Nuria Rius

Present and future bounds on non-standard neutrino interactions

We consider Non-Standard neutrino Interactions (NSI), described by four-fermion operators of the form (αγνβ)(γf), where f is an electron or first generation quark. We assume these operators are generated at dimension ≥ 8, so the related vertices involving charged leptons, obtained by an SU(2) transformation νδ→eδ, do not appear at tree level. These related vertices necessarily arise at one loop, via W exchange. We catalogue current constraints from sin 2θW measurements in neutrino scattering, from atmospheric neutrino observations, from LEP, and from bounds on the related charged lepton operators. We estimate future bounds from comparing KamLAND and solar neutrino data, and from measuring sin 2θW at the near detector of a neutrino factory. Operators constructed with νμ and νe should not confuse the determination of oscillation parameters at a νfactory, because the processes we consider are more sensitive than oscillations at the far detector. For operators involving ντ, we estimate similar sensitivities at the near and far detector.

Geometric approach to condensates in holographic QCD

An SU(N{sub f})xSU(N{sub f}) Yang-Mills theory on an extra-dimensional interval is considered, with appropriate symmetry-breaking boundary conditions on the IR brane. UV-brane to UV-brane correlators at high energies are compared with the OPE of two-point functions of QCD quark currents. Condensates correspond to departure from the AdS metric of the (different) metrics felt by vector and axial combinations, away from the UV brane. Their effect on hadronic observables is studied: the extracted condensates agree with the signs and orders of magnitude expected from QCD.

Aidnogenesis via leptogenesis and dark sphalerons

We discuss aidnogenesis,1 i.e. the generation of a dark matter asymmetry, via new sphaleron processes associated to an extra non-abelian gauge symmetry common to both the visible and the dark sectors. Such a theory can naturally produce an abundance of asymmetric dark matter which is of the same size as the lepton and baryon asymmetries, as suggested by the similar sizes of the observed baryonic and dark matter energy content, and provide a definite prediction for the mass of the dark matter particle. We discuss in detail a minimal realization in which the Standard Model is only extended by dark matter fermions which form “dark baryons” through an SU(3) interaction, and a (broken) horizontal symmetry that induces the new sphalerons. The dark matter mass is predicted to be ∼ 6 GeV, close to the region favored by DAMA and CoGeNT. Furthermore, a remnant of the horizontal symmetry should be broken at a lower scale and can also explain the Tevatron dimuon anomaly.

Leptonic CP violating asymmetries in Z0 decays

We show that CP conservation may be violated in the leptonic decays of the Z0 to a level that may be probed at LEP. We find that there may exist decay asymmetries ηij=BR(Z0→ei+ej)−BR(Z0→ej+ei) as large as O(10−7–10−8), where one of the charged leptons is a τ and the other is an e or μ. Such a value is consistent with all information about neutrino physics and the structure of the leptonic weak interaction and could arise in a simple extension of the standard SU(2) ⊗ U(1) model.

The Zee–Babu model revisited in the light of new data

We update previous analyses of the Zee–Babu model in the light of new data, e.g., the mixing angle θ13, the rare decay μ → eγ and the LHC results. We also analyze the possibility of accommodating the deviations in Γ( H → γγ) hinted by the LHC experiments, and the stability of the scalar potential. We find that neutrino oscillation data and low energy constraints are still compatible with masses of the extra charged scalars accessible to LHC. Moreover, if any of them is discovered, the model can be falsified by combining the information on the singly and doubly charged scalar decay modes with neutrino data. Conversely, if the neutrino spectrum is found to be inverted and the CP phase δ is quite different from π , the masses of the charged scalars will be well outside the LHC reach.

Finite temperature effects on CP violating asymmetries

We compute the CP violating decay asymmetries relevant for baryogenesis scenarios involving the out of equilibrium decays of heavy particles, including the finite temperature effects arising from the background of light thermal particles which are present during the decay epoch. Thermal effects can modify the size of CP violation by a sizeable fraction in the decay of scalar particles, but we find interesting cancellations in the thermal corrections affecting the asymmetries in the decays of fermions, as well as in the decay of scalars in supersymmetric theories. We also estimate the effects which arise from the motion of the decaying particles with respect to the background plasma.

Tau spin correlations at the Z peak. Aplanarities of the decay products

Abstract The production of τ pairs at the Z peak leads to interesting dynamical information contained in their spin density matrix. Besides the longitudinal polarization of each τ lepton, there are two independent spin-spin correlations associated with the transverse (within the production plane) and normal (to the production plane) polarization components. The transverse-normal spin correlation is both a parity-odd and time reversal-odd observable. We analyze the correlated angular distribution of the decay products as polarization analyzers of the τ + τ − system. We find two azimuthal asymmetries of the decay products and the incoming beam, which are able to disentangle these spin correlation observables without reconstructing the τ direction.

Leptogenesis with small violation of B−L

We analyze leptogenesis in the context of seesaw models with almost conserved lepton number, focusing on the L-conserving contribution to the flavoured CP asymmetries. We find that, contrary to previous claims, successful leptogenesis is feasible for masses of the lightest heavy neutrino as low as M1 ~ 106 GeV, without resorting to the resonant enhancement of the CP asymmetry for strongly degenerate heavy neutrinos. This lower limit renders thermal leptogenesis compatible with the gravitino bound in supersymmetric scenarios.

Tau polarization at the Z peak from the acollinearity between both τ-decay products

Abstract We discuss the possibility of measuring the τ -polarization distribution at the Z peak by studying the angular correlated distributions between the decay products of the τ-pairs. We give explicit formulae for the energy-energy correlation and for the acollinearity distribution of the decay products of the τ -pairs, for both the cross section and the forward-backward asymmetry, as a function of the τ -polarization and the Z-polarization. These distributions provide an independent method of measuring the τ -polarization, with a sensitivity comparable to the one that can be achieved by studying the energy spectrum of the produced pion in the decay τ → πν τ , and possibly better systematic errors. This new technique thus offers the prospect to achieve an increased precision in the determination of the electroweak mixing angle.

Leptogenesis in GeV-scale seesaw models

A bstractWe revisit the production of leptonic asymmetries in minimal extensions of the Standard Model that can explain neutrino masses, involving extra singlets with Majorana masses in the GeV scale. We study the quantum kinetic equations both analytically, via a perturbative expansion up to third order in the mixing angles, and numerically. The analytical solution allows us to identify the relevant CP invariants, and simplifies the exploration of the parameter space. We find that sizeable lepton asymmetries are compatible with non-degenerate neutrino masses and measurable active-sterile mixings.