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.
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.
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.
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.
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].
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.
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.
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.
120280840
FOUR-SPINON CONTRIBUTION TO THE DYNAMIC STRUCTURE FACTOR IN THE ANTIFERROMAGNETIC HEISENBERG MODEL
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.
117868341
Renormalization group equations of a cold dark matter two-singlet model
We study via the renormalization group equations at one-loop order the perturbativity and vacuum stability of a two-singlet model of cold dark matter (DM) that consists in extending the Standard Model with two real gauge-singlet scalar fields. We then investigate the regions in the parameter space in which the model is viable. For this, we require the model to reproduce the observed DM relic density abundance, to comply with the measured XENON 100 direct-detection upper bounds, and to be consistent with the renormalization group equation perturbativity and vacuum stability criteria up to 40 TeV. For a small mixing angle $\ensuremath{\theta}$ between the physical Higgs $h$ and auxiliary field, and DM-$h$ mutual coupling constant ${\ensuremath{\lambda}}_{0}^{(4)}$, we find that the auxiliary field mass is confined to the interval 116\char21{}138 GeV, while the DM mass is mainly confined to the region above 57 GeV. Increasing $\ensuremath{\theta}$ enriches the existing viability regions without relocating them, while increasing ${\ensuremath{\lambda}}_{0}^{(4)}$ shrinks them with a tiny relocation. We show that the model is consistent with the recent Higgs-boson-like discovery by the ATLAS and CMS experiments, while very light dark matter (masses below 5 GeV) is ruled out by the same experiments.