Joern Kersten

Running neutrino mass parameters in see-saw scenarios

We systematically analyze quantum corrections in see-saw scenarios, including effects from above as well as below the see-saw scales. We derive approximate renormalization group equations for neutrino masses, lepton mixings and CP phases, yielding an analytic understanding and a simple estimate of the size of the effects. Even for hierarchical masses, they often exceed the precision of future experiments. Furthermore, we provide a software package allowing for a convenient numerical renormalization group analysis, with heavy singlets being integrated out successively at their mass thresholds. We also discuss applications to model building and related topics.

Neutrino mass operator renormalization in two Higgs doublet models and the MSSM

In a recent re-analysis of the Standard Model (SM) (β)-function for the effective neutrino mass operator, we found that the previous results were not entirely correct. Therefore, we consider the analogous dimension five operators in a class of two Higgs doublet models (2HDMs) and the minimal supersymmetric Standard Model (MSSM). Deriving the renormalization group equations for these effective operators, we confirm the existing result in the case of the MSSM. Some of our 2HDM results are new, while others differ from earlier calculations. This leads to modifications in the renormalization group evolution of leptonic mixing angles and CP phases in the 2HDMs.

Neutrino mass matrix running for non-degenerate see-saw scales

We consider the running of the neutrino mass matrix in the Standard Model and the Minimal Supersymmetric Standard Model, extended by heavy singlet Majorana neutrinos. Unlike previous studies, we do not assume that all of the heavy mass eigenvalues are degenerate. This leads to various effective theories when the heavy degrees of freedom are integrated out successively. We calculate the Renormalization Group Equations that govern the evolution of the neutrino mass matrix in these effective theories. We show that an appropriate treatment of the singlet mass scales can yield a substantially different result compared to integrating out the singlets at a common intermediate scale.

The LMA solution from bimaximal lepton mixing at the GUT scale by renormalization group running

Abstract We show that in see-saw models with bimaximal lepton mixing at the GUT scale and with zero CP phases, the solar mixing angle θ 12 generically evolves towards sizably smaller values due to renormalization group effects, whereas the evolution of θ 13 and θ 23 is comparatively small. The currently favored LMA solution of the solar neutrino problem can thus be obtained in a natural way from bimaximal mixing at the GUT scale. We present numerical examples for the evolution of the leptonic mixing angles in the Standard Model and the MSSM, in which the current best-fit values of the LMA mixing angles are produced. These include a case where the mass eigenstates corresponding to the solar mass squared difference have opposite CP parity.

Tight bonds between sterile neutrinos and dark matter

Despite the astonishing success of standard ΛCDM cosmology, there is mounting evidence for a tension with observations at small and intermediate scales. We introduce a simple model where both cold dark matter (DM) and sterile neutrinos are charged under a new U(1){sub X} gauge interaction. The resulting DM self-interactions resolve the tension with the observed abundances and internal density structures of dwarf galaxies. At the same time, the sterile neutrinos can account for both the small hot DM component favored by cosmological observations and the neutrino anomalies found in short-baseline experiments.

Is there maximal mixing in the lepton sector

We discuss the potential of long-baseline neutrino oscillation experiments to determine deviations from maximal {nu}{sub {mu}}-{nu}{sub {tau}} mixing. We compare the obtainable sensitivities to predictions from neutrino mass models and to the size of quantum corrections. We find that the theoretical expectations for deviations are typically well within experimental reach.

Dark matter from gaugino mediation

We study dark matter (DM) for gaugino-mediated supersymmetry breaking and compact dimensions of order of the grand unification scale. Higgs fields are bulk fields and in general their masses differ from those of squarks and sleptons at the unification scale. As a consequence, at different points in parameter space, the gravitino, a neutralino or a scalar lepton can be the lightest (LSP) or next-to-lightest (NLSP) superparticle. We investigate the constraints from primordial nucleosynthesis on the different scenarios. While neutralino DM and gravitino DM with a NLSP are consistent for a wide range of parameters, gravitino DM with a NLSP is strongly constrained. Gravitino DM with a χ0 NLSP is excluded.

Squarks and sleptons between branes and bulk

We study gaugino-mediated supersymmetry breaking in a six-dimensional SO(10) orbifold GUT model where quarks and leptons are mixtures of brane and bulk fields. The couplings of bulk matter fields to the supersymmetry breaking brane field have to be suppressed in order to avoid large FCNCs. We derive bounds on the soft supersymmetry breaking parameters and calculate the superparticle mass spectrum. If the gravitino is the LSP, the 1 or the τL turns out to be the NLSP, with characteristic signatures at future colliders and in cosmology.

Suppressing structure formation at dwarf galaxy scales and below: late kinetic decoupling as a compelling alternative to warm dark matter

Warm dark matter cosmologies have been widely studied as an alternative to the cold dark matter paradigm, the characteristic feature being a suppression of structure formation on small cosmological scales. A very similar situation occurs if standard cold dark matter particles are kept in local thermal equilibrium with a, possibly dark, relativistic species until the universe has cooled down to keV temperatures. We perform a systematic phenomenological study of this possibility, and classify all minimal models containing dark matter and an arbitrary radiation component that allow such a late kinetic decoupling. We recover explicit cases recently discussed in the literature and identify new classes of examples that are very interesting from a model-building point of view. In some of these models dark matter is inevitably self-interacting, which is remarkable in view of recent observational support for this possibility. Hence, dark matter models featuring late kinetic decoupling have the potential not only to alleviate the missing satellites problem but also to address other problems of the cosmological concordance model on small scales, in particular the cusp-core and too-big-too-fail problems, in some cases without invoking any additional input.

Stability of texture zeros under radiative corrections in see-saw models

It has been shown that only certain neutrino mass matrices with texture zeros are compatible with existing data. We discuss the stability of phenomenological consequences of texture zeros under radiative corrections in the type-I see-saw scenario. We show that under certain conditions additional patterns are allowed due to these effects.