Non-abelian plasma instabilities for strong anisotropy

We numerically investigate gauge field instabilities in anisotropic SU(2) plasmas using weak field initial conditions. The growth of unstable modes is stopped by non-abelian effects for moderate anisotropy. If we increase the anisotropy the growth continues beyond the non-abelian saturation bound. We find strong indications that the continued growth is not due to over-saturation of infrared field modes, but instead due to very rapid growth of high momentum modes which are not unstable in the weak field limit. The saturation amplitude strongly depends on the initial conditions. For strong initial fields we do not observe the sustained growth.Comment: 28 pages, 17 figure

Moduli decay in the hot early Universe

We consider moduli fields interacting with thermalized relativistic matter. We determine the temperature dependence of their damping rate and find it is dominated by thermal effects in the high temperature regime, i.e. for temperatures larger than their mass. For a simple scalar model the damping rate is expressed through the known matter bulk viscosity. The high temperature damping rate is always smaller than the Hubble rate, so that thermal effects are not sufficient for solving the cosmological moduli problem.Comment: Numerical error in the final result for the damping rate corrected, conclusions of the paper are not affecte

Sterile neutrino dark matter: impact of active-neutrino opacities

Bödeker D, Klaus A. Sterile neutrino dark matter: impact of active-neutrino opacities. Journal of High Energy Physics. 2020;2020(7): 218.The resonant production of keV sterile-neutrino dark matter mainly takes place during the QCD epoch of the early universe. It has been argued that it could be strongly affected by the opacities (or damping rates) of active neutrinos, which receive non-perturbative QCD-contributions. We find that for lepton asymmetries nL alpha/s below 10(-6) the opacities significantly affect the sterile-neutrino yield, but that for larger asymmetries, which are necessary for producing a significant fraction of the dark matter, the yield is insensitive to changes of the opacities. Thus non-perturbative QCD contributions to the opacities at temperatures around 160 MeV will not affect this dark matter scenario. We obtain larger sterile-neutrino yields than previous studies, and thus weaker lower limits on the active-sterile mixing angle from Big Bang Nucleosynthesis

A local Langevin equation for slow long-distance modes of hot non-Abelian gauge fields

The effective theory for the dynamics of hot non-Abelian gauge fields with spatial momenta of order of the magnetic screening scale g^2 T is described by a Boltzmann equation. The dynamical content of this theory is explored. There are three relevant frequency scales, g T, g^2 T and g^4 T, associated with plasmon oscillations, multipole fluctuations of color charge, and with the non-perturbative gauge field dynamics, respectively. The frequency scale g T is integrated out. The result is a local Langevin-type equation. It is valid to leading order in g and to all orders in log(1/g), and it does not suffer from the hard thermal loop divergences of classical thermal Yang-Mills theory. We then derive the corresponding Fokker-Planck equation, which is shown to generate an equilibrium distribution corresponding to 3-dimensional Yang-Mills theory plus a Gaussian free field.Comment: Typo in the formula for the effective Hamiltonian correcte

Order g(2) susceptibilities in the symmetric phase of the Standard Model

Bödeker D, Sangel M. Order g(2) susceptibilities in the symmetric phase of the Standard Model. Journal of Cosmology and Astroparticle Physics. 2015;2015(4):040.Susceptibilities of conserved charges such as baryon minus lepton number enter baryogenesis computations, since they provide the relationship between conserved charges and chemical potentials. Their next-to-leading order corrections are of order g, where g is a generic Standard Model coupling. They are due to soft Higgs boson exchange, and have been calculated recently, together with some order g(2) corrections. Here we compute the complete g(2) contributions. Close to the electroweak crossover the soft Higgs contribution is of order g(2), and is determined by the non-perturbative physics at the magnetic screening scale

Non-equilibrium field theory

I discuss various topics in relativistic non-equilibrium field theory related to high energy physics and cosmology. I focus on non-perturbative problems and how they can be treated on the lattice.Comment: Plenary talk given at the 18th International Symposium on Lattice Field Theory (Lattice 2000), Bangalore, India, 17-22 Aug 200

Cosmic QCD Epoch at Nonvanishing Lepton Asymmetry

Wygas M, Oldengott IM, Bödeker D, Schwarz D. Cosmic QCD Epoch at Nonvanishing Lepton Asymmetry. PHYSICAL REVIEW LETTERS. 2018;121(20): 201302.We investigate how a lepton asymmetry impacts the cosmic trajectory in the QCD phase diagram. We study the evolution of chemical potentials during the QCD epoch of the early Universe using susceptibilities from lattice QCD to interpolate between an ideal quark gas and an ideal hadron resonance gas. The lepton asymmetry affects the evolution of all chemical potentials. The standard cosmic trajectory is obtained assuming tiny lepton and baryon asymmetries. For larger lepton asymmetry, the charge chemical potential exceeds the baryon chemical potential before pion annihilation

Hard thermal loops for soft or collinear external momenta

We consider finite temperature 1-loop diagrams with hard loop momenta and an arbitrary number of external gauge fields when the external momenta are either soft, or near the light cone and nearly collinear with the loop momentum. We obtain a recursion relation for these diagrams which we translate into an equation for their generating functional. By integrating out the soft fields while keeping two collinear ones we find an integral equation, originally due to Arnold, Moore, and Yaffe, which sums the bremsstrahlung and pair annihilation contribution to the thermal photon production rate.Comment: 17 pages, title corrected, clarifying paragraph added to the appendix, version to appear in JHE

Non-relativistic leptogenesis

Bödeker D, Wörmann M. Non-relativistic leptogenesis. Journal of Cosmology and Astroparticle Physics. 2014;2014(02):016.In many phenomenologically interesting models of thermal leptogenesis the heavy neutrinos are non-relativistic when they decay and produce the baryon asymmetry of the Universe. We propose a non-relativistic approximation for the corresponding rate equations in the non-resonant case, and a systematic way for computing relativistic corrections. We determine the leading order coefficients in these equations, and the first relativistic corrections. The non-relativistic approximation works remarkably well. It appears to be consistent with results obtained using a Boltzmann equation taking into account the momentum distribution of the heavy neutrinos, while being much simpler. We also compute radiative corrections to some of the coefficients in the rate equations. Their effect is of order 1% in the regime favored by neutrino oscillation data. We obtain the correct leading order lepton number washout rate in this regime, which leads to large (~ 20%) effects compared to previous computations

The cosmic QCD transition for large lepton flavour asymmetries

We study the impact of large lepton flavour asymmetries on the cosmic QCD transition. Scenarios of unequal lepton flavour asymmetries are observationally almost unconstrained and therefore open up a whole new parameter space in order to study the nature of the cosmic QCD transition. For very large asymmetries, we point out two limitations to our current method, namely the possible formation of a Bose-Einstein condensate of pions and the reliability of the Taylor expansion applied in this work.Comment: 10 pages, 6 figure