Λb→Λcτνˉτ\Lambda_b\to\Lambda_c\tau\bar\nu_\tau decay in scalar and vector leptoquark scenarios

It has been shown that the anomalies observed in $\bar B\to D^{(\ast)}\tau\bar\nu_\tau$ and $\bar B\to \bar K\ell^+\ell^-$ decays can be resolved by adding a single scalar or vector leptoquark to the Standard Model, while constraints from other precision measurements in the flavour sector can be satisfied without fine-tuning. To further explore these two interesting scenarios, in this paper, we study their effects in the semi-leptonic $\Lambda_b\to\Lambda_c\tau\bar\nu_\tau$ decay. Using the best-fit solutions for the operator coefficients allowed by the current data of mesonic decays, we find that (i) the two scenarios give similar amounts of enhancements to the branching fraction $\mathcal B(\Lambda_b\to\Lambda_c\tau\bar\nu_\tau)$ and the ratio $R_{\Lambda_c}=\mathcal B(\Lambda_b\to\Lambda_c \tau\bar\nu_\tau)/\mathcal B(\Lambda_b\to\Lambda_c\ell\bar\nu_\ell)$, (ii) the two best-fit solutions in each of these two scenarios are also indistinguishable from each other, (iii) both scenarios give nearly the same predictions as those of the Standard Model for the longitudinal polarizations of $\Lambda_c$ and $\tau$ as well as the lepton-side forward-backward asymmetry. With future measurements of these observables in $\Lambda_b\to\Lambda_c\tau\bar\nu_\tau$ decay at the LHCb, the two leptoquark scenarios could be further tested, and even differentiated from the other NP explanations for the $R_{D^{(\ast)}}$ anomalies. We also discuss the feasibility for the measurements of these observables at the LHC and the future $e^+e^-$ colliders.Comment: 29 pages, 4 tables and 2 figures; More references and the feasibility for the measurements of the observables in these decays at the LHC and the future $e^+e^-$ colliders added, final version published in the journa

Freeze-in Dirac neutrinogenesis: thermal leptonic CP asymmetry

We present a freeze-in realization of the Dirac neutrinogenesis in which the decaying particle that generates the lepton-number asymmetry is in thermal equilibrium. As the right-handed Dirac neutrinos are produced non-thermally, the lepton-number asymmetry is accumulated and partially converted to the baryon-number asymmetry via the rapid sphaleron transitions. The necessary CP-violating condition can be fulfilled by a purely thermal kinetic phase from the wavefunction correction in the lepton-doublet sector, which has been neglected in most leptogenesis-based setup. Furthermore, this condition necessitates a preferred flavor basis in which both the charged-lepton and neutrino Yukawa matrices are non-diagonal. To protect such a proper Yukawa structure from the basis transformations in flavor space prior to the electroweak gauge symmetry breaking, we can resort to a plethora of model buildings aimed at deciphering the non-trivial Yukawa structures. Interestingly, based on the well-known tri-bimaximal mixing with a minimal correction from the charged-lepton or neutrino sector, we find that a simultaneous explanation of the baryon-number asymmetry in the Universe and the low-energy neutrino oscillation observables can be attributed to the mixing angle and the CP-violating phase introduced in the minimal correction.Comment: 28 pages and 7 figures; more discussions and one figure added, final version published in the journa

Revisiting B\to\pi K, \pi K^{\ast} and \rho K decays: CP violations and implication for New Physics

Combining the up-to-date experimental information on $B\to\pi K, \pi K^{\ast}$ and $\rho K$ decays, we revisit the decay rates and CP asymmetries of these decays within the framework of QCD factorization. Using an infrared finite gluon propagator of Cornwall prescription, we find that the time-like annihilation amplitude could contribute a large strong phase, while the space-like hard spectator scattering amplitude is real. Numerically, we find that all the branching ratios and most of the direct CP violations, except $A_{CP}(B^{\pm}\to K^{\pm}\pi^{0})$, agree with the current experimental data with an effective gluon mass $m_g\simeq0.5 {\rm GeV}$. Taking the unmatched difference in direct CP violations between $B\to\pi^{0} K^{\pm}$ and $\pi^{\mp}K^{\pm}$ decays as a hint of new physics, we perform a model-independent analysis of new physics contributions with a set of $\bar{s}(1+\gamma_{5})b\otimes\bar{q}(1+\gamma_{5})q$ (q=u,d) operators. Detail analyses of the relative impacts of the operators are presented in five cases. Fitting the twelve decay modes, parameter spaces are found generally with nontrivial weak phases. Our results may indicate that both strong phase from annihilation amplitude and new weak phase from new physics are needed to resolve the $\pi K$ puzzle. To further test the new physics hypothesis, the mixing-induced CP violations in $B\to\pi^{0}K_{S}$ and $\rho^{0}K_{S}$ are discussed and good agreements with the recent experimental data are found.Comment: Version published in JHE

The effects of massive graviton on the equilibrium between the black hole and radiation gas in an isolated box

It is well known that the black hole can has temperature and radiate the particles with black body spectrum, i.e. Hawking radiation. Therefore, if the black hole is surrounded by an isolated box, there is a thermal equilibrium between the black hole and radiation gas. A simple case considering the thermal equilibrium between the Schwarzschild black hole and radiation gas in an isolated box has been well investigated previously in detail, i.e. taking the conservation of energy and principle of maximal entropy for the isolated system into account. In this paper, following the above spirit, the effects of massive graviton on the thermal equilibrium will be investigated. For the gravity with massive graviton, we will use the de Rham-Gabadadze-Tolley (dRGT) massive gravity which has been proven to be ghost free. Because the graviton mass depends on two parameters in the dRGT massive gravity, here we just investigate two simple cases related to the two parameters, respectively. Our results show that in the first case the massive graviton can suppress or increase the condensation of black hole in the radiation gas although the $T-E$ diagram is similar like the Schwarzschild black hole case. For the second case, a new $T-E$ diagram has been obtained. Moreover, an interesting and important prediction is that the condensation of black hole just increases from the zero radius of horizon in this case, which is very different from the Schwarzschild black hole case.Comment: 9 pages, 4 figure

Generalized Vaidya Solutions and Misner-Sharp mass for nn-dimensional massive gravity

Dynamical solutions are always of interest to people in gravity theories. We derive a series of generalized Vaidya solutions in the $n$-dimensional de Rham-Gabadadze-Tolley (dRGT) massive gravity with a singular reference metric. Similar to the case of the Einstein gravity, the generalized Vaidya solution can describe shining/absorbing stars. Moreover, we also find a more general Vaidya-like solution by introducing a more generic matter field than the pure radiation in the original Vaidya spacetime. As a result, the above generalized Vaidya solution is naturally included in this Vaidya-like solution as a special case. We investigate the thermodynamics for this Vaidya-like spacetime by using the unified first law, and present the generalized Misner-Sharp mass. Our results show that the generalized Minser-Sharp mass does exist in this spacetime. In addition, the usual Clausius relation $\delta Q= TdS$ holds on the apparent horizon, which implicates that the massive gravity is in a thermodynamic equilibrium state. We find that the work density vanishes for the generalized Vaidya solution, while it appears in the more general Vaidya-like solution. Furthermore, the covariant generalized Minser-Sharp mass in the $n$-dimensional de Rham-Gabadadze-Tolley massive gravity is also derived by taking a general metric ansatz into account.Comment: 10 pages, no figure, version published in PR