Alejandra Kandus

Primordial magnetic fields induced by cosmological particle creation

We study the primordial magnetic field generated by stochastic currents produced by scalar charged particles created at the beginning of the radiation dominated epoch. We find that, for the mass range

Cosmological magnetic fields from gauge-mediated supersymmetry-breaking models

{10}^{\ensuremath{-}6} \mathrm{GeV}\ensuremath{\lesssim}m\ensuremath{\lesssim}{10}^{2} \mathrm{GeV}

Superadiabatic-type magnetic amplification in conventional cosmology

, a field of sufficient intensity to seed different mechanisms of galactic magnetic field generation, while still consistent with observational and theoretical constraints, is created coherently over a galactic scale.

Self-consistent estimates of magnetic fields from reheating

Abstract We study the generation of primordial magnetic fields, coherent over cosmologically interesting scales, by gravitational creation of charged scalar particles during the reheating period. We show that magnetic fields consistent with those detected by observation may be obtained if the particle mean life τs is in the range 10−14 s ≲τs≲10−7 s. We apply this mechanism to minimal gauge-mediated supersymmetry-breaking models, in the case in which the lightest stau τ 1 is the next-to-lightest supersymmetric particle. We show that, for a large range of phenomenologically acceptable values of the supersymmetry-breaking scale F , the generated primordial magnetic field can be strong enough to seed the galactic dynamo.

Generalized Ohm's law for relativistic plasmas

We consider the evolution of cosmological magnetic fields in Friedmann-Robertson-Walker models and outline a geometrical mechanism for their superadiabatic amplification on large scales. The mechanism operates within standard electromagnetic theory and applies to Friedmann-Robertson-Walker universes with open spatial sections. We discuss the general relativistic nature of the effect and show how it modifies the adiabatic magnetic evolution. Assuming a universe that is only marginally open today, we estimate the main features of the superadiabatically amplified residual field.

Primordial magnetic helicity from stochastic electric currents

We investigate the generation of primordial magnetic fields from stochastic currents created by the cosmological transition from inflation to reheating. We consider N charged scalar fields coupled to the electromagnetic field in a curved background and derive self-consistent equations for the evolution of the two point functions of the fields, which in the large N limit give a decoupled set for the scalar and the electromagnetic functions. The main contribution to the electric current comes from the infrared portion of the spectrum of created particles, and in this limit the damping of the magnetic field is not due to normal conductivity but to London currents in the scalar field. For a given set of the physical parameters of the problem, we solved this equation numerically and found that, due to the fact that the London currents are oscillating, the field actually grows exponentially during the time interval in which our large-N limit equations are valid. Although for the chosen parameters the induced field is weak, the present uncertainties on their actual values leave open the possibility for higher intensities.

Primordial Magnetic Field Amplification from Turbulent Reheating

We generalize the relativistic expression of Ohms law by studying a multifluid system of charged species using the 1 + 3 covariant formulation of general relativistic electrodynamics. This is done by providing a fully relativistic, fully non-linear propagation equation for the spatial component of the electric 4-current. Our analysis proceeds along the lines of the non-relativistic studies and extends previous relativistic work on cold plasmas. Exploiting the compactness and transparency of the covariant formalism, we provide a direct comparison with the standard Newtonian versions of Ohms law and identify the relativistic corrections in an unambiguous way. The generalized expression of Ohms law is initially given relative to an arbitrary observer and for a multicomponent relativistic charged medium. Then, the law is written with respect to the Eckart frame and for a hot two-fluid plasma with zero total charge. Finally, we apply our analysis to a cold proton–electron plasma and recover the well-known magnetohydrodynamic expressions. In every step, we discuss the approximations made and identify familiar effects, like the Biermann battery and the Hall effect.

A Hydrodynamic Approach to the Study of Anisotropic Instabilities in Dissipative Relativistic Plasmas

Fil: Calzetta, Esteban Adolfo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Fisica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisica de Buenos Aires; Argentina

Non-conformal evolution of magnetic fields during reheating

We analyze the possibility of primordial magnetic field amplification by a stochastic large scale kinematic dynamo during reheating. We consider a charged scalar field minimally coupled to gravity. During inflation this field is assumed to be in its vacuum state. At the transition to reheating the state of the field changes to a many particle/anti-particle state. We characterize that state as a fluid flow of zero mean velocity but with a stochastic velocity field. We compute the scale-dependent Reynolds number Re(k), and the characteristic times for decay of turbulence, t{sub d} and pair annihilation t{sub a}, finding t{sub a} << t{sub d}. We calculate the rms value of the kinetic helicity of the flow over a scale L and show that it does not vanish. We use this result to estimate the amplification factor of a seed field from the stochastic kinematic dynamo equations. Although this effect is weak, it shows that the evolution of the cosmic magnetic field from reheating to galaxy formation may well be more complex than as dictated by simple flux freezing.

Analysis of the effect of a mean velocity field on a mean field dynamo

We develop a purely hydrodynamic formalism to describe collisional, anisotropic instabilities in a relativistic plasma, that are usually described with kinetic theory tools. Our main motivation is the fact that coarse-grained models of high particle number systems give more clear and comprehensive physical descriptions of those systems than purely kinetic approaches, and can be more easily tested experimentally as well as numerically. In particular, we aim at developing a theory that describes both a background non-equilibrium fluid configurations and its perturbations, to be able to account for the backreaction of the latter on the former. Our system of equations includes the usual conservation laws for the energy-momentum tensor and for the electric current, and the equations for two new tensors that encode the information about dissipation. To make contact with kinetic theory, we write the different tensors as the moments of a non-equilibrium one-particle distribution function (1pdf) which, for illustrative purposes, we take in the form of a Grad-like ansatz. Although this choice limits the applicability of the formalism to states not far from equilibrium, it retains the main features of the underlying kinetic theory. We assume the validity of the Vlasov-Boltzmann equation, with a collision integral given by the Anderson-Witting prescription, which is more suitable for highly relativistic systems than Marles (or Bhatnagar, Gross and Krook) form, and derive the conservation laws by taking its corresponding moments. We apply our developments to study the emergence of instabilities in an anisotropic, but axially symmetric background. For small departures of isotropy we find the dispersion relation for normal modes, which admit unstable solutions for a wide range of values of the parameter space.