arXiv subjects

Anders Basboll

Publications and source records attributed to Anders Basboll.

8 recordsLinked to original sources

arXiv2010

Decaying neutrinos: The long way to isotropy

We investigate a scenario in which neutrinos are coupled to a pseudoscalar degree of freedom $\ph$ and where decays $ν_1 \to ν_2+\ph$ and inverse decays are the responsible mechanism for obtaining equilibrium. In this context we discuss the implication of the invisible neutrino decay on the neutrino-pseudoscalar coupling constant and the neutrino lifetime. Assuming the realistic scenario of a thermal background of neutrinos and pseudoscalar we update the bound on the (off-diagonal) neutrino-pseudoscalar coupling constant to $g<2.6\times10^{-13}$ and the bound on the neutrino lifetime to $τ<1\times10^{13}\,\rm{s}$. Furthermore we confirm analytically that kinetic equilibrium is delayed by two Lorentz $\ga$--factors -- one for time dilation of the (decaying) neutrino lifetime and one from the opening angle. We have also confirmed this behavior numerically.

astro-ph.CO↗

arXiv2010

$ν$MSSM superpotential to 6th order - normalised and with no superfluous couplings

We expand the superpotential of $ν$MSSM to 6th order. This is the order at which all flat directions can be lifted. All 5179 couplings are independent ie. the superpotential cannot be zero for all fields, without all couplings being zero. Likewise, any gauge invariant potential to the 6th order can be made by fixing the constants. A specific and welldefined choice of normalisation has been adopted. The case for investigating this potential, rather than looking at one or several generalised flat directions is made.

hep-ph↗

arXiv2010

SUSY Flat Direction Decay - the prospect of particle production and preheating investigated in the unitary gauge

We look at the possibility of non-perturbative particle production after inflation from SUSY flat directions produced by rotating eigenstates thereby avoiding the standard adiabaticity conditions. This might lead to preheating and prevent the delay of thermalisation of the universe. We investigate the flat directions $LLE^c$ and $U^cD^cD^c$ and find no particle production. These 2 directions are very important, since they have been named as possible candidates for being the inflaton. We investigate $QLQLQLE^c$ and find particle production and therefore the possibility of preheating. We investigate the $LLE^c$ and $U^cD^cD^c$ directions appearing simultaneously, and find no production. Finally, we investigate $LLE^c$ and $QLD^c$ simultaneously - with one L-field in common. Here we do find particle production and therefore the possibility of preheating. This means that if SUSY flat directions are to delay thermalisation and thus explain the (lack of) gravitino production, it is necessary to explain why complicated directions as $QLQLQLE^c$ are not exited, and why combinations like $LLE^c$ and $QLD^c$ are not both exited.

hep-th↗

arXiv2010

A complete and minimal catalogue of MSSM gauge invariant monomials

We present a complete and minimal catalogue of MSSM gauge invariant monomials. That is, the catalogue of Gherghetta, Kolda and Martin is elaborated to include generational structure for all monomials. Any gauge invariant operator can be built as a linear combination of elements of the catalogue lifted to nonnegative integer powers. And the removal of any one of the monomials would deprive the catalogue of this feature. It contains 712 monomials - plus 3 generations of righthanded neutrinos if one extends the model to the $ν$MSSM. We note that $ν$MSSM flat directions can all be lifted by the 6th order superpotential - compared to the 9th order needed in MSSM.

hep-ph↗

arXiv2009

SUSY Flat Directions -- to get a VEV or not?

We investigate the potential of SUSY flat directions (FDs). Large FD vacuum expectation values (VEVs) can delay thermalisation and solve the gravitino problem - if FDs decay perturbatively. This depends on how many and which directions get the VEVs. Recently the decay of the FDs have been studied with the VEVs as input. Here we look at how the VEVs come about -- statistically and analytically.

hep-ph↗

arXiv2008

Are cosmological neutrinos free-streaming?

Precision data from cosmology suggest neutrinos stream freely and hence interact very weakly around the epoch of recombination. We study this issue in a simple framework where neutrinos recouple instantaneously and stop streaming freely at a redshift z_i. The latest cosmological data imply z_i < 1500, the exact constraint depending somewhat on the assumed prior on z_i. This bound translates into a limit on the coupling strength between neutrinos and majoron-like particles phi, implying tau > 1 x 10^10 s (m_2/50 meV)^3 for the decay nu_2 -> nu_1+phi.

astro-ph↗

arXiv2008

Non-Perturbative Flat Direction Decay

We argue that supersymmetric flat direction vacuum expectation values can decay non-perturbatively via preheating. Considering a toy U(1) gauge theory, we explicitly calculate the scalar potential, in the unitary gauge, for excitations around several flat directions. We show that the mass matrix for the excitations has non-diagonal entries which vary with the phase of the flat direction vacuum expectation value. Furthermore, this mass matrix has zero eigenvalues whose eigenstates change with time. We show that these light degrees of freedom are produced copiously in the non-perturbative decay of the flat direction vacuum expectation value.

hep-ph↗

arXiv2006

Decay of heavy Majorana neutrinos using the full Boltzmann equation including its implications for leptogenesis

We have studied the two-body production and decay of a heavy, right-handed neutrino to two light states using the full Boltzmann equation instead of the usual integrated Boltzmann equation which assumes kinetic equilibrium of all species. Decays and inverse decays are inefficient for thermalising the distribution function of the heavy neutrino and in some parameter ranges there can be very large deviations from kinetic equilibrium. This leads to substantial numerical differences between the two approaches. Furthermore we study the impact of this difference on the lepton asymmetry production during leptogenesis and find that in the strong washout regime the final asymmetry is changed by 15-30% when the full Boltzmann equation is used.

hep-ph↗