arXiv subjects

Chee Sheng Fong

Publications and source records attributed to Chee Sheng Fong.

60 records · Page 4Linked to original sources

arXiv2010

Supersymmetric Leptogenesis

We study leptogenesis in the supersymmetric standard model plus the seesaw. We identify important qualitative differences that characterize supersymmetric leptogenesis with respect to the non-supersymmetric case. The lepton number asymmetries in fermions and scalars do not equilibrate, and are related via a non-vanishing gaugino chemical potential. Due to the presence of new anomalous symmetries, electroweak sphalerons couple to winos and higgsinos, and QCD sphalerons couple to gluinos, thus modifying the corresponding chemical equilibrium conditions. A new constraint on particles chemical potentials corresponding to an exactly conserved $R$-charge, that also involves the number density asymmetry of the heavy sneutrinos, appears. These new ingredients determine the $3\times 4$ matrices that mix up the density asymmetries of the lepton flavours and of the heavy sneutrinos. We explain why in all temperature ranges the particle thermodynamic system is characterized by the same number of independent quantities. Numerical differences with respect to usual treatment remain at the ${\cal O}(1)$ level.

hep-ph↗

arXiv2010

CP Violation from Scatterings with Gauge Bosons in Leptogenesis

We present an explicit computation of the CP asymmetry in scattering processes involving the heavy right-handed neutrinos of the type I seesaw framework and the Standard Model gauge bosons. Compared to CP violation in two--body decays and in scatterings with top quarks there are new contributions at one loop in the form of new type of vertex corrections as well as of box diagrams. We show that their presence implies that, unlike the CP asymmetry in scatterings with top quarks, the CP asymmetry in scatterings with gauge bosons is different from the two-body decay asymmetry even for hierarchical right-handed neutrinos. This also holds for the L-conserving CP asymmetry in scatterings with U(1)$_Y$ gauge bosons.

hep-ph↗

arXiv2010

Flavour in Soft Leptogenesis

Successful Soft Leptogenesis (SL) requires a relatively low mass scale for the SU(2) singlet neutrinos of $10^5-10^8$ GeV. However, conventional SL (unflavoured) requires an unnaturally small soft supersymmetry(SUSY)-breaking bilinear $B \ll \mathcal{O}({\rm TeV})$ coupling for successful leptogenesis. On the other hand, in this regime, the interactions mediated by $τ$, $μ$ (and even $e$) charged lepton Yukawa interactions are in equilibrium, making the lepton number asymmetries and the washouts flavour dependent. Hence, it is crucial to take into account the flavour effects. Considering a general soft SUSY-breaking trilinear $A$ couplings, it is possible to enhance the efficiency up to $\mathcal{O}(1000)$ compared to the unflavoured case. With the enhanced efficiency, we can raise the $B$ up to TeV scale for successful leptogenesis. Taking into account the low energy constraints, we verify that the fast lepton flavour violation processes induced by the soft SUSY-breaking slepton masses would not destroy the enhancement.

hep-ph↗

arXiv2008

On Gaugino Contributions to Soft Leptogenesis

We study the contributions to CP violation in right-handed sneutrino decays induced by soft supersymmetry-breaking gaugino masses including flavour effects and paying special attention to the role of thermal corrections. Using a field-theoretical as well as a quantum mechanical approach we compute the CP asymmetries and we conclude that for all the soft-supersymmetry breaking sources of CP violation considered, an exact cancellation between the asymmetries produced in the fermionic and bosonic channels occurs at T=0 up to second order in soft supersymmetry-breaking parameters. Once thermal effects are included the new sources of CP violation induced by supersymmetry-breaking gaugino masses can be sizeable and they can produce the observed baryon asymmetry for conventional values of the B parameter.

hep-ph↗

arXiv2008

On Quantum Effects in Soft Leptogenesis

It has been recently shown that quantum Boltzman equations may be relevant for leptogenesis. Quantum effects, which lead to a time-dependent CP asymmetry, have been shown to be particularly important for resonant leptogenesis when the asymmetry is generated by the decay of two nearly degenerate states. In this work we investigate the impact of the use of quantum Boltzman equations in the framework ``soft leptogenesis'' in which supersymmetry soft-breaking terms give a small mass splitting between the CP-even and CP-odd right-handed sneutrino states of a single generation and provide the CP-violating phase to generate the lepton asymmetry.

hep-ph↗

arXiv2008

Flavoured Soft Leptogenesis

We study the impact of flavour in ``soft leptogenesis'' (leptogenesis induced by soft supersymmetry breaking terms). We address the question of how flavour effects can affect the region of parameters in which successful soft leptogenesis induced by CP violation in the right-handed sneutrino mixing is possible. We find that for decays which occur in the intermediate to strong washout regimes for all flavours, the produced total $B-L$ asymmetry can be up to a factor ${\cal O}(30)$ larger than the one predicted with flavour effects being neglected. This enhancement, permits slightly larger values of the required lepton violating soft bilinear term.

hep-ph↗