arXiv subjects
Publications and source records attributed to G. Mangano.
A new accurate evaluation of primordial light nuclei abundances is presented. The proton to neutron conversion rates have been corrected to take into account radiative effects, finite nucleon mass, thermal and plasma corrections. The theoretical uncertainty on 4He is so reduced to the order of 0.1%.
We report the results of a new accurate evaluation of light nuclei yields in primordial nucleosynthesis. All radiative effects, finite nucleon mass, thermal and plasma corrections are included in the proton to neutron conversion rates. The relic densities of He4, D and Li7 have been numerically obtained via a new updated version of the standard BBN code. In particular the theoretical uncertainty on He4 is reduced to the order of 0.1%.
We report the results of a detailed calculation of nucleon weak interactions relevant for the neutron to proton density ratio at the onset of primordial nucleosynthesis. Radiative electromagnetic corrections, finite nucleon mass terms, thermal radiative effects on weak processes and on neutrino temperature are taken into account to reduce the theoretical uncertainty on $n \leftrightarrow p $ rates to 1%. This translates into a sensitivity in $^4 He$ mass fraction $Y_p$ prediction up to $10^{-4}$. We find a positive total correction to the Born prediction $δY_p \simeq 0.004$.
We present a derivation of the medium dependent wave function renormalization for a spinor field in presence of a thermal bath. We show that, as already pointed out in literature, projector operators are not multiplicatively renormalized and the effect involves a non trivial spinor dependence, which disappears in the zero temperature covariant limit. The results, which differ from what already found in literature, are then applied to the decay of a massive scalar boson into two fermions and to the $β$--decay and crossed related processes relevant for primordial nucleosynthesis.
A scheme of hybrid inflation is considered in the framework of the minimal supersymmetric SU(5) model with an extra singlet. The relevant role of the cubic term in the adjoint representation in the renormalizable superpotential is pointed out in order to have a quite wide region of initial conditions compatible with inflation efficiency, monopole density and perturbations constraint.
We review the status of a class of gauge unified models based on SO(10) group. After a pedagogical introduction to SO(10) gauge theories, we discuss the main phenomenological implications of these models. The upper limit on proton lifetime are obtained and the prediction for neutrino masses are compared with the astrophysical and cosmological constraints coming from solar neutrino data and dark matter problem. Possible scenarios for the production of the baryon asymmetry of the universe required by primordial nucleosynthesis are also discussed.
We report on some phenomenological implications of a class of unified models based on SO(10) gauge group, with intermediate symmetry group containing SU(2)_R. Interesting predictions for neutrino masses are discussed, which are relevant both for solar neutrino and dark matter problems, as well as a model for the formation of the baryon asymmetry of the universe required by primordial nucleosynthesis.
The cosmological implications of a class of SO(10) models are discussed. In particular we show how a good prediction for neutrino masses is obtained in order to fit with the MSW mechanism to explain the solar neutrino flux deficit and with the predicted amount of the dark matter hot component. A possible scenario for baryogenesis is also considered.
In a recent paper we pointed out the presence of extra fermionic degrees of freedom in a chiral gauge theory based on Connes Noncommutative Geometry. Here we propose a mechanism which provides a high mass to these mirror states, so that they decouple from low energy physics.
The resonant transition effects MSW and NSFP for three flavour Majorana neutrinos in a supernova are considered, where the transition magnetic moments are likely to play a relevant role in neutrino physics. In this scenario, the deformed thermal neutrino distributions are obtained for different choices of the electron-tau mixing angle. Detailed predictions for the future large neutrino detectors are also given in terms of the ratio between the spectra of recoil electrons for deformed and undeformed spectra.
The existence of a minimal observable length has long been suggested, in quantum gravity, as well as in string theory. In this context a generalized uncertainty relation has been derived which quantum theoretically describes the minimal length as a minimal uncertainty in position measurements. Here we study in full detail the quantum mechanical structure which underlies this uncertainty relation.
Studies in string theory and quantum gravity suggest the existence of a finite lower limit $Δx_0$ to the possible resolution of distances, at the latest on the scale of the Planck length of $10^{-35}m$. Within the framework of the euclidean path integral we explicitly show ultraviolet regularisation in field theory through this short distance structure. Both rotation and translation invariance can be preserved. An example geometry is studied in detail.
In this paper we study the structure of the Hilbert space for the recent noncommutative geometry models of gauge theories. We point out the presence of unphysical degrees of freedom similar to the ones appearing in lattice gauge theories (fermion doubling). We investigate the possibility of projecting out these states at the various levels in the construction, but we find that the results of these attempts are either physically unacceptable or geometrically unappealing.
The Connes and Lott reformulation of the strong and electroweak model represents a promising application of noncommutative geometry. In this scheme the Higgs field naturally appears in the theory as a particular `gauge boson', connected to the discrete internal space, and its quartic potential, fixed by the model, is not vanishing only when more than one fermion generation is present. Moreover, the exact hypercharge assignments and relations among the masses of particles have been obtained. This paper analyzes the possibility of extensions of this model to larger unified gauge groups. Noncommutative geometry imposes very stringent constraints on the possible theories, and remarkably, the analysis seems to suggest that no larger gauge groups are compatible with the noncommutative structure, unless one enlarges the fermionic degrees of freedom, namely the number of particles.
In the framework of the Connes-Lott model based on noncommutative geometry, the basic features of a gauge theory in the presence of gravity are reviewed, in order to show the possible physical relevance of this scheme for inflationary cosmology. These models naturally contain at least two scalar fields, interacting with each other whenever more than one fermion generation is assumed. In this paper we propose to investigate the behaviour of these two fields (one of which represents the distance between the copies of a two-sheeted space-time) in the early stages of the universe evolution. In particular the simplest abelian model, which preserves the main characteristics of more complicate gauge theories, is considered and the corresponding inflationary dynamics is studied. We find that a chaotic inflation is naturally favoured, leading to a field configuration in which no symmetry breaking occurs and the final distance between the two sheets of space-time is smaller the greater the number of $e$-fold in each sheet.
The phenomenological evidence of quantum statistical effects in parton physics is here briefly summarized, and the recent good results obtained by parameterizing the parton distributions in terms of Fermi-Dirac and Bose-Einstein statistical functions are discussed. In this framework we study the modification of the scaling behaviour of parton distributions due to quantum statistical effects. In particular, by following a well-known formal analogy which holds between the Altarelli-Parisi evolution equations, at leading-log approximation, and a set of Boltzmann equations, we suggest a generalization of evolution equations to take into account Pauli exclusion principle and gluon induced emission.
We extend a previous analysis concerning cosmological fluids with generalized equations of state in order to study inflationary scenarios. In the framework of the slow-roll approximation we find the expressions for the perturbation parameters $ε$, $η$ and the density perturbation spectra in terms of the adiabatic index $\ga$ as a function of the universe scale factor. This connection allows to find straightforwardly $\ga$ corresponding, for example, to the simplest {\it chaotic} model and to the Harrison-Zeldovich potential and shows its capability to be applied to more complicate situations. Finally, we use this description to develop a new approach to the early universe dynamics, based on a $1/N$ expansion, where $N$ is the e-fold number. To this aim, we introduce a set of suitable dimensionless variables and show that at the zero-th order in $1/N$, an improved slow-roll approximation is obtained.
Starting from the old idea that Fermi statistics for quarks play a fundamental role to explain some features of hadron structure, we study the modification of the scaling behaviour of parton distributions due to quantum statistical effects. In particular, by following an interesting formal analogy which holds between the Altarelli-Parisi evolution equations, in leading-log approximation, and a set of Boltzmann equations, we generalize the evolution equations to take into account Pauli exclusion principle and gluon induced emission.