Modern Physics Letters A

The problem of the damping of the Giant Dipole Resonance (GDR) at finite temperature at T>2 MeV is discussed here. The experimental results are based on fusion evaporation reactions. The most recent results on the mass region A = 132 (Ce isotopes) obtained in exclusive measurements are compared with the existing results on the A = 110–120 region (Sn isotopes). The comparison with the theoretical predictions based on thermal shape fluctuations is also discussed. The GDR width is found to increase also in the region T>2 MeV and this is accounted by the combined effect of the increase of the compound nucleus width (smaller lifetime) and to the increase of the average deformation of the nucleus.

Approximative analytic solutions of the Dirac equation in the geometry of Schwarzschild black holes are derived obtaining information about the discrete energy levels and the asymptotic behavior of the energy eigenspinors.

We suggest the possibility that the anomalies observed in the LSND experiment and the Gallium radioactive source experiments may be due to neutrino oscillations generated by a large squared-mass difference of about 20–30 eV². We consider the simplest 3+1 four-neutrino scheme that can accommodate also the observed solar and atmospheric neutrino oscillations. We show that, in this framework, the disappearance of and in short-baseline neutrino oscillation experiments is mainly due to active-sterile transitions. The implications of the first MiniBooNE results, appeared after the completion of this paper, are discussed in an addendum.

We accurately derive the fermion resonance propagator by means of Dyson summation of the self-energy contribution. It turns out that the relativistic fermion resonance differs essentially from its boson analog.

We comment on the changes in the constrained model studied earlier when constituent massless vector fields are introduced. The new model acts like a gauge-Higgs–Yukawa system, although its origin is different.

Inspired by a new class of walking technicolor models recently proposed using higher-dimensional technifermions, we consider the oblique corrections from heavy nondegenerate fermions with two classes of higher-dimensional representations of the electroweak gauge group itself. One is chiral SM-like, and the other is vector-like. In both cases, we obtain explicit expressions for S, T, U in terms of the fermion masses. We find that to keep the T parameter ultraviolet-finite, there must be a stringent constraint on the mass nondegeneracy of a heavy fermion multiplet.

If N = 2 supersymmetry breaks to N = 1 supersymmetry at an intermediate scale m₂ and then, later on, N = 1 supersymmetry breaks and produces standard model at a scale m_susy such that m₂>m_susy, renormalization group evolution of three gauge couplings are altered above the scale m₂, changing the unification scale and the unified coupling. We show that when we enforce this general condition m₂>m_susy on the solutions of the renormalization group equations, the condition is translated into an upper bound on the scale m_susy. Using presently favored values of α₁(m_z), α₂(m_z), α₃(m_z), we get m_susy < 4.5 ×10⁹ GeV for the central value of α₃(m_Z). When low energy threshold effect is present, this bound gets smeared yet remains generally stable in the 10⁹–10¹⁰ GeV range. We also show that if we demand string unification instead of having a unified gauge theory, this constraint can be changed by exotic hypercharge normalizations.