arXiv subjects

Anne-Christine Davis

Publications and source records attributed to Anne-Christine Davis.

142 records · Page 8Linked to original sources

arXiv1997

Cosmic String Zero Modes and Multiple Phase Transitions

The zero modes and current carrying capability of a cosmic string formed at one phase transition can be modified at subsequent phase transitions. A new, generalised index theorem is derived that is applicable to theories with multiple phase transitions. This enables us to investigate the fate of string zero modes during sequences of phase transitions in a variety of models. Depending on the couplings that the breaking introduces, the zero modes may be destroyed and the superconductivity of the string removed, and thus vortons dissipate. We discuss the features of the theory that are required to produce this behaviour and consider the implications of spectral flow.

hep-ph↗

arXiv1997

Friction Domination with Superconducting Strings

We investigate the evolution of a superconducting string network with arbitrary, constant string current in the friction dominated regime. In the absence of an external magnetic field the network always reaches a scaling solution. However, for string current stronger than a critical value, it is different than the usual, horizon-scaling of the non-superconducting string case. In this case the friction domination era never ends. Whilst the superconducting string network can be much denser than usually assumed, it can never dominate the universe energy density. It can, however, influence the cosmic microwave background radiation and the formation of large scale structure. When embedded in a primordial magnetic field of sufficient strength, the network never reaches scaling and, thus, eventually dominates the universe evolution.

hep-ph↗

arXiv1997

N=1 Supersymmetric Cosmic Strings

We investigate the microphysics of supersymmetric cosmic strings. In particular we focus on the vortices admitted by N=1 supersymmetric abelian Higgs models. We find the vortex solutions and demonstrate that the two simplest supersymmetric cosmic string models admit fermionic superconductivity. Further, by using supersymmetry transformations, we show how to solve for the fermion zero modes giving rise to string superconductivity in terms of the background string fields.

hep-ph↗

arXiv1997

Microphysics of SO(10) Cosmic Strings

We uncover a rich microphysical structure for SO(10) cosmic strings. For the abelian string the electroweak symmetry is restored around it in a region depending on the electroweak scale. A rich structure of nonabelian strings is found. Some of these also restore the electroweak symmetry. We investigate the zero mode structure of our strings. Whilst there are right handed neutrino zero modes for the abelian string, they do not survive the electroweak phase transition. In general the nonabelian strings do not have fermion zero modes. We consider the generalisation of our results to other theories and consider cosmological consequences of them.

hep-ph↗

arXiv1996

Dissipating Cosmic Vortons and Baryogenesis

Grand unified theories can admit cosmic strings with fermion zero modes which result in the string carrying a current and the formation of stable remnants, vortons. We consider theories in which the zero modes do not survive a subsequent phase transition, for example the electroweak transition, resulting in vorton dissipation. The dissipating vortons can create a baryon asymmetry. We calculate the asymmetry produced, and show that it is maximised if the vortons decay just before they dominate the energy density of the Universe. We further bound the asymmetry produced by the late decay of any relic particle.

hep-ph↗

arXiv1996

Generic Current-Carrying Strings

We investigate the standard model in a cosmic string background and show that the electroweak symmetry is partially restored. For a range of parameters the electroweak Higgs field can wind in this region, producing an electroweak string stabilised by the cosmic string background. In this case there are quark and lepton zero modes that result in the string becoming superconducting at the electroweak scale. If the electroweak Higgs field does not wind, there are no zero modes, but there are fermion bound states. These bound states can also carry a current.

hep-ph↗

arXiv1996

The Impossibility of Baryogenesis at a Second Order Electroweak Phase Transition

We investigate whether baryogenesis is possible at a second order electroweak phase transition. We find that under rather general conditions, the departure from thermal equilibrium is suppressed by the expansion rate of the Universe, and hence baryon production is also suppressed by the expansion rate. We conclude that if no additional sources of departure from thermal equilibrium such as topological defects are present, then electroweak baryogenesis is ruled out if the phase transition is second order or crossover. However, a non-vanishing net baryon to entropy ratio {\it is} generated, and we provide both upper and lower bounds for the result. Our technique is also applicable to other baryogenesis mechanisms taking place during and immediately after a second order phase transition. We estimate the lowest value of the transition energy scale for which the resulting baryon to entropy ratio might be large enough to explain observations.

hep-ph↗

arXiv1995

Constraining Supersymmetric SO(10) Models Through Cosmology

We study the impact of the symmetry breaking patterns from supersymmetric SO(10) down to the standard model on the standard big-bang cosmology through the formation of topological defects. None of the models is consistent with the standard cosmology without invoking any mechanism to solve the monopole problem. For this purpose, we use a hybrid false vacuum inflationary scenario. Only two symmetry breaking patterns are consistent with these topological considerations and with the actual data on the proton lifetime.

hep-ph↗

arXiv1995

Cosmic Strings are Current-Carrying

A synthesis of previous work done on the microscopic structure of cosmic strings in realistic models is made and reveals that strings are expected to be not only superconducting in the sense of Witten, but also generically current-carrying, either at the GUT scale or at the electroweak scale. This applies to any GUT string forming model leading to the standard electroweak theory as a low energy limit. The current consists of charged vector bosons. Cosmological consequences are briefly discussed.

hep-ph↗

arXiv1995

EMBEDDED DEFECTS AND SYMMETRY BREAKING IN FLIPPED $SU(5)$

We explicitly show the analogy between the symmetry breaking scheme for the GUT flipped $SU(5)$ with that of the Weinberg-Salam theory of electroweak interactions. This allows us to construct the embedded defect spectrum of the theory flipped $SU(5)$. We find that the spectrum consists of twelve gauge-equivalent unstable Lepto-quark strings, which are analogous to W-strings in electroweak theory, and another string that is gauge inequivalent to the Lepto-quark strings, which we call the `V-string'. The V-string is analogous to the Z-string of electroweak theory, correspondingly admitting a stable semilocal limit. Using data on the running coupling constants we indicate that in the non-supersymmetric case V-strings can be stable for part of the physically-viable parameter space. Cosmological consequences are briefly discussed.

hep-ph↗

arXiv1995

Nucleosynthesis Constraints on Defect-Mediated Electroweak Baryogenesis

In the defect-mediated electroweak baryogenesis scenario, baryons are produced in well separated regions of space. It is shown that between the electroweak phase transition at a temperature of $T \sim 100 {\rm GeV}$ and the end of nucleosynthesis at $T \sim 1 {\rm KeV}$ the baryon inhomogeneities dissipate, and that no constraints on defect-mediated electroweak baryogenesis can be derived from considerations of inhomogeneous nucleosynthesis.

astro-ph↗

arXiv1994

Local and Nonlocal Defect-Mediated Electroweak Baryogenesis

We consider the effects of particle transport in the topological defect-mediated electroweak baryogenesis scenarios of Ref. 1. We analyze the cases of both thin and thick defects and demonstrate an enhancement of the original mechanism in both cases due to an increased effective volume in which baryogenesis occurs. This phenomenon is a result of imperfect cancellation between the baryons and antibaryons produced on opposite faces of the defect.

hep-ph↗

arXiv1994

Formation of Topological Defects in a Second Order Phase Transition

The classical evolution equations of the Abelian Higgs model are studied at temperatures below the Ginsburg temperature of a phase transition which is assumed to be second order. It is shown that the initial thermal fluctuations provide a domain structure which is stable against late time fluctuations. This result lends support to the Kibble mechanism for the formation of topological defects.

hep-ph↗

arXiv1992

Electroweak Baryogenesis with a Second Order Phase Transition

If stable electroweak strings are copiously produced during the electroweak phase transition, they may contribute significantly to the presently observed baryon to entropy ratio of the universe. This analysis establishes the feasibility of implementing an electroweak baryogenesis scenario without a first order phase transition.

hep-ph↗

arXiv1992

Superconducting Cosmc Strings and Primordial Magnetic Fields

We consider grand unified theories with superconducting cosmic strings and which admit the mechanism for generating primordial magnetic fields recently discussed by Vachaspati. We show that these models are severely constrained by cosmological arguments. Quite generically, either stable springs or vortons will form. Provided the mass per unit length of the strings is sufficiently large, these stable configurations will overclose the Universe.

hep-ph↗

arXiv1992

Electroweak Baryogenesis with Electroweak Strings

If stable electroweak strings are copiously produced during the electroweak phase transition, they may contribute significantly to the presently observed baryon to entropy ratio of the Universe. This analysis establishes the feasibility of implementing an electroweak baryogenesis scenario without a first order phase transition.

astro-ph↗