We study minimal scenarios of resonant leptogenesis near the electroweak phase transition. These models offer a number of testable phenomenological signatures for low-energy experiments and future high-energy colliders. Our study extends previous analyses of the relevant network of Boltzmann equations, consistently taking into account effects from out of equilibrium sphalerons and single lepton flavors. We show that the effects from single lepton flavors become very important in variants of resonant leptogenesis, where the observed baryon asymmetry in the Universe is created by lepton-to-baryon conversion of an individual lepton number, for example, that of the {tau}-lepton. The predictions of such resonant {tau}-leptogenesis models for the final baryon asymmetry are almost independent of the initial lepton-number and heavy neutrino abundances. These models accommodate the current neutrino data and have a number of testable phenomenological implications. They contain electroweak-scale heavy Majorana neutrinos with appreciable couplings to electrons and muons, which can be probed at future e{sup +}e{sup -} and {mu}{sup +}{mu}{sup -} high-energy colliders. In particular, resonant {tau}-leptogenesis models predict sizable 0{nu}{beta}{beta} decay, as well as e- and {mu}-number-violating processes, such as {mu}{yields}e{gamma} and {mu}{yields}e conversion in nuclei, with rates that are within reach of the experiments proposed by the MEG and MECOmore » collaborations.« less

Electroweak-scale resonant leptogenesis

We perform a comprehensive study of a number of rare charm decays, incorporating the first evaluation of the QCD corrections to the short distance contributions, as well as examining the long range effects. For processes mediated by the c → ul + l − transitions, we show that sensitivity to short distance physics exists in kinematic regions away from the vector meson resonances that dominate the total rate. In particular, we find that D → πl + l − and D → ρl + l − are sensitive to non-universal soft-breaking effects in the Minimal Supersymmetric Standard Model with R-parity conservation. We separately study the sensitivity of these modes to R-parity violating effects and derive new bounds on R-parity violating couplings. We also obtain predictions for these decays within extensions of the Standard Model, including extensions of the Higgs, gauge and fermion sectors, as well as models of dynamical electroweak symmetry breaking.

/pdf/rare-charm-decays-in-the-standard-model-and-beyond-yuilaghlk2.pdf

Rare Charm Decays in the Standard Model and Beyond

Low energy neutrinoless lepton flavor violating (LFV) processes are studied in an extension of the Standard Model (SM) by heavy SU(2)xU(1) singlet Dirac neutrinos. An upper bound procedure is elaborated for the evaluation of amplitudes. A comment on the extraction of heavy neutrino mixings from astrophysical observations is given. For processes not treated in the applied model the formalism not treated in the applied model the formalism for evaluating the branching ratios (BRs) is presented. The processes previously studied in the model are carefully examined. Some of the previous results are improved. Special attention is paid to the structure of the amplitudes and BRs as well as to the relations between BRs of different LFV processes. Numerical analysis of the BRs is done. The decoupling of heavy neutrinos is discussed and it is explicitely shown that the very heavy neutrinos decouple when the upper bound procedure is applied. The upper limits of the BRs are compared with the current experimental upper bounds and the processes interesting for the search for LFV are proposed. The LFV decays are shown to be unsuitable for finding upper bounds on "diagonal" LFV parameters. The B-meson LFV processes are suggested for the search of LFV in future B-factories.

Lepton flavor violation in the standard model extended by heavy singlet Dirac neutrinos

We analyze the cosmological implications of F-term hybrid inflation with a subdominant Fayet– Iliopoulos D-term whose presence explicitly breaks a D-parity in the inflaton-waterfall sector. This scenario of inflation, which is called FD-term hybrid model for brevity, can naturally predict lepton number violation at the electroweak scale, by tying the µ-parameter of the MSSM to an SO(3)-symmetric Majorana mass mN, via the vacuum expectation value of the inflaton field. We show how a negative Hubble-induced mass term in a next-to-minimal extension of supergravity helps to accommodate the present CMB data and considerably weaken the strict constraints on the theoretical parameters, resulting from cosmic string effects on the power spectrum PR. The usual gravitino overabundance constraint may be significantly relaxed in this model, once the enormous entropy release from the late decays of the ultraheavy waterfall gauge particles is properly considered. As the Universe enters a second thermalization phase involving a very low reheat temperature, which might be as low as about 0.3 TeV, thermal electroweak-scale resonant leptogenesis provides a viable mechanism for successful baryogenesis, while thermal righthanded sneutrinos emerge as new possible candidates for solving the cold dark matter problem. In addition, we discuss grand unified theory realizations of FD-term hybrid inflation devoid of cosmic strings and monopoles, based on the complete breaking of an SU(2)X subgroup. The FD-term hybrid model offers rich particle-physics phenomenology, which could be probed at highenergy colliders, as well as in low-energy experiments of lepton flavour or number violation.

/pdf/anatomy-of-f-d-term-hybrid-inflation-ymducq8i2r.pdf

Anatomy of F D -term hybrid inflation

Despite many tests, even the Minimal Manifest Left-Right Symmetric Model (MLRSM) has never been ultimately confirmed or falsified. LHC gives a new possibility to test directly the most conservative version of left-right symmetric models at so far not reachable energy scales. If we take into account precise limits on the model which come from low energy processes, like the muon decay, possible LHC signals are strongly limited through the correlations of parameters among heavy neutrinos, heavy gauge bosons and heavy Higgs particles. To illustrate the situation in the context of LHC, we consider the “golden” process pp → e
 +
 N . For instance, in a case of degenerate heavy neutrinos and heavy Higgs masses at 15 TeV (in agreement with FCNC bounds) we get σ(pp → e
 +
 N ) > 10 fb at $$ \sqrt {s} = 14\,{\text{TeV}} $$
 which is consistent with muon decay data for a very limited W
 2 masses in the range (3008 GeV, 3040 GeV). Without restrictions coming from the muon data, W
 2 masses would be in the range (1.0 TeV, 3.5 TeV). Influence of heavy Higgs particles themselves on the considered LHC process is negligible (the same is true for the light, SM neutral Higgs scalar analog). In the paper decay modes of the right-handed heavy gauge bosons and heavy neutrinos are also discussed. Both scenarios with typical see-saw light heavy neutrino mixings and the mixings which are independent of heavy neutrino masses are considered. In the second case heavy neutrino decays to the heavy charged gauge bosons not necessarily dominate over decay modes which include only light, SM-like particles.

/pdf/left-right-symmetry-at-lhc-and-precise-1-loop-low-energy-32axxx0t9t.pdf

Left-right symmetry at LHC and precise 1-loop low energy data

Gauge-independent analysis of KL → eμ in left-right models

The lepton-flavour-violating decay K_L --> e \mu is studied in detail within the context of SU(2)_R x SU(2)_L x U(1)_(B-L) models, which include heavy Majorana neutrinos. Particular attention is paid to the gauge independence of this decay process to one loop. In analogy with earlier studies on the K^0\bar{K}^0 mixing, it is explicitly shown how restoration of gauge invariance occurs in the decay amplitude containing the box diagrams, when the relevant Higgs-dependent self-energy and vertex graphs are taken into account in the on-shell skeleton renormalization scheme. Based on the analytic expressions so derived, we find that the branching ratio B(K_L --> e \mu) can be considerably enhanced due to the presence of left- and right-handed currents in the loop, and can reach values close to or even larger than the present experimental limit 3.3 x 10^{-11} in the manifest left-right symmetric model. Constraints on the parameter space of typical left-right models are derived from the possible decay K_L --> e \mu and a global analysis of other low-energy data.

Gauge-Independent Analysis of K_L --> e \mu in Left-Right Models

Heavy-neutrino chirality enhancement of the decay KL → eμ in left-right symmetric models

We study the decay $K_L -> e\mu$ in minimal extensions of the Standard Model based on the gauge groups $SU(2)_L x U(1)_Y$ and $SU(2)_R x SU(2)_L x U(1)_{B-L}$, in which heavy Majorana neutrinos are present. In $SU(2)_L x U(1)_Y$ models with chiral neutral singlets, $B(K_L -> e\mu )$ cannot be much larger than $5 x 10^{-15}$ without violating other low-energy constraints. In $SU(2)_L x SU(2)_R x U(1)_{B-L}$ models, we find that heavy-neutrino-chirality enhancements due to the presence of left-handed and right- handed currents can give rise to a branching ratio close to the present experimental limit $B(K_L -> e \mu)< 3.3 x 10^{-11}$.

Z. Gagyi-Palffy

Papers

Gauge-independent analysis of KL → eμ in left-right models

Gauge-Independent Analysis of K_L --> e \mu in Left-Right Models

Heavy-neutrino chirality enhancement of the decay KL → eμ in left-right symmetric models

Heavy-Neutrino Chirality Enhancement of the Decay $K_L -> e\mu $ in Left-Right Symmetric Models