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A. Rossi

Publications and source records attributed to A. Rossi.

209 records · Page 12Linked to original sources
arXiv1999

A novel iterative strategy for protein design

We propose and discuss a novel strategy for protein design. The method is based on recent theoretical advancements which showed the importance to treat carefully the conformational free energy of designed sequences. In this work we show how computational cost can be kept to a minimum by encompassing negative design features, i.e. isolating a small number of structures that compete significantly with the target one for being occupied at low temperature. The method is succesfully tested on minimalist protein models and using a variety of amino acid interaction potentials.

cond-mat.stat-mech↗
arXiv1998

Effective potential for dissipative quantum systems

We consider quantum nonlinear systems with dissipation described within the Caldeira-Leggett model, i.e., by a nonlocal action in the path integral for the density matrix. Approximate classical-like formulas are derived in order to evaluate thermal averages of observables: the cases of linear and nonlinear dissipation are considered, and the framework is extended to the case of many degrees of freedom.

cond-mat.stat-mech↗
arXiv1997

Supernova Bounds on Resonant Active-Sterile Neutrino Conversions

We discuss the effects of resonant $ν_e \to ν_s$ and $\barν_e \to \barν_s$ ($ν_s$ is a sterile neutrino) conversions in the dense medium of a supernova. In particular, we assume the sterile neutrino $ν_s$ to be in the hot dark matter few eV mass range. The implications of such a scenario for the supernova shock re-heating, the detected $\barν_e$ signal from SN1987A and for the r-process nucleosynthesis hypothesis are analysed in some detail. The resulting constraints on mixing and mass difference for the $ν_e-ν_s$ system are derived. There is also an allowed region in the neutrino parameter space for which the r-process nucleosynthesis can be enhanced.

hep-ph↗
arXiv1996

The MSW conversion of solar neutrinos and random matter density perturbations

We present a generalization of the resonant neutrino conversion in matter, including a random component in the matter density profile. The study is focused on the effect of such matter perturbations upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \to ν_{μ,τ}$ as well as active-sterile $ν_e \to ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $δm^2$) than the large mixing solution. Future solar neutrino experiments, such as Borexino, could probe solar matter density noise at the few percent level.

hep-ph↗
arXiv1996

Supernova Bounds on Supersymmetric $R$-parity Violating Interactions

We re-examine resonant massless-neutrino conversions in a dense medium induced by flavour changing neutral current (FCNC) interactions. We show how the observed $\barν_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis provide constraints on supersymmetric models with $R$ parity violation, which are much more stringent than those obtained from the laboratory. We also suggest that resonant massless-neutrino conversions may play a positive role in supernova shock reheating. Finally, we examine the constraints on explicit $R$-parity-violating FCNCs in the presence of non-zero neutrino masses in the eV range, as indicated by present hot dark matter observations.

hep-ph↗
arXiv1996

The stability of the MSW solution to the solar neutrino problem with respect to random matter density perturbations

We present a generalization of the resonant neutrino conversion in matter, including a random component in the matter density profile. The study is focused on the effect of such matter perturbations upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \ra ν_{μ,τ}$ as well as active-sterile $ν_e \ra ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $δm^2$) than the large mixing solution. Future solar neutrino experiments, such as Borexino, could probe solar matter density noise at the few percent level.

hep-ph↗
arXiv1996

Resonant Conversion of Massless Neutrinos in Supernovae

It has been noted for a long time that, in some circumstances, {\sl massless} neutrinos may be {\sl mixed} in the leptonic charged current. Conventional neutrino oscillation searches in vacuum are insensitive to this mixing. We discuss the effects of resonant massless-neutrino conversions in the dense medium of a supernova. In particular, we show how the detected $\barν_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis may be used to provide very stringent constraints on the mixing of {\sl massless} neutrinos.

hep-ph↗
arXiv1996

The effect of random matter density perturbations on the MSW solution to the solar neutrino problem

We consider the implications of solar matter density random noise upon resonant neutrino conversion. The evolution equation describing MSW-like conversion is derived in the framework of the Schrödinger approach. We study quantitatively their effect upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \ra ν_{μ,τ}$ as well as active-sterile $ν_e \ra ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $Δm^2$) than the large mixing solution. The possible existence of solar matter density noise at the few percent level could be tested at future solar neutrino experiments, especially Borexino.

hep-ph↗
arXiv1994

Vacuum oscillation solution to the solar neutrino problem in standard and non-standard pictures

The neutrino long wavelength (just-so) oscillation is revisited as a solution to the solar neutrino problem. We consider just-so scenario in various cases: in the framework of the solar models with relaxed prediction of the boron neutrino flux, as well as in the presence of the non-standard weak range interactions between neutrino and matter constituents. We show that the fit of the experimental data in the just-so scenario is not very good for any reasonable value of the $^8B$ neutrino flux, but it substantially improves if the non-standard $τ$-neutrino--electron interaction is included. These new interactions could also remove the conflict of the just-so picture with the shape of the SN 1987A neutrino spectrum. Special attention is devoted to the potential of the future real-time solar neutrino detectors as are Super-Kamiokande, SNO and BOREXINO, which could provide the model independent tests for the just-so scenario. In particular, these imply specific deformation of the original solar neutrino energy spectra, and time variation of the intermediate energy monochromatic neutrino ($^7Be$ and $pep$) signals.

hep-ph↗