arXiv subjects

G. F. Giudice

Publications and source records attributed to G. F. Giudice.

61 records · Page 4Linked to original sources

arXiv1994

Supersymmetric corrections to $ε^\prime /εat the leading order in QCD and QED

We study the corrections to $ε^\prime /ε$ in the minimal supersymmetric model at the leading order in QCD and QED. Supersymmetry can increase the standard model prediction for $ε^\prime /ε$ by at most 40\% for $m_t=174$ GeV, an enhancement which is indistinguishable from the present theoretical uncertainties. The most conspicuous effect of supersymmetry is a strong depletion of $ε^\prime /ε$. For certain choices of supersymmetric parameters, vanishing and even small negative values of $ε^\prime /ε$ can be obtained for the top quark in the CDF range.

hep-lat↗

arXiv1994

Can EROS/MACHO be detecting the galactic spheroid instead of the galactic halo?

Models of our galaxy based on dynamical observations predict a spheroid component much heavier than accounted for by direct measurements of star counts and high velocity stars. If, as first suggested by Caldwell and Ostriker, this discrepancy is due to a large population of faint low-mass stars or dark objects in the spheroid, the spheroid could be responsible for microlensing events for sources in the Large Magellanic Cloud (LMC). We show that, although the rate of events is lower than predicted by a galactic halo made of microlensing objects, it is still significant for EROS/MACHO observations. Because of the different matter distributions in the halo and spheroid components, a comparison between microlensing event rates in the LMC, future measurements of microlensing in the galactic bulge and, possibly, in M31 can provide information about the amounts of dark objects in the different galactic components. If the EROS/MACHO collaborations find a deficiency with respect to their halo expectation, when more statistics are available, their detected events could be interpreted as coming from spheroid microlenses, allowing for a galactic halo composed entirely of non-baryonic dark matter.

astro-ph↗

arXiv1994

Is the halo responsible for the microlensing events?

We discuss whether the astrophysical objects responsible for the recently reported microlensing events of sources in the Large Magellanic Cloud can be identified as the brown dwarf components of the spheroid of our galaxy, rather than the constituents of a dark baryonic halo.

astro-ph↗

arXiv1993

Towards a Model-Independent Analysis of Rare $B$ Decays

Motivated by the experimental accessibility of rare $B$ decays in the ongoing and planned experiments, we propose to undertake a model-independent analysis of the inclusive decay rates and distributions in the processes \bgamaxs~ and \Bsell ~($B=B^\pm$ or $B^0_d$). We show how measurements of the decay rates and distributions in these processes would allow us to extract the magnitude and sign of the dominant Wilson coefficients of the magnetic moment operator $\mb \bar{s}_L σ_{μν} b_R F^{μν}$ and the four-fermion operators $(\bar{s}_L γ_μb_L)(\bar{\ell} γ^μ \ell)$ and $(\bar{s}_L γ_μb_L)(\bar{\ell} γ^μγ^5 \ell)$. Non-standard-model effects could thus manifest themselves at low energy in rare $B$ decays through the Wilson coefficient having values distinctly different from their standard-model counterparts. We illustrate this possibility using the examples of the two-doublet Higgs models and the minimal supersymmetric models. The dilepton invariant mass spectrum and the forward-backward asymmetry of $\ell^+$ in the centre-of-mass system of the dilepton pair in the decay \Bsell ~are also worked out for the standard model and some representative solutions for the other two models.

hep-ph↗

arXiv1993

Conditions on supersymmetry soft-breaking terms from GUTs

We study the effect of integrating out the heavy fields in a supersymmetric GUT which does not contain small mass parameters in the limit of exact supersymmetry. The trilinear ($A$) and bilinear ($B$) coefficients of the supersymmetry soft-breaking terms of the low-energy effective theory are related in a simple and model-independent way to those of the underlying theory. {}From these relations, we obtain the bound $|B|\ge 2$, which, together with the requirements of stability of the potential and electroweak symmetry breaking, imposes severe constraints on the space of allowed supersymmetric parameters. In models based on supergravity with a flat Kähler metric, we obtain $B=2$, instead of the relation $B=A-1$ usually used in phenomenological applications. The low-energy theory contains also a supersymmetric mass term $μ$ for the two Higgs doublets, which is of the order of the supersymmetry-breaking scale.

hep-ph↗

arXiv1993

$b \to s γ$ Decay and Supersymmetry

The inclusive radiative $B$-decay is a sensitive probe of new physics, especially if related to the virtual exchange of a charged Higgs boson. Supersymmetric models provide a particularly interesting example. In the limit of exact supersymmetry, BR($b \to sγ$)~=~0, due to the vanishing of any magnetic-moment transition operator. We illustrate the impact of this constraint for realistic values of the supersymmetry-breaking parameters.

hep-ph↗

arXiv1992

The Supersymmetric Singlet Majoron

We study the supersymmetrized version of the singlet majoron model and, performing an analysis of the renormalization group equation improved potential, we find that a spontaneous breaking of $R$-parity can be achieved for a wide range of the parameters. Studying the finite temperature effective potential, we show that the phase transition leading to $R$-parity breaking can be of the first order and can occur at temperatures below the weak scale, thus avoiding any constraint coming from the requirement of the preservation of the baryon asymmetry in the early Universe.

hep-ph↗