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).
121461927
Cancellation of the neutron electric dipole moment in quark model calculations of Baluni's CP violating strong interaction
Abstract The neutron electric dipole moment (Dn) generated by strong CP violation is due to the anomaly plus non-perturbative U (1) effects. It should vanish in quark models, which do not incorporate these two ingredients. Calculations are presented showing how this necessary cancellation does occur in a Lorentz vector potential model, but not in a scalar potential or in a bag model; in the latter cases, it is argued that the non-zero result is a model artefact. In old perturbation theory, the cancellation when present occurs between pair and 1 2 − intermediate state contributions.
119389183
Decays of Heavy Mesons
We present preliminary results for heavy to light transitions of pseudoscalar mesons, induced by the vector and tensor operators. This lattice study is performed in quenched approximation, by using the nonperturbatively improved Wilson action and operators. We also update the values of the heavy-light meson decay constants.
17798531
Addendum to “Finite-size effects on multibody neutrino exchange”
The interaction energy of the neutrons due to massless neutrino exchange in a neutron star has recently been proved, using an eective theory, to be extremely small and infrared-safe. Our comment here is of conceptual order: two approaches to compute the total interaction energy density have recently been proposed. Here, we study the connection between these two approaches. From CP invariance, we argue that the resulting interaction energy has to be even in the parameter b = GFnn= p 2, which expresses the static neutrino potential created by a neutron medium of density nn.
38599601
Finite-size effects on multibody neutrino exchange
The effect of multibody massless neutrino exchanges between neutrons inside a finite-size neutron star is studied. We use an effective Lagrangian, which incorporates the effect of the neutrons on the neutrinos. Following Schwinger, it is shown that the total interaction energy density is computed by comparing the zero point energy of the neutrino sea with and without the star. It has already been shown that in an infinite-size star the total energy due to neutrino exchange vanishes exactly. The opposite claim that massless neutrino exchange would produce a huge energy is due to an improper summation of an infrared-divergent quantity. The same vanishing of the total energy has been proved exactly in the case of a finite star in a one-dimensional toy model. 
Here we study the three-dimensional case. We first consider the effect of a sharp star border, assumed to be a plane. We find that there is a non- vanishing of the zero point energy density difference between the inside and the outside due to the refraction index at the border and the consequent non-penetrating waves. An analytical and numerical calculation for the case of a spherical star with a sharp border confirms that the preceding border effect is the dominant one. The total result is shown to be infrared-safe, thus confirming that there is no need to assume a neutrino mass. The ultraviolet cut-offs, which correspond in some sense to the matching of the effective theory with the exact one, are discussed. Finally the energy due to long distance neutrino exchange is of the order of $10^{-8} -- 10^{-13} GeV per neutron$, i.e. negligible with respect to the neutron mass density.
118558016
Potential of a linear collider for lepton flavour violation studies in the susy seesaw
We study the potential of an e?e? Linear Collider for charged lepton flavour violation studies in a supersymmetric framework where neutrino masses and mixings are explained by a type-I seesaw. Focusing on e-? flavour transitions, we evaluate the background from standard model and supersymmetric charged currents to the e? + signal. We study the energy dependence of both signal and background, and the effect of beam polarisation in increasing the signal over background significance. Finally, we consider the ???? + final state in e?e? collisions that, despite being signal suppressed by requiring two e-? flavour transitions, is found to be a clear signature of charged lepton flavour violation due to a very reduced standard model background. This contribution summarises part of the work done in [1].
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.
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.
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.
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