arXiv subjects

S. Lola

Publications and source records attributed to S. Lola.

60 records · Page 4Linked to original sources

arXiv1995

Textures for Neutrino Mass Matrices

We give a classification of heavy Majorana neutrino mass matrices with up to three texture zeroes, assuming the Dirac masses of the neutrinos to be of the same form as the ones of the up-quarks in the five texture zero solutions for the quark matrices. This is the case for many unified and partially unified models. We find that it is possible to have solutions which account for the solar and atmospheric neutrino problems as well as the COBE observations simultaneously, and we motivate the existence of such solutions from symmetries.

hep-ph↗

arXiv1995

Heavy neutrino threshold effects in low energy phenomenology

Right handed neutrinos with mass of ${\cal O} \; (10^{12}-10^{13})$ GeV are required to implement the see-saw mechanism and generate neutrino masses capable of playing a role in structure formation. Moreover models of fermion masses often relate the Yukawa couplings involving these neutrinos to the up-quark Yukawa couplings. Here we study the effects of such couplings on the radiative corrections to quark masses. We find that $b-τ$ equality at $M_{GUT}$ may still give the correct $m_b/m_τ$-- ratio at low energies, but only if there is large $μ-τ$ mixing in the charged leptonic sector. We propose specific mass matrix ``textures'' dictated by a $U(1)$ family symmetry whose structure preserves $m_b=m_τ$ at $M_{GUT}$. In these schemes, due to the large $ν_μ - ν_τ$ mixing, it is possible to give a simultaneous solution to the solar neutrino deficit and the atmospheric neutrino problem.

hep-ph↗

arXiv1995

Inflation from superstrings

We investigate the possibility of obtaining inflationary solutions of the slow roll type from a low energy Lagrangian coming from superstrings. The advantage of such an approach is that in these theories the scalar potential has only one free parameter (the Planck scale) and therefore no unnatural fine tuning may be accommodated. We find that in any viable scheme the dilaton and the moduli fields have to be stabilized and that before this happens, no other field may be used as the inflaton. Then inflation may occur due to chiral matter fields. Demanding that the potential terms associated with the chiral fields do not spoil the dilaton and moduli minimization leads to severe constraints on the magnitude of the density fluctuations.

hep-ph↗

arXiv1995

PHASE TRANSITION OF N-COMPONENT SUPERCONDUCTORS

We investigate the phase transition in the three-dimensional abelian Higgs model for N complex scalar fields, using the gauge-invariant average action Γ_{k}. The dependence of Γ_{k} on the effective infra-red cut-off k is described by a non-perturbative flow equation. The transition turns out to be first- or second-order, depending on the ratio between scalar and gauge coupling. We look at the fixed points of the theory for various N and compute the critical exponents of the model. Comparison with results from the ε-expansion shows a rather poor convergence for ε=1 even for large N. This is in contrast to the surprisingly good results of the ε-expansion for pure scalar theories. Our results suggest the existence of a parameter range with a second-order transition for all N, including the case of the superconductor phase transition for N=1.

cond-mat↗

arXiv1994

Neutrino Masses from Gauge Symmetries

A very simple extension of the standard model to include an Abelian family symmetry is able to describe the hierarchy of quark and lepton masses and their mixing angles together with the unification of gauge couplings. We consider the implications of this model for neutrino masses and mixing angles and show that they are determined up to a discrete ambiguity corresponding to the representation content of the Higgs sector responsible for the Majorana mass matrix.

hep-ph↗

arXiv1994

Large scale structure from biased non-equilibrium phase transitions - percolation theory picture

We give an analytical description of the spatial distribution of domain walls produced during a biased nonequilibrium phase transition in the vacuum state of a light scalar field. We discuss in detail the spectrum of the associated cosmological energy density perturbations. It is shown that the contribution coming from domain walls can enhance the standard cold dark matter spectrum in such a way as to account for the whole range of IRAS data and for the COBE measurement of the microwave background anisotropy. We also demonstrate that in case of a biased phase transition which allows a percolative description, the number of large size domain walls is strongly suppressed. This offers a way of avoiding excessive microwave background distorsions due to the gravitational field of domain walls present after decoupling.

hep-ph↗