arXiv subjects

Walter Grimus

Publications and source records attributed to Walter Grimus.

23 records · Page 2Linked to original sources

arXiv2005

Neutrino mass matrices, texture zeros, and family symmetries

We demonstrate that Abelian family symmetries allow one to enforce texture zeros in arbitrary entries of the fermion mass matrices. Placing zeros in any number of elements of all occurring mass matrices can be done with two alternative methods; one of them utilizes the group Z_n with n sufficiently high. Concentrating on the lepton sector and on neutrino masses, we discuss the methods in the case of seesaw models and scalar triplet models. As an illustration, we present an example for each type of model.

hep-ph↗

arXiv2005

Mu-tau antisymmetry and neutrino mass matrices

Using the seesaw mechanism and a discrete symmetry, we construct a class of models for the neutrino mass matrix where the inverse of that matrix is the sum of a mu-tau antisymmetric background and a perturbation. We consider various possibilities for that perturbation. The simplest possible perturbations lead to four-parameter neutrino mass matrices which are unable to fit the experimental data. More complicated perturbations give rise to viable six-parameter mass matrices; we present detailed predictions of each of them.

hep-ph↗

arXiv2005

Unitarity triangle test of the extra factor of two in particle oscillation phases

There are claims in the literature that in neutrino oscillations and oscillations of neutral kaons and B-mesons the oscillation phase differs from the standard one by a factor of two. We reconsider the arguments leading to this extra factor and investigate, in particular, the non-relativistic regime. We actually find that the very same arguments lead to an ambiguous phase and that the extra factor of two is a special case. We demonstrate that the unitarity triangle (UT) fit in the Standard Model with three families is a suitable means to discriminate between the standard oscillation phase and the phase with an extra factor of two. If $K_L - K_S$ and $B_{dH} - B_{dL}$ mass differences are extracted from the $K^0 - \bar K^0$ and $B_d^0 - \bar B_d^0$ data, respectively, with the extra factor of two in the oscillation phases, then the UT fit becomes significantly worse in comparison with the standard fit and the extra factor of two is disfavoured by the existing data at the level of more than 3 $σ$.

hep-ph↗

arXiv2005

Non-vanishing $U_{e3}$ and $\cos{2 θ_{23}}$ from a broken $Z_2$ symmetry

It is shown that the neutrino mass matrices in the flavour basis yielding a vanishing $U_{e3}$ are characterized by invariance under a class of $Z_2$ symmetries. A specific $Z_2$ in this class also leads to a maximal atmospheric mixing angle $θ_{23}$. The breaking of that $Z_2$ can be parameterized by two dimensionless quantities, $\e$ and $\e'$; the effects of $\e, \e' \neq 0$ are studied perturbatively and numerically. The induced value of $\ue3$ strongly depends on the neutrino mass hierarchy. We find that $\ue3$ is less than 0.07 for a normal mass hierarchy, even when $\e, \e' \sim 30 %$. For an inverted mass hierarchy $\ue3$ tends to be around 0.1 but can be as large as 0.17. In the case of quasi-degenerate neutrinos, $\ue3$ could be close to its experimental upper bound 0.2. In contrast, $| \cos{2θ_{23}} |$ can always reach its experimental upper bound 0.28. We propose a specific model, based on electroweak radiative corrections in the MSSM, for $\e$ and $\e'$. In that model, both $\ue3$ and $| \cos{2 θ_{23}} |$, could be close to their respective experimental upper bounds if neutrinos are quasi-degenerate.

hep-ph↗

arXiv1999

Neutrino oscillations and the effect of the finite lifetime of the neutrino source

We consider a neutrino source at rest and discuss a condition for the existence of neutrino oscillations which derives from the finite lifetime $τ_S$ of the neutrino source particle. This condition is present if the neutrino source is a free particle such that its wave function is non-stationary. For a Gaussian wave function and with some simplifying assumptions, we study the modification of the usual oscillation probability stemming from $τ_S$. In the present accelerator experiments the effect of $τ_S$ can be neglected. We discuss some experimental situations where the source lifetime becomes relevant in the oscillation formula.

hep-ph↗