arXiv subjects

Jarkko Ahonen

Publications and source records attributed to Jarkko Ahonen.

4 recordsLinked to original sources

arXiv1998

Transport coefficients in the early universe

We calculate numerically the electrical conductivity $σ$, heat conductivity $κ$ and shear viscosity $η$ of the hot plasma present in the early universe for the temperature interval $1\MeV\lsim T\lsim 10\GeV$. We use the Boltzmann collision equation to compute all the scattering matrix elements and regulate them by the thermal masses of the $t$- and $u$-channel particles. No leading order approximation is needed because of the numerical integration routines used.

hep-ph↗

arXiv1997

Magnetic field generation in first order phase transition bubble collisions

We consider the formation of a ring-like magnetic field in collisions of bubbles of broken phase in an abelian Higgs model. Particular attention is paid on multiple collisions. The small collision velocity limit, appropriate to the electroweak phase transition, is discussed. We argue that after the completion of the electroweak phase transition, when averaged over nucleation center distances, there exists a mean magnetic field $B\simeq 2.0\times 10^{20}$ G with a coherence length $9.1 \times 10^3 GeV^{-1}$ (for m_H=68 GeV). Because of the ring-like nature of B, the volume average behaves as $B \sim 1/L$. Taking into account the turbulent enhancement of the field by inverse cascade, we estimate that colliding electroweak bubbles would give rise to a mean field $B_{rms}\simeq 10^{-21}$ G at 10 Mpc comoving scale today.

hep-ph↗

arXiv1996

Electrical conductivity in the early universe

We solve numerically the Boltzmann equation in the early universe in the presence of a constant electric field and find the electrical conductivity $σ$ in the range $1\MeV\lsim T\lsim M_W$. The main contribution to $σ$ is shown to be due to leptonic interactions. For $T\lsim 100\MeV$ we find $σ\simeq 0.76T$ while at $T\simeq M_W$ we obtain $σ\simeq 6.7T$

hep-ph↗

arXiv1995

The paradox of axions surviving primordial magnetic fields

In the presence of primordial magnetic fields the oscillating cosmic axion field drives an oscillating electric field. The ensuing dissipation of axions is found to be inversely proportional to the conductivity of the primordial plasma. This counterintuitive result is essentially equivalent to ``Zeno's paradox'' or the ``watched-pot effect'' of quantum mechanics. It implies that the standard predictions of the cosmic axion density remain unaltered even if primordial magnetic fields are strong.

hep-ph↗