arXiv subjects

D. Comelli

Publications and source records attributed to D. Comelli.

43 records · Page 3Linked to original sources

arXiv1994

On the Spontaneous CP Breaking at Finite Temperature in a Nonminimal Supersymmetric Standard Model

We study the spontaneous CP breaking at finite temperature in the Higgs sector in the Minimal Supersymmetric Standard Model with a gauge singlet. We consider the contribution of the standard model particles and that of stops, charginos, neutralinos, charged and neutral Higgs boson to the one-loop effective potential. Plasma effects for all bosons are also included. Assuming CP conservation at zero temperature, so that experimental constraints coming from, {\it e.g.}, the electric dipole moment of the neutron are avoided, and the electroweak phase transition to be of the first order and proceeding via bubble nucleation, we show that spontaneous CP breaking cannot occur inside the bubble mainly due to large effects coming from the Higgs sector. However, spontaneous CP breaking can be present in the region of interest for the generation of the baryon asymmetry, namely inside the bubble wall. The important presence of very tiny explicit CP violating phases is also commented.

hep-ph↗

arXiv1994

Information and Discrimination from b Quark Production on Z Resonance

We introduce and define operatively in a model independent way a new ``heavy" b-vertexparameter, $η_b$, that can be derived from the measurement of a special polarization asymmetry for production of b-quarks on Z resonance. We show that the combination of the measurement of $η_b$ with that of a second and previously defined ``heavy" b-vertex parameter $δ_{bV}$ can discriminate a number of models of New Physics that remain associated to different ``trajectories" in the plane of the variations of the two parameters. This is shown in particular for some popular SUSY and technicolor-type models. In general, this discrimination is possible if a measurement of \underline{both} parameters is performed.

hep-ph↗

arXiv1993

Spontaneous Breaking of R parity in the Minimal Supersymmetric Standard Model Revisited

We reconsider the possibility of spontaneous breaking of $R$ parity in the Minimal Supersymmetric Standard Model. By a renormalization group analysis we find the parameter space in which a sneutrino gets a vacuum expectation value, leading to the spontaneous breaking of the lepton number and to the appearance of a phenomenologically unacceptable massless Goldstone boson. We then analyze the effect of operators giving rise to a tiny amount of explicit violation of lepton number, which could emerge as remnants of physics at some superheavy (Planck or GUT) scale in the low energy effective theory. We show that the conspiracy between the spontaneous and the explicit breaking scales can provide a mass to the Goldstone boson larger than the ${\rm Z}^0$ boson mass, hence allowing for a non vanishing sneutrino vacuum expectation value without increasing the invisible width of the ${\rm Z}^0$.

hep-ph↗

arXiv1993

Spontaneous CP Violation and Baryogenesis in the Minimal Supersymmetric Standard Model

We investigate the effects of the spontaneous CP violation at finite temperature in the Minimal Supersymmetric Standard Model on the baryogenesis at the weak scale. After a brief discussion of the case in which the electroweak phase transition is of the second order, we study in details the baryogenesis scenario when the transition proceeds via bubble nucleation. We show that the space-time dependent phase for the Higgs vacuum expectation values coming from the spontaneous CP violation can give rise to a efficient generation of baryon number inside the bubble walls if the superpotential parameters and the soft supersymmetry breaking ones are complex. However we find that in order to get the observed value for the baryon asymmetry of the universe the phases of such parameters can be as small as $10^{-5}$, giving rise to an electron dipole moment of the neutron well below the current experimental limit. Moreover a light Higgs pseudoscalar is needed, and an upper bound on its mass is obtained.

hep-ph↗

arXiv1993

One Loop Corrections To The Lightest Higgs Mass In The Minimal $η$ Model

We have evaluated the one loop correction to the bound on the lightest Higgs mass valid in the minimal, $ E_{6}$ based, supersymmetric $ η$ model. Under the assumption that the theory remains perturbative up to the $10^{16}$ GeV scale, we derive a conservative bound that decreases with the top mass for $M_t \leq 2 M_W$ and varies from $ \sim 160$ GeV to $\sim 145$ GeV when $90 \leq M_t \leq 200$ GeV.

hep-ph↗

arXiv1993

Spontaneous CP Violation in the Minimal Supersymmetric Standard Model at Finite Temperature

We show that in the Minimal Supersymmetric Standard Model one--loop effects at finite temperature may lead to a spontaneous breaking of CP invariance in the scalar sector. Requiring that the breaking takes place at the critical temperature for the electroweak phase transition, we find that the parameters space is compatible with a mass of the Higgs pseudoscalar in agreement with the present experimental lower bounds. Possible implications for baryogenesis are discussed.

hep-ph↗

arXiv1992

Radiatively Corrected Bound on the Light Higgs Mass in a Minimal Non Minimal Supersymmetric Standard Model

The neutral Higgs sector of the Minimal non Minimal Supersymmetric Standard Model is considered. By effective potential and R.G.E. supported method; an upper bound of the lightest Higgs is analysed. From the request of perturbativity of the coupling in the superpotential, adding the leading stop top contributions, the absolute bound of $\sim 130$ GeV for $90 GeV < m_t< 180 GeV$ and $M_{\tilde{t}} \simeq 1000 $ GeV is derived. The interesting dependence on $m_t$ for $\tanβ \to 1$ is discussed .

hep-ph↗