Background thermal depolarization of electrons in storage rings

We discuss the influence of the background thermal bath on the depolarization of electrons in high-energy storage rings, and on the photon emission associated with the spin flip. We focus, in particular, on electrons at CERN LEP. We show that in a certain interval of solid angles the photon emission is enhanced several orders of magnitude because of the presence of the thermal bath. Notwithstanding, the overall depolarization induced by the background thermal bath at LEP conditions is much smaller than the one induced by plain acceleration at zero temperature and can be neglected in practical situations. Eventually we discuss under what conditions the background thermal bath can enhance the overall depolarization by several orders of magnitude.

Note on the point-splitting procedure to evaluate vacuum fluctuation in certain cylindrically symmetric backgrounds

We reexamine the two-point function approaches used to study vacuum fluctuation in wedge-shaped regions and conical backgrounds. The appearance of divergent integrals is discussed and circumvented. The issue is considered in the context of a massless scalar field in cosmic string spacetime.

Update on atmospheric neutrinos

We discuss the impact of recent experimental results on the determination of atmospheric neutrino oscillation parameters. We use all published results on atmospheric neutrinos, including the preliminary large statistics data of Super-Kamiokande. We reanalyze the data in terms of both vμ → vτ and vμ → ve channels using new improved calculations of the atmospheric neutrino flux. We compare the sensitivity attained in atmospheric neutrino experiments with those of accelerator and reactor neutrino oscillation searches, including the recent CHOOZ experiment. We briefly comment on the implications of atmospheric neutrino data in relation to future searches for neutrino oscillations with long baselines, such as the K2K, MINOS, ICARUS, and NOE experiments.

Tests of anomalous quartic couplings at the Next Linear Collider

We analyze the potential of the Next Linear e+e- Collider to study anomalous quartic vector-boson interactions through the processes e+e-→W+W-Z and ZZZ. In the framework of SU(2)L⊗U(1)Y chiral Lagrangians, we examine all effective operators of order p4 that lead to four-gauge-boson interactions but do not induce anomalous trilinear vertices. In our analysis, we take into account the decay of the vector bosons to fermions and evaluate the efficiency in their reconstruction. We obtain the bounds that can be placed on the anomalous quartic interactions and we study the strategies to distinguish the possible couplings.

Electric charge quantization in a chiral bilepton gauge model

In the context of the standard model the quantization of the electric charge occurs only family by family. When we consider the three families together with massless neutrinos the electric charge is not quantized any more. Here we show that a chiral bilepton gauge model based on the gauge group SU(3)C ⊗ SU(3)L ⊗ U(1)N explains the quantization of the electric charge when we take into account the three families of fermions. This result does not depend on the neutrino masses. Charge quantization occurs whether the neutrinos are massless or Dirac or Majorana massive fields.

Constraints on free parameters of the simplest bilepton gauge model from the neutral kaon system mass difference

We consider the contributions of the exotic quarks and gauge bosons to the mass difference between the short- and the long-lived neutral kaon states in the SU(3)C×SU(3)L×U(1)N model. The lower bound MZ′∼14 TeV is obtained for the extra neutral gauge boson Z′0. Ranges for values of one of the exotic quark masses and quark mixing parameters are also presented.

Interaction of Hawking radiation and a static electric charge

We investigate whether the equality found for the response of static scalar sources interacting (i) with Hawking radiation in Schwarzschild spacetime and (ii) with the Fulling-Davies-Unruh thermal bath in the Rindler wedge is maintained in the case of electric charges. We find a finite result in the Schwarzschild case, which is computed exactly, in contrast with the divergent result associated with the infrared catastrophe in the Rindler case, i.e., in the case of uniformly accelerated charges in Minkowski spacetime. Thus the equality found for scalar sources does not hold for electric charges.

Interaction of Hawking radiation with static sources outside a Schwarzschild black hole

We show that the response rate of (i) a static source interacting with Hawking radiation of a massless scalar field in Schwarzschild spacetime (with the Unruh vacuum) and that of (ii) a uniformly accelerated source with the same proper acceleration in Minkowski spacetime (with the Minkowski vacuum) are equal. We show that this equality will not hold if the Unruh vacuum is replaced by the Hartle-Hawking vacuum. It is verified that the source responds to the Hawking radiation near the horizon as if it were at rest in a thermal bath in Minkowski spacetime with the same temperature. It is also verified that the response rate in the Hartle-Hawking vacuum approaches that in Minkowski spacetime with the same temperature far away from the black hole. Finally, we compare our results with others in the literature.

Left-right asymmetries in polarized lepton-lepton scattering

Several parity-violating left-right asymmetries in Miller electron-electron and muon-muon scattering are considered in the context of the electroweak standard model at the tree level in fixed target and collider experiments. We show that in colliders the asymmetry with only one of the beams polarized is large enough to compensate the smaller cross section at high energies. We also show that these asymmetries are very sensitive to a doubly charged vector bilepton resonance but they are insensitive to scalar ones.

Signal and backgrounds for the single production of scalar and vector leptoquarks at the CERN LHC

We perform a detailed analysis of the potentiality of the CERN Large Hadron Collider to study the single production of leptoquarks via pp→e±q→ leptoquark →e± q, with e± generated by the splitting of photons radiated by the protons. Working with the most general SU(2)L⊗U( 1 )Y invariant effective Lagrangian for scalar and vector leptoquarks, we analyze in detail the leptoquark signals and backgrounds that lead to a final state containing an e± and a hard jet with approximately balanced transverse momenta. Our results indicate that the LHC will be able to discover leptoquarks with masses up to 2-3 TeV, depending on their type, for Yukawa couplings of the order of the electromagnetic one.

Are two gluons the QCD Pomeron?

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Gerasimov-Drell-Hearn sum rule and the single-pion photoproduction multipole E0+ close to threshold

The long-standing discrepancy between the Gerasimov-Drell-Hearn sum rule and the analysis of pion photoproduction multipoles is greatly diminished by use of s-wave multipoles that are in accord with the predictions of chiral perturbation theory and describe the experimental data in the threshold region. The remaining difference may be due to contributions of channels with more pions and/or heavier mesons whose contributions to the sum rule remain to be investigated by a direct measurement of the photoabsorption cross sections.

Model for stars of interacting bosons and fermions

In this paper we introduce a current-current type interaction term in the Lagrangian density of gravity coupled to complex scalar fields, in the presence of a degenerated Fermi gas. For low transferred momenta, such a term, which might account for the interaction among boson and fermion constituents of compact stellar objects, is subsequently reduced to a quadratic one in the scalar sector. This procedure enforces the use of a complex radial field counterpart in the equations of motion. The real and the imaginary components of the scalar field exhibit different behavior as the interaction increases. The results also suggest that the Bose-Fermi system undergoes a phase transition for a suitable choice of the coupling constant.

Relations between two-dimensional models from dimensional reduction

In this work we explore the consequences of dimensional reduction of the 3D Maxwell-Chern-Simons and some related models. A connection between topological mass generation in 3D and mass generation according to the Schwinger mechanism in 2D is obtained. In addition, a series of relationships is established by resorting to dimensional reduction and duality interpolating transformations. Non-Abelian generalizations are also pointed out.

Strongly interacting vector bosons at the CERN LHC: Quartic anomalous couplings

We analyze the potential of the CERN Large Hadron Collider to study anomalous quartic vector-boson interactions through the production of vector-boson pairs accompanied by jets. In the framework of SU(2) L⊗U(1) Y chiral Lagrangians, we examine all effective operators of order p 4 that lead to new four-gauge-boson interactions but do not alter trilinear vertices. In our analyses, we perform the full tree-level calculation of the processes leading to two jets plus vector-boson pairs, W +W -,W ±W ±,W ±Z, or ZZ, taking properly into account the interference between the standard model and the anomalous contributions. We obtain the bounds that can be placed on the anomalous quartic interactions and we study the strategies to distinguish the possible new couplings. ©1998 The American Physical Society.