Rarita-Schwinger-Weyl semimetal in Jeff=3/2 electron systems

We propose a relativistic Jeff=3/2 semimetal with 4d1 or 5d1 electrons on a cubic lattice when the strong spin-orbital coupling takes over the Hunds' coupling. A relativistic spinor with spin 3/2 is historically called Rarita-Schwinger spinor. In the massless case, the right- and left-handed chiral degrees of freedom of the Rarita-Schwinger spinors are independent. In the lattice model that we propose, the right- and left- handed gapless points in Brillouin zone are separated. We call this linearly dispersed semimetal Rarita-Schwinger-Weyl semimetal, similar to Weyl semimetal for spin 1/2 systems. There is a network of gapless Fermi arcs in the surface Brillouin zone if n1+n2+n3 is even for the normal vector (n1,n2,n3) of the surface while the surface is insulator if n1+n2+n3 is odd.Comment: 5 pages, 4 figure

Isospin-Violating Dark Matter and Neutrinos From the Sun

We study the indirect detection of dark matter through neutrino flux from their annihilation in the center of the Sun, in a class of theories where the dark matter-nucleon spin-independent interactions break the isospin symmetry. We point out that, while the direct detection bounds with heavy targets like Xenon are weakened and reconciled with the positive signals in DAMA and CoGeNT experiments, the indirect detection using neutrino telescopes can impose a relatively stronger constraint and brings tension to such explanation, if the annihilation is dominated by heavy quark or $\tau$-lepton final states. As a consequence, the qualified isospin violating dark matter candidate has to preferably annihilate into light flavors.Comment: 5 pages, 3 figures, 1 tabl

Rapidity resummation for BB-meson wave functions

Transverse-momentum dependent (TMD) hadronic wave functions develop light-cone divergences under QCD corrections, which are commonly regularized by the rapidity $\zeta$ of gauge vector defining the non-light-like Wilson lines. The yielding rapidity logarithms from infrared enhancement need to be resummed for both hadronic wave functions and short-distance functions, to achieve scheme-independent calculations of physical quantities. We briefly review the recent progress on the rapidity resummation for $B$-meson wave functions which are the key ingredients of TMD factorization formulae for radiative-leptonic, semi-leptonic and non-leptonic $B$-meson decays. The crucial observation is that rapidity resummation induces a strong suppression of $B$-meson wave functions at small light-quark momentum, strengthening the applicability of TMD factorization in exclusive $B$-meson decays. The phenomenological consequence of rapidity-resummation improved $B$-meson wave functions is further discussed in the context of $B \to \pi$ transition form factors at large hadronic recoil.Comment: 6 pages, 2 figures, Conference proceedings for the workshop of QCD@work, Giovinazzo (Italy), June 16-19, 201

QCD corrections to B→πB \to \pi form factors from light-cone sum rules

We compute perturbative corrections to $B \to \pi$ form factors from QCD light-cone sum rules with $B$-meson distribution amplitudes. Applying the method of regions we demonstrate factorization of the vacuum-to-$B$-meson correlation function defined with an interpolating current for pion, at one-loop level, explicitly in the heavy quark limit. The short-distance functions in the factorization formulae of the correlation function involves both hard and hard-collinear scales; and these functions can be further factorized into hard coefficients by integrating out the hard fluctuations and jet functions encoding the hard-collinear information. Resummation of large logarithms in the short-distance functions is then achieved via the standard renormalization-group approach. We further show that structures of the factorization formulae for $f_{B \pi}^{+}(q^2)$ and $f_{B \pi}^{0}(q^2)$ at large hadronic recoil from QCD light-cone sum rules match that derived in QCD factorization. In particular, we perform an exploratory phenomenological analysis of $B \to \pi$ form factors, paying attention to various sources of perturbative and systematic uncertainties, and extract $|V_{ub}|= \left(3.05^{+0.54}_{-0.38} |_{\rm th.} \pm 0.09 |_{\rm exp.}\right) \times 10^{-3}$ with the inverse moment of the $B$-meson distribution amplitude $\phi_B^{+}(\omega)$ determined by reproducing $f_{B \pi}^{+}(q^2=0)$ obtained from the light-cone sum rules with $\pi$ distribution amplitudes. Furthermore, we present the invariant-mass distributions of the lepton pair for $B \to \pi \ell \nu_{\ell}$ ($\ell= \mu \,, \tau$) in the whole kinematic region. Finally, we discuss non-valence Fock state contributions to the $B \to \pi$ form factors $f_{B \pi}^{+}(q^2)$ and $f_{B \pi}^{0}(q^2)$ in brief.Comment: 44 pages, 12 figure