We extend the Standard Model by adding two gauge-singlet Z 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 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 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 XENON1T experiment. PACS numbers: 95.35.+d; 11.30.Qc.

We present the extension of the Wakimoto construction to the Uq( su (2)k) quantum current algebra and its associated Zk quantum parafermion algebra. This construction is achieved in terms of various deformations of three classical free boson fields. We also give the vertex operators corresponding to the quantum spin-j representation.

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.Comment: 26 pages, Te

We calculate the damping rate γ l for longitudinal gluons with zero momentum in finite high temperature QCD and show that some of its contributing terms are infrared divergent. This is in contrast with the expectation that this damping rate is to be equal to the corresponding one γ t for transverse gluons which is known to be finite. Our calculation was motivated by the fact that similar divergent terms occur when we calculated in a previous work γ t to order p 2 , p being the momentum of the gluon. After we present our results, we briefly discuss them.

We calculate γ l (0), the damping rate for longitudinal on-shell gluons with zero momentum in hot QCD using the hard-thermal-loop (htl) scheme. We find it to be divergent in the infrared, which means that in this scheme γ l (0) is different from γ t (0), the corresponding damping rate for transverse gluons which is known to be finite. This result suggests that the htl scheme is infrared sensitive and thus may need to be improved upon in this sector. We discuss this issue after we present our calculation. pacs: 11.10.Wx 12.38.-t 12.38.Bx 12.38.Mh keywords: hard thermal loops. soft gluon damping. ENSK-TP-10Besides their importance regarding the stability of the quark-gluon plasma, gluon damping rates have been crucial in better understanding QCD at high temperature T . In early works, it has been noticed that in this regime, the determination of the dispersion laws for quarks and gluons beyond lowest order using standard perturbation theory is gaugedependent [1]. This problem has been emphasized in further works in which the gluon damping rates have been calculated to one-loop order in various gauges and schemes and different results have been obtained [2]. It was then realized that the problem was related to the way the expansion in powers of g, the perturbative QCD coupling constant, was performed: at high T (the hard scale), when the external momenta are soft, i.e., of magnitude gT, the standard loop expansion is not anymore an expansion in powers of g [3]. It was subsequently developed an effective perturbative expansion in the framework of a resummation scheme of the so-called hard thermal loops (htl) [4]. Using this scheme, the transverse-gluon damping rate γ t (0) with zero momentum was shown to be Coulomb-and-covariant-gaugeinvariant and determined in the strict Coulomb gauge to be finite and positive [5]. Later, a