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Register a new userRadiative Tau Decays with One Pseudoscalar Meson
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We have calculated the decay $tau rightarrow u pi(K) gamma$. We present the photon energy spectrum, the meson-photon invariant mass spectrum and the integrated rate as a function of a photon energy cut or an invariant mass cut. Both the internal bremsstrahlung and the structure dependent radiation have been taken into account. To this aim we have parametrized the form factors $F_V$ and $F_A$, which determine the structure dependent radiation. Observables especially suited for the measurement of the structure dependent form factors are found and implications on the width of the $a_1$ discussed.
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An observation of any lepton number violating process will undoubtedly point towards the existence of new physics and indirectly to the clear Majorana nature of the exchanged fermion. In this work, we explore the potential of a minimal extension of the Standard Model via heavy sterile fermions with masses in the $[ 0.1 - 10]$ GeV range concerning an extensive array of neutrinoless meson and tau decay processes. We assume that the Majorana neutrinos are produced on-shell, and focus on three-body decays. We conduct an update on the bounds on the active-sterile mixing elements, $|U_{ell_alpha 4} U_{ell_beta 4}|$, taking into account the most recent experimental bounds (and constraints) and new theoretical inputs, as well as the effects of a finite detector, imposing that the heavy neutrino decay within the detector. This allows to establish up-to-date comprehensive constraints on the sterile fermion parameter space. Our results suggest that the branching fractions of several decays are close to current sensitivities (likely within reach of future facilities), some being already in conflict with current data (as is the case of $K^+ to ell_alpha^+ ell_beta^+ pi^-$, and $tau^- to mu^+ pi^- pi^-$). We use these processes to extract constraints on all entries of an enlarged definition of a $3times 3$ effective Majorana neutrino mass matrix $m_{ u}^{alpha beta}$.
This article summarizes recent developments in $Bto D^{(ast)}tau u$ decays. We explain how to extract the tau leptons production properties from the kinematics of its decay products. The focus is on hadronic tau decays, which are most sensitive to the tau polarizations. We present new results for effects of new physics in tau polarization observables and quantify the observation prospects at BELLE II.
We study supersymmetric (SUSY) effects on $C_7(mu_b)$ and $C_7(mu_b)$ which are the Wilson coefficients (WCs) for $b to s gamma$ at b-quark mass scale $mu_b$ and are closely related to radiative $B$-meson decays. The SUSY-loop contributions to $C_7(mu_b)$ and $C_7(mu_b)$ are calculated at leading order (LO) in the Minimal Supersymmetric Standard Model (MSSM) with general quark-flavour violation (QFV). For the first time we perform a systematic MSSM parameter scan for the WCs $C_7(mu_b)$ and $C_7(mu_b)$ respecting all the relevant constraints, i.e. the theoretical constraints from vacuum stability conditions and the experimental constraints, such as those from $K$- and $B$-meson data and electroweak precision data, as well as recent limits on SUSY particle masses and the 125 GeV Higgs boson data from LHC experiments. From the parameter scan we find the following: (1) The MSSM contribution to Re($C_7(mu_b)$) can be as large as $sim pm 0.05$, which could correspond to about 3$sigma$ significance of New Physics (NP) signal in the future LHCb and Belle II experiments. (2) The MSSM contribution to Re($C_7(mu_b)$) can be as large as $sim -0.08$, which could correspond to about 4$sigma$ significance of NP signal in the future LHCb and Belle II experiments. (3) These large MSSM contributions to the WCs are mainly due to (i) large scharm-stop mixing and large scharm/stop involved trilinear couplings, (ii) large sstrange-sbottom mixing and large sstrange-sbottom involved trilinear couplings and (iii) large bottom Yukawa coupling $Y_b$ for large $tanbeta$ and large top Yukawa coupling $Y_t$. In case such large NP contributions to the WCs are really observed in the future experiments at Belle II and LHCb Upgrade, this could be the imprint of QFV SUSY (the MSSM with general QFV).
We revisit QCD calculations of radiative heavy meson decay form factors by including the subleading power corrections from the twist-two photon distribution amplitude at next-to-leading-order in $alpha_s$ with the method of the light-cone sum rules (LCSR). The desired hard-collinear factorization formula for the vacuum-to-photon correlation function with the interpolating currents for two heavy mesons is constructed with the operator-product-expansion technique in the presence of evanescent operators. Applying the background field approach, the higher twist corrections from both the two-particle and three-particle photon distribution amplitudes are further computed in the LCSR framework at leading-order in QCD, up to the twist-four accuracy. Combining the leading power point-like photon contribution at tree level and the subleading power resolved photon corrections from the newly derived LCSR, we update theory predictions for the nonperturbative couplings describing the electromagnetic decay processes of the heavy mesons $H^{ast , pm} to H^{pm} , gamma$, $H^{ast , 0} to H^{0} , gamma$, $H_s^{ast , pm} to H_s^{pm} , gamma$ (with $H=D, , B$). Furthermore, we perform an exploratory comparisons of our sum rule computations of the heavy-meson magnetic couplings with the previous determinations based upon different QCD approaches and phenomenological models.
The branching fractions of radiative leptonic $tau$ decays $(tau to l u bar{ u} gamma$, $l=e,mu)$ were recently measured by the Babar collaboration with a relative error of about 3%. The measurement of the branching ratio $mathcal{B} (tau to e bar{ u} u gamma)$, for a minimum photon energy of 10 MeV in the $tau$ rest frame, differs from our recent SM prediction by 3.5 standard deviations, whereas our result agrees with Babars value for $mathcal{B} (tau to mu bar{ u} u gamma)$. Our predictions also agree with the measurement of $mathcal{B} (mu to e bar{ u} u gamma)$ by the MEG collaboration. We also report on a recent proposal to test the $tau$ dipole moments via precise measurements of radiative leptonic $tau$ decays at high-luminosity $B$ factories.
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