118631967
A Two-Singlet Model for Light Cold Dark Matter
We extend the standard model by adding two gauge-singlet Z{sub 2}-symmetric scalar fields that interact with visible matter only through the Higgs particle. One is a stable dark matter WIMP, and the other one undergoes a spontaneous breaking of the symmetry that opens new channels for the dark matter annihilation, hence lowering the mass of the WIMP. We study the effects of the observed dark matter relic abundance on the WIMP annihilation cross section and find that in most regions of the parameters' space, light dark matter is viable. We also compare the elastic-scattering cross section of our dark matter candidate off a nucleus with existing (CDMSII and XENON100) and projected (SuperCDMS and XENON1T) experimental exclusion bounds. We find that most of the allowed mass range for light dark matter will be probed by the projected sensitivity of the XENON1T experiment.
54663418
Phenomenology of a light cold dark matter two-singlet model
We study the implications of phenomenological processes on a two-singlet extension of the Standard Model we introduced in a previous work to describe light cold dark matter. We look into
119344257
Infrared behavior of the dispersion relations in high-temperature scalar QED
We investigate the infrared properties of the next-to-leading-order dispersion relations in scalar quantum electrodynamics at high temperature in the context of hard-thermal-loop perturbation theory. Specifically, we determine the damping rate and the energy for scalars with ultrasoft momenta. We show by explicit calculations that an early external-momentum expansion, before the Matsubara sum is performed, gives exactly the same result as a late one. The damping rate is obtained up to fourth order included in the ultrasoft momentum and the energy up to second order. The damping rate is found sensitive in the infrared whereas the energy is not.
26502186
ULTRASOFT QUARK DAMPING IN HOT QCD
We determine the quark damping rates in the context of next-to-leading order hard-thermal-loop summed perturbation of high-temperature QCD where weak coupling is assumed. The quarks are ultrasoft. Three types of divergent behavior are encountered: infrared, light-cone and at specific points determined by the gluon energies. The infrared divergence persists and is logarithmic whereas the two others are circumvented.
8156739
Exact four-spinon dynamical correlation function of the Heisenberg model
Abstract In this paper we derive the exact expression of the four-spinon contribution to the dynamical correlation function of the spin S = 1 2 anisotropic (XXZ) Heisenberg model in the antiferromagnetic regime. We extensively study its isotropic (XXX) limit and derive perturbatively the Ising one. Our method relies on the quantum affine symmetry of the model, which allows for a systematic diagonalization of the Hamiltonian in the thermodynamic limit and for an exact calculation of matrix elements of local spin operators. In fact, we argue that the familiar criticism of this method related to the complication of these matrix elements is not justified. First, we give, in the form of contour integrals, an exact expression for the n-spinon contribution. After we compile recently found results concerning the two-spinon contribution, we specialize the n-spinon formula to the new case n = 4. Then we give an explicit series representation of this contribution in the isotropic limit. Finally, after we show that this representation is free of divergences, we discuss the Ising limit in which a simple expression is found up to first order in the anisotropy parameter.
118449799
Photon damping in one-loop HTL perturbation theory
A bstractWe determine the damping rates of slow-moving photons in next-to-leading order hard-thermal-loop perturbation of massless QED. We find both longitudinal and transverse rates finite, positive, and equal at zero momentum. Various divergences, light-cone and at specific momenta, but not infrared, appear and cancel systematically.
16383524
Preliminaries on a lattice analysis of the pion light-cone wave function: A partonic signal?
We present the first attempt of a new method to compute the pion light-cone wave function (LCWF) on the lattice. We compute the matrix element between the pion and the vacuum of a non-local operator: the propagator of a ``scalar quark'' (named for short "squark"). A theoretical analysis shows that for some kinematical conditions (energetic pion and hard squark) this matrix element depends dominantly on the LCWF $\Phi_\pi(u), u\in [0,1]$. On the lattice, the discretization of the parton momenta imposes further constraints on the pion momentum. The two-point Green functions made of squark-quark and squark-squark fields show hadron-like bound-state behaviour and verify the standard energy spectrum. We show some indications that during a short time, after being created, the system of the spectator quark and the squark behave like partons, before they form a hadron-like bound state. This short time is the place where the partonic wave function has to be looked for.
124762744
Heavy flavor meson decay constants with Wilson fermions at β = 6.4
We present an extensive lattice study of the physical properties of mesons, composed of a heavy, H, and a light, q, quark, at β = 6.4 on a 243 × 60 lattice, using the Wilson action in the quenched approximation. We have studied the mass spectrum and the decay constants of vector and pseudoscalar mesons. We find significant violations of the mass scaling law fP√MP = const. ( ∼ 50% for D-mesons and ∼ 20% for B-mesons). The results using quenched but propagating quarks are remarkably consistent with the static results when the scale is taken from the pion decay constant. Combining the results obtained by several calculations of the pseudoscalar decay constants as a function of the meson mass, at different values of the lattice spacing, we obtain by extrapolation fB√BB = (220 ± 40) MeV (fB = (205 ± 40) MeV and BB = 1.16 ± 0.07), where BB is the renormalization group invariant B-parameter relevant for Bd-Bd mixing. We also find fBs2BB,fBd2BBd = 1.19 ± 0.10. This last result is relevant in experimental studies of B3-B3 mixing. The vector-pseudoscalar mass splittings do not follow the predicted behaviour, MV2 - MP2 ∼ const., which is expected (and found experimentally) in the limit of large heavy quark masses (i.e. when mQ ⪢ ΛQCD).
6263787
Leptogenesis in SO(10) models with a left-right symmetric seesaw mechanism
We study leptogenesis in supersymmetric SO(10) models with a left-right symmetric seesaw mechanism, including flavour effects and the contribution of the next-to-lightest right-handed neutrino. Assuming M_D = M_u and hierarchical light neutrino masses, we find that successful leptogenesis is possible for 4 out of the 8 right-handed neutrino mass spectra that are compatible with the observed neutrino data. An accurate description of charged fermion masses appears to be an important ingredient in the analysis.
119111618
Flavour Violation in charged leptons: Present and Future
In the absence of a fundamental principle preventing charged lepton flavour violation, one expects that extensions of the Standard Model accommodating neutrino masses and mixings should also allow for charged lepton flavour violating processes such as li→ljγ, li→ljlklm and μ–e conversion in nuclei, for which the rates depend in general on the mechanism of neutrino mass generation. In addition to low-energy experiments, there are also searches for lepton flavour violation at colliders, where new physics can be directly probed through flavour violating production and/or decays of heavy states. In a model independent way, we briefly use effective operators responsible for these processes to derive information about the underlying framework of new physics. We then consider some specific classes of models (supersymmetry, extra dimensions, grand unified theories) that account for rich scenarios of charged lepton flavour violation. We also comment on the role of charged lepton flavour violation in disentangling between models of new physics.
119095917
Heavy to light vector meson semileptonic decays
New (preliminary) results for the form factors relevant for the semileptonic decays of heavy pseudoscalar to a light vector meson are presented. In particular, we discuss the form factors for D -->K* and B -->rho modes.