Pairing effect on the giant dipole resonance width at low temperature

The width of the giant dipole resonance (GDR) at finite temperature T in Sn-120 is calculated within the Phonon Damping Model including the neutron thermal pairing gap determined from the modified BCS theory. It is shown that the effect of thermal pairing causes a smaller GDR width at T below 2 MeV as compared to the one obtained neglecting pairing. This improves significantly the agreement between theory and experiment including the most recent data point at T = 1 MeV.Comment: 8 pages, 5 figures to be published in Physical Review

The μ→eγ\mu\to e\gamma decay in an EW-scale non-sterile RH neutrino model

We study in this research the phenomenology of $\mu\to e\gamma$ decay in a scenario of the class of extended models with non-sterile right-handed (RH) neutrino at electroweak (EW) scale proposed by P.Q. Hung. Field content of the standard model (SM) is enlarged by introducing for each SM fermion a corresponding mirror partner with the same quantum numbers beside opposite chirality. Light neutrino masses are generated via the type-I see-saw mechanism and it is also proved to be relevant with low energy within the EW scale of the RH neutrino masses. We introduce the model and derive branching ratio of the $\mu\to e\gamma$ decay at one-loop approximation with the participation of W gauge boson, neutral and singly charged Higgs scalars. After that we set constraints on relevant parameters and predict the sensitivities of the decay channel under the present and future experiments.Comment: 19 pages, 8 figure

Muon anomalous magnetic dipole moment in a low scale type I see-saw model

Recent experimental results on muon anomalous magnetic dipole moment have shown a $4.2\sigma$ tension with the SM prediction, which has blown a fresh wind into the elementary particle physics community. The problem is believed to be explained only by physics beyond the standard model. Current work considers the anomalous moment in a scenario of models with mirror symmetry and type I see-saw mechanism at low energy scale of electroweak interactions. After a brief introduction to the model, a detailed numerical analysis of muon anomalous phenomenology will be carefully performed.Comment: 15 pages, 2 tables, 5 figue

Revisiting Minimal Lepton Flavour Violation in the Light of Leptonic CP Violation

The Minimal Lepton Flavour Violation (MLFV) framework is discussed after the recent indication for CP violation in the leptonic sector. Among the three distinct versions of MLFV, the one with degenerate right-handed neutrinos will be disfavoured, if this indication is confirmed. The predictions for leptonic radiative rare decays and muon conversion in nuclei are analysed, identifying strategies to disentangle the different MLFV scenarios. The claim that the present anomalies in the semi-leptonic $B$-meson decays can be explained within the MLFV context is critically re-examined concluding that such an explanation is not compatible with the present bounds from purely leptonic processes.Comment: 36 pages, 4 figures. V2: References added; version accepted for publication on JHE

Damping of giant dipole resonance in hot rotating nuclei

The phonon damping model (PDM) is extended to include the effect of angular momentum at finite temperature. The model is applied to the study of damping of giant dipole resonance (GDR) in hot and noncollectively rotating spherical nuclei. The numerical results obtained for Mo88 and Sn106 show that the GDR width increases with both temperature T and angular momentum M. At T > 4 MeV and M<= 60 hbar the increase in the GDR width slows down for Sn106, whereas at M<= 80 hbar the GDR widths in both nuclei nearly saturate. By adopting the nuclear shear viscosity extracted from fission data at T= 0, it is shown that the maximal value of the angular momentum for Mo88 and Sn106 should be around 46 and 55 hbar, respectively, so that the universal conjecture for the lower bound of the specific shear viscosity for all fluids is not violated up to T= 5 MeV.Comment: 19 pages, 6 figures, accepted in Phys. Rev.

Radiative Emission of Neutrino Pairs in Atoms and Light Sterile Neutrinos

The process of Radiative Emission of Neutrino Pair (RENP) in atoms is sensitive to the absolute neutrino mass scale, the type of spectrum neutrino masses obey and the nature - Dirac or Majorana - of massive neutrinos. We analyse the possibility to test the hypothesis of existence of neutrinos with masses at the eV scale coupled to the electron in the weak charged lepton current in an RENP experiment. The presence of eV scale neutrinos in the neutrino mixing is associated with the existence of sterile neutrinos which mix with the active flavour neutrinos. At present there are a number of hints for active-sterile neutrino oscillations driven by $\Delta m^2 \sim 1~{\rm eV^2}$. We perform a detailed analysis of the RENP phenomenology within the "3 + 1" scheme with one sterile neutrino.Comment: LATEX file, 19 pages, the effects of the 3-4 mixing taken into account, one table and four figures added, version to be published in Phys. Lett.

Specific shear viscosity in hot rotating systems of paired fermions

The specific shear viscosity $\bar\eta$ of a classically rotating system of nucleons that interact via a monopole pairing interaction is calculated including the effects of thermal fluctuations and coupling to pair vibrations within the selfconsistent quasiparticle random-phase approximation. It is found that $\bar\eta$ increases with angular momentum $M$ at a given temperature $T$. In medium and heavy systems, $\bar\eta$ decreases with increasing $T$ at $T\geq$ 2 MeV and this feature is not affected much by angular momentum. But in lighter systems (with the mass number $A\leq$ 20), $\bar\eta$ increases with $T$ at a value of $M$ close to the maximal value $M_{max}$, which is defined as the limiting angular momentum for each system. The values of $\bar\eta$ obtained within the schematic model as well as for systems with realistic single-particle energies are always larger than the universal lower-bound conjecture $\hbar/(4\pi k_B)$ up to $T$=5 MeV.Comment: 19 pages, 7 figures, accepted for publication in Phys. Rev.