Isosinglet neutral heavy lepton production in high energy e-γ collisions

We evaluate the potential for searching for isosinglet neutral heavy leptons (N), such as right-handed neutrinos, in the next generation of e+e- linear colliders, paying special attention to contributions from the reaction γe→WN initiated by photons from beamstrahlung and laser back-scattering. We find that these mechanisms are both competitive and complementary to the standard e+e-→vN annihilation process for producing neutral heavy leptons in these machines and greatly extends the search range over HERA and LEP200.

Searching for an invisibly decaying Higgs boson in e+e-, eγ, and γγ collisions

Higgs bosons can have a substantial invisible branching ratio in many extensions of the Standard Model, such as models where the Higgs bosons decay predominantly into light or massless weakly interacting Goldstone bosons. In this work, we examine the production mechanisms and backgrounds for invisibly decaying Higgs bosons at the Next Linear e+e- Collider operating in the modes e+e-, eγ, and γγ. We demonstrate that such machine is much more efficient to survey for invisibly decaying Higgs bosons than the Large Hadron Collider at CERN.

Soft color enhancement of the production of J/psi's by neutrinos

We calculate the production of J/ψ mesons by neutrino-nucleon collisions in fixed target experiments. Soft color, often referred to as color evaporation effects, enhances production cross sections due to the contribution of color octet states. Though still small, J/ψ production may be observable in present and future experiments such as NuTeV and μ colliders. ©2001 The American Physical Society.

Medium effects in the pion-pole mechanism [gamma gamma ->pi(0)->nu(R)(nu)over-bar(L)(nu(L)(nu)over-bar(R))] of neutron star cooling

Nuclear medium effects in the neutrino cooling of neutron stars through the reaction channel γγ→π0 →ν Rν̄L(νLν̄R) are incorporated. Throughout the paper we discuss different possibilities of right-handed neutrinos, massive left-handed neutrinos, and standard massless left-handed neutrinos (reaction is then allowed only with medium modified vertices). It is demonstrated that multiparticle effects suppress the rate of this reaction channel in the dense hadron matter by 6-7 orders of magnitude that does not allow to decrease existing experimental upper limit on the corresponding π0νν̄ coupling. Other possibilities of the manifestation of the given reaction channel in different physical situations, e.g., in the quark color superconducting cores of the most massive neutron stars, are also discussed. We demonstrate that in the color-flavor-locked superconducting phase for temperatures T≲ 0.1-10 MeV (depending on the effective pion mass and the decay width) the process is feasibly the most efficient neutrino cooling process, although the absolute value of the reaction rate is rather small.