Weak decays of unstable bb-mesons

We investigate the decays of the excited $(b\bar q)$ mesons as probes of the short-distance structure of the weak $\Delta B=1$ transitions. These states are unstable under the electromagnetic or strong interactions although their widths are typically suppressed by phase space. As compared to the pseudoscalar $B$ meson, the purely leptonic decays of the vector $B^*$ are not chirally suppressed and are sensitive to different combinations of the underlying weak effective operators. An interesting example is $B^*_s\to \ell^+\ell^-$, which has a rate that can be accurately predicted in the standard model. The branching fraction is $\mathcal{B}\sim10^{-11}$, irrespective of the lepton flavor and where the main uncertainty stems from the unmeasured and theoretically not-well known $B_s^*$ width. We discuss the prospects for producing this decay mode at the LHC and explore the possibility of measuring the $B_s^*\to\ell\ell$ amplitude, instead, through scattering experiments at the $B_s^*$ resonance peak. Finally we also discuss the charged-current $B_{u,c}^*\to\ell\nu$ decay which can provide complementary information on the $b\to u\ell\nu$ and $b\to c\ell\nu$ transitions.Comment: 21 page

New Physics in s→uℓ−νˉs\to u\ell^-\bar\nu: Interplay between semileptonic kaon and hyperon decays

We review a novel model-independent approach to the analysis of new-physics effects in the $s\to u\ell^-\bar\nu$ transitions. We apply it to (semi)leptonic kaon decays and study their complementarity with pion and hyperon $\beta$ decays or with collider searches of new physics.Comment: Contribution to the NA62 Physics Handbook. It summarizes the analysis presented in arXiv:1605.07114 and discusses in more detail the interplay between $K_{\mu3}$ and semileptonic hyperon decays as new-physics probe

BB decay anomalies from nonabelian local horizontal symmetry

Recent anomalies in $B\to K^{(*)}\ell\ell$ meson decays are consistent with exchange of a heavy $Z'$ vector boson. Here we try to connect such new physics to understanding the origin of flavor, by gauging generation number. Phenomenological and theoretical considerations suggest that the smallest viable flavor symmetry (not including any extra U(1) factors) is chiral ${\rm SU(3)}_L\times{\rm SU(3)}_R$, which acts only on generation indices and does not distinguish between quarks and leptons. Spontaneous breaking of the symmetry gives rise to the standard model Yukawa matrices, and masses for the 16 $Z'$-like gauge bosons, one of which is presumed to be light enough to explain the $B\to K^{(*)}\ell\ell$ anomalies. We perform a bottom-up study of this framework, showing that it is highly constrained by LHC dilepton searches, meson mixing, $Z$ decays and CKM unitarity. Similar anomalies are predicted for semileptonic decays of $B$ to lighter mesons, with excesses in the $ee,\tau\tau$ channels and deficits in $\mu\mu$, but no deviation in $\nu\nu$. The lightest $Z'$ mass is $\lesssim 6\,$TeV if the gauge coupling is $\lesssim 1$.Comment: 13 pages, 4 figures; v2: minor corrections and improvements, references added; v3: corrected fig.1, published versio

Non-standard semileptonic hyperon decays

We investigate the discovery potential of semileptonic hyperon decays in terms of searches of new physics at teraelectronvolt scales. These decays are controlled by a small $SU(3)$-flavor breaking parameter that allows for systematic expansions and accurate predictions in terms of a reduced dependence on hadronic form factors. We find that muonic modes are very sensitive to non-standard scalar and tensor contributions and demonstrate that these could provide a powerful synergy with direct searches of new physics at the LHC.Comment: v2. Comparison with direct searches of new physics at the LHC presente

Revisiting the new-physics interpretation of the b→cτνb\to c\tau\nu data

We revisit the status of the new-physics interpretations of the anomalies in semileptonic $B$ decays in light of the new data reported by Belle on the lepton-universality ratios $R_{D^{(*)}}$ using the semileptonic tag and on the longitudinal polarization of the $D^*$ in $B\to D^*\tau\nu$, $F_L^{D^*}$. The preferred solutions involve new left-handed currents or tensor contributions. Interpretations with pure right-handed currents are disfavored by the LHC data, while pure scalar models are disfavored by the upper limits derived either from the LHC or from the $B_c$ lifetime. The observable $F_L^{D^*}$ also gives an important constraint leading to the exclusion of large regions of parameter space. Finally, we investigate the sensitivity of different observables to the various scenarios and conclude that a measurement of the tau polarization in the decay mode $B\to D\tau\nu$ would effectively discriminate among them.Comment: matches publised versio

Supernova constraints on dark flavored sectors

Proto-neutron stars forming a few seconds after core-collapse supernovae are hot and dense environments where hyperons can be efficiently produced by weak processes. By making use of various state-of-the-art supernova simulations combined with the proper extensions of the equations of state including Λ hyperons, we calculate the cooling of the star induced by the emission of dark particles X0 through the decay Λ → nX0. Comparing this novel energy-loss process to the neutrino cooling of SN 1987A allows us to set a stringent upper limit on the branching fraction, BR(Λ → nX0 ) ≤ 8 × 10−9, that we apply to massless dark photons and axions with flavor-violating couplings to quarks. We find that the new supernova bound can be orders of magnitude stronger than other limits in dark-sector models.publishedVersio

Confronting fuzzy dark matter with the rotation curves of nearby dwarf irregular galaxies

We investigate phenomenologically the viability of fuzzy dark matter (FDM). We do this by confronting the predictions of the model, in particular, the formation of a solitonic core at the center of dark matter halos, with a homogeneous and robust sample of high-resolution rotation curves from the ''LITTLE THINGS in 3D'' catalog. This comprises a collection of isolated, dark matter dominated dwarf-irregular galaxies that provides an optimal benchmark for cosmological studies. We use a statistical framework based on Markov chain Monte Carlo techniques that allows us to extract relevant parameters such as the axion mass, the mass of the solitonic core, the mass of the dark matter halo and its concentration parameter with a rather loose set of priors except for the implementation of a core-halo relation that is predicted by simulations. The results of the fits are used to perform various diagnostics on the predictions of the model. FDM provides an excellent fit to the rotation curves of the ''LITTLE THINGS in 3D'' catalog, with axion masses determined from different galaxies clustering around $m_a\approx2\times10^{-23}$ eV. However, we find two major problems in our analysis. First, the data follow scaling relations of the properties of the core which are not consistent with the predictions of the soliton. This problem is particularly acute in the core radius - mass relation with a tension that, at face value, has a significance $\gtrsim5\sigma$. The second problem is related to the strong suppression of the linear power spectrum that is predicted by FDM for the axion mass preferred by the data. This can be constrained very conservatively by the galaxy counts in our sample, which leads to a tension exceeding again $5\sigma$. We estimate the effects of baryons in our analysis and discuss whether they could alleviate the tensions of the model with observations.Comment: 22 pages, 9 figures, 3 table

The Mono-Tau Menace: From BB Decays to High-pTp_T Tails

We investigate the crossing-symmetry relation between $b\to c\tau^-\bar\nu$ decay and $b\bar c\to \tau^-\bar\nu$ scattering to derive direct correlations of New Physics in semi-tauonic $B$-meson decays and the mono-tau signature at the LHC ($pp\to\tau_h X$ + MET). Using an exhaustive set of effective operators and heavy mediators we find that the current ATLAS and CMS data constrain scenarios addressing anomalies in $B$-decays. Pure tensor solutions, completed by leptoquark, and right-handed solutions, completed by $W^\prime_R$ or leptoquark, are challenged by our analysis. Furthermore, the sensitivity that will be achieved in the high-luminosity phase of the LHC will probe $all$ the possible scenarios that explain the anomalies. Finally, we note that the LHC is also competitive in the $b\to u$ transitions and bounds in some cases are currently better than those from $B$ decays.Comment: No comment