18139806
MULTIBODY NEUTRINO EXCHANGE IN A NEUTRON STAR : NEUTRINO SEA AND BORDER EFFECTS
Abstract The interaction due to the exchange of massless neutrinos between neutrons is a long-range force. Border effects on this multibody exchange inside a dense core are studied and computed analytically in 1 + 1 dimensions. We demonstrate in this work that a proper treatment of the star's border effect automatically incorporates the condensate contribution as a consequence of the appropriate boundary conditions for the neutrino Feynman propagator inside the star. The total multibody exchange contribution is infrared-safe and vanishes exactly in 1 + 1 dimensions. The general conclusion of this work is that the border effect does not modify the result that neutrino exchange is infrared-safe. This toy model prepares the ground and gives the tools for the study of the realistic 3 + 1 star.
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.
67797503
First lattice QCD estimate of the g(D* D pi) coupling
We present the results of the first lattice QCD study of the strong coupling gDDπ. From our simulations in the quenched approximation, we obtain gDDπ = 18.8 ± 2.3 +1.1 −2.0 and bc = 0.67 ±0.08 +0.04 −0.06 . Whereas previous theoretical studies gave different predictions, our result favours a large value for bc. It agrees very well with the recent experimental value by CLEO. ˆ varies very little with the heavy mass and we find in the infinite mass limit b∞ = 0.69(18).
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.
16930940
Study of flavour dependences in leptogenesis
We study the impact of flavours on the efficiency factors and give analytical and numerical results of the baryon asymmetry taking into account the different charged lepton Yukawa contributions and the complete (diagonal and off-diagonal) L to B−L conversion A matrix. With this treatment we update the lower bound on the lightest right-handed neutrino mass.
118582901
Probing the supersymmetric type III seesaw: LFV at low-energies and at the LHC
We consider a supersymmetric type III seesaw, where the additional heavy states are embedded into complete SU(5) representations to preserve gauge coupling unification. Complying with phenomenological and experimental constraints strongly tightens the viable parameter space of the model. In particular, one expects very characteristic signals of lepton flavour violation both at low-energies and at the LHC, which offer the possibility of falsifying the model.
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
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.
119499960
Infrared Behavior of High-Temperature QCD
The damping rate \gamma_t(p) of on-shell transverse gluons with ultrasoft momentum p is calculated in the context of next-to-leading-order hard-thermal-loop-summed perturbation of high-temperature QCD. It is obtained in an expansion to second order in p. The first coefficient is recovered but that of order p^2 is found divergent in the infrared. Divergences from light-like momenta do also occur but are circumvented. Our result and method are critically discussed, particularly regarding a Ward identity obtained in the literature. When enforcing the equality between \gamma_t(0) and \gamma_l(0), a rough estimate of the magnetic mass is obtained. Carrying a similar calculation in the context of scalar quantum electrodynamics shows that the early ultrasoft-momentum expansion we make has little to do with the infrared sensitivity of the result.
15732602
Infrared Sensitivity in Damping Rate for Very Soft Moving Fermions in Finite Temperature QED
We calculate the fermion damping rate to second order in powers of the external momentum $p$ in the context of QED at finite temperature using the hard-thermal-loop (HTL) summation scheme. We find that the coefficient of order $p^{2}$ is divergent in the infrared whereas the two others are finite. This result suggests that the htl-based pertubation is infrared sensitive at next-to-leading order.
16544882
Damping of very soft moving quarks in high-temperature QCD
Abstract. We determine the analytic expression of the damping rates for very soft moving quarks in an expansion to second order in powers of their momentum in the context of QCD at high temperature. The calculation is performed using the hard-thermal-loop-summed perturbation scheme. We describe the range of validity of the expansion and make a comparison with other calculations, particularly those using a magnetic mass as a shield from infrared sensitivity. We discuss the possible occurrence of infrared divergences in our results and argue that they are due to magnetic sensitivity.