experiments and analyse the results of recent experiments in this light.Comment: 7 pages, no figure

Numerical experiments with p F- and q D-strings: the formation of (p,q) bound states

We investigate the behaviour of (p,q) string networks, focusing on two aspects: (1) modelling more realistic (p,q) string networks than the Z_N networks used so far and (2) investigating the effect of long-range interactions on the evolution of the network. We model the network with no long-range interactions using two sets of fields, complex scalars coupled to gauge fields, with a potential chosen such that the two types of strings will form bound states. This way we can model junctions of 3 strings with different tension; in Z_N models used so far in simulations all the strings have identical tensions. In order to introduce long-range interactions we also study a network in which one of the scalars forms global strings. We observe that in the absence of long-range interactions the formation of bound states has a significant influence on the evolution of the network. When long-range interactions are turned on the bound states are short-lived and have a minimal effect on the network evolution.Comment: 17 pages, 8 figures, JCAP styl

Dynamics of F/D networks: the role of bound states

We study, via numerical experiments, the role of bound states in the evolution of cosmic superstring networks, being composed by p F-strings, q D-strings and (p,q) bound states. We find robust evidence for scaling of all three components of the network, independently of initial conditions. The novelty of our numerical approach consists of having control over the initial abundance of bound states. This indeed allows us to identify the effect of bound states on the evolution of the network. Our studies also clearly show the existence of an additional energy loss mechanism, resulting to a lower overall string network energy, and thus scaling of the network. This new mechanism consists of the formation of bound states with an increasing length.Comment: 8 pages, 13 figure

Formation of topological defects in gauge field theories

When a symmetry gets spontaneously broken in a phase transition, topological defects are typically formed. The theoretical picture of how this happens in a breakdown of a global symmetry, the Kibble-Zurek mechanism, is well established and has been tested in various condensed matter experiments. However, from the viewpoint of particle physics and cosmology, gauge field theories are more relevant than global theories. In recent years, there have been significant advances in the theory of defect formation in gauge field theories, which make precise predictions possible, and in experimental techniques that can be used to test these predictions in superconductor experiments. This opens up the possibility of carrying out relatively simple and controlled experiments, in which the non-equilibrium phase transition dynamics of gauge field theories can be studied. This will have a significant impact on our understanding of phase transitions in the early universe and in heavy ion collider experiments. In this paper, I review the current status of the theory and the experiments in which it can be tested.Comment: Review article, 43 pages, 7 figures. Minor changes, some references added. Final version to appear in IJMP

Cosmic Strings and Superstrings

Cosmic strings are predicted by many field-theory models, and may have been formed at a symmetry-breaking transition early in the history of the universe, such as that associated with grand unification. They could have important cosmological effects. Scenarios suggested by fundamental string theory or M-theory, in particular the popular idea of brane inflation, also strongly suggest the appearance of similar structures. Here we review the reasons for postulating the existence of cosmic strings or superstrings, the various possible ways in which they might be detected observationally, and the special features that might discriminate between ordinary cosmic strings and superstrings.Comment: Minor errors corrected and some references added, 34 pages, 6 figure

Symmetry Breaking and False Vacuum Decay after Hybrid Inflation

We discuss the onset of symmetry breaking from the false vacuum in generic scenarios in which the mass squared of the symmetry breaking (Higgs) field depends linearly with time, as it occurs, via the evolution of the inflaton, in models of hybrid inflation. We show that the Higgs fluctuations evolve from quantum to classical during the initial stages. This justifies the subsequent use of real-time lattice simulations to describe the fully non-perturbative and non-linear process of symmetry breaking. The early distribution of the Higgs field is that of a smooth classical gaussian random field, and consists of lumps whose shape and distribution is well understood analytically. The lumps grow with time and develop into ``bubbles'' which eventually collide among themselves, thus populating the high momentum modes, in their way towards thermalization at the true vacuum. With the help of some approximations we are able to provide a quasi-analytic understanding of this process.Comment: 33 pages, 16 figures, LaTeX, uses revtex. Version to be published in Phys. Rev. with minor change