Joan Sola

Scaling behavior of the cosmological constant and the possible existence of new forces and new light degrees of freedom

Abstract A large value of the cosmological constant (CC) is induced in the Standard Model (SM) of Elementary Particle Physics because of Spontaneous Symmetry Breaking. To provide a small value of the observable CC one has to introduce the vacuum term which cancels the induced one at some point in the very far infrared cosmic scale. Starting from this point we investigate whether the cancellation is preserved at different energy scales. We find that the running of the Higgs mass, couplings and the vacuum term inevitably result in a scaling dependence of the observable value. As a consequence one meets a nonzero CC at an energy scale comparable to the typical electron neutrino mass suggested by some experiments, and the order of magnitude of this constant is roughly the one derived from recent supernovae observations. However the sign of it is negative – opposite to what is suggested by these observations. This discrepancy may be a hint of the existence of an extra very light scalar, perhaps a Cosmon-like dilaton, which should essentially decouple from the SM Lagrangian, but that it nevertheless could mediate new macroscopic forces in the submillimeter range.

FCNC top quark decays in the MSSM: a door to SUSY physics in high luminosity colliders?

We study the FCNC top quark decays t→ch in the framework of the MSSM, where h≡h0,H0,A0 is any of the supersymmetric neutral Higgs bosons. We include the leading set of SUSY-QCD and SUSY electroweak contributions. While the FCNC top quark decay into the SM Higgs boson has such a negligible rate that it will not be accessible to any presently conceivable accelerator, we find that there is a chance that the potential rates in the MSSM can be measured at the high luminosity colliders round the corner, especially at the LHC and possibly at a future LC, but we deem it difficult at the upgraded Tevatron. In view of the large SUSY-QCD effects that we find in the Higgs channels, and due to some discrepancies in the literature, we have revisited the FCNC top quark decay into gluon, t→cg, in our framework. We confirm that the possibility of sizeable rates does not necessarily require a general pattern of gluino-mediated FCNC interactions affecting both the LH and the RH sfermion sectors – the LH one being sufficient. However, given the present bounds on sparticle masses, the gluon channel turns out to lie just below the expected experimental sensibility, so our general conclusion is that the Higgs channels t→ch (especially the one for the light CP-even Higgs) have the largest potential top quark FCNC rates in the MSSM, namely of order 10−4.

Loop induced flavor changing neutral decays of the top quark in a general two Higgs doublet model

Decays of the top quark induced by flavor changing neutral currents (FCNC) are known to be extremely rare events within the Standard Model. This is so not only for the decay modes into gauge bosons, but most notably in the case of the Higgs channels, e.g., t→HSM+c, with a branching fraction of 10−13 at most. Therefore, detection of FCNC top quark decays in a future high-energy, and high-luminosity, machine like the LHC or the LC would be an indisputable signal of new physics. In this paper we show that within the simplest extension of the SM, namely the general two-Higgs-doublet model, the FCNC top quark decays into Higgs bosons, t→(h0,H0,A0)+c, can be the most favored FCNC modes — comparable or even more efficient than the gluon channel t→g+c. In both cases the optimal results are obtained for Typexa0II models. However, only the Higgs channels can have rates reaching the detectable level (10−5), with a maximum of order 10−4 which is compatible with the charged Higgs bounds from radiative B-meson decays. We compare with the previous results obtained in the Higgs sector of the MSSM.

One-loop renormalization of the electroweak parameters in N = 1 supersymmetry

Abstract We present the complete calculation of the radiative corrections to the one-loop order of the electroweak parameters in N = 1 supersymmetry. The general formulas for the resulting weak boson mass shifts are explicitly given and some special cases of possible phenomenological relevance are surveyed. The general conclusion at which we arrive is that one always ends up by finding a few hundred MeV maximal effect on the weak boson mass shifts, i.e., much smaller than the corresponding effect obtained in the standard model.

Quantum effects on \(t\rightarrow H^{+}\,b\) in the MSSM: a window to “virtual” supersymmetry?

Abstract. We analyze the one-loop effects (strong and electroweak) on the unconventional top quark decay mode n

First evidence of running cosmic vacuum: challenging the concordance model

trightarrow H^{+}, b

STRONG EFFECTS ON THE HADRONIC WIDTHS OF THE NEUTRAL HIGGS BOSONS IN THE MSSM

within the MSSM. The results are presented in the on-shell renormalization scheme with a physically well motivated definition of n

Yukawa-coupling corrections to scalar quark decays

tanbeta

Supersymmetric electroweak renormalization of the Z-width in the MSSM

. The study of this process at the quantum level is useful to unravel the potential supersymmetric nature of the charged Higgs emerging from that decay. As compared with the standard mode n

Supersymmetric QCD corrections to the charged Higgs boson decay of the top quark

trightarrow W^{+},b