Experimental limit on the cosmic diffuse ultrahigh energy neutrino flux

We report results from 120 h of live time with the Goldstone lunar ultrahigh energy neutrino experiment (GLUE). The experiment searches for < or = 10 ns microwave pulses from the lunar regolith, appearing in coincidence at two large radio telescopes separated by 22 km and linked by optical fiber. Such pulses would arise from subsurface electromagnetic cascades induced by interactions of > or = 100 EeV (1 EeV = 10(18) eV neutrinos in the lunar regolith. No candidates are yet seen, and the implied limits constrain several current models for ultrahigh energy neutrino fluxes.     

Neutrino self-energy operator in plasmas at ultrahigh energies

A general expression for the neutrino self-energy operator in plasmas was obtained in the limit of ultrahigh energies. Quantitative estimations were performed for the boundaries of the region kinematically allowed for the “neutrino-spin-light” process. An analysis of the additional neutrino energy in plasmas revealed that, in the cases where neutrino spin light was kinematically allowed, the processes $\bar v_e + e^ - \to W^ -$ and $\bar v_\ell + v_\ell \to Z$ would be dominant.     

High-energy QCD asymptotic behavior of photon-photon collisions

Complex quasienergy and level width are calculated for a weakly bound atomic state in an intense circularly polarized monochromatic laser field using the method suggested by Zel’dovich for the regularization of divergent integrals with the Gamow wave function. It is demonstrated that this method converges, and the conditions for its applicability are indicated. These results are used to discuss the accuracy of the semiclassical approximation in the problems of ionization theory.     

Neutrino exchange and asymptotic behaviour of weak interaction cross sections

It is argued that total cross sections cannot increase asymptotically as a power of energy even in the presence of massless particle exchange. Elastic νν scattering is considered as an example. The properties of s- and t-channel partial waves are analysed and it is shown that the above statement is true if the amplitude is bounded by a polynomial in s for s→∞ and t>0 and if its singularity at t=0 is dominated by two-particle exchange.     

The chiral limit of quenched lattice QCD

We investigate the low mass properties of our quenched QCD data for the range of beta values: 5.70, 6.00, 6.15 and 6.30. The chiral condensate, the ground-state meson spectrum and the scaling behaviour of various quantities are examined. A criterion for assessing at what value of the quark mass finite lattice effects become intolerable is suggested.     

Two-photon detachment cross-section of atoms in the extended asymptotic model

Summary A previously proposed one-electron model for photoionization, referred to as extended asymptotic model [J. Mol. Struct. (Teochem) 166, 369 (1988)], is further developed to cope with two-photon ionization processes. A simple application of the approach to the case of the negative ion H⁻ is investigated and discussed. The authors of this paper have agreed to not receive the proofs for correction.     

Upper limit on the diffuse flux of ultrahigh energy tau neutrinos from the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E(nu)(-2) differential energy spectrum the limit set at 90% C.L. is E(nu)(2)dN(nu)(tau)/dE(nu)<1.3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E(nu)< 2 x 10(19) eV.     

Nonanalyticity in scale in the planar limit of QCD

Using methods of numerical lattice gauge theory we show that, in the limit of a large number of colors, properly regularized Wilson loops have an eigenvalue distribution which changes nonanalytically as the overall size of the loop is increased. This establishes a large-N phase transition in continuum planar gauge theory, a fact whose precise implications remain to be worked out.     

An infrared renormalization group limit cycle in QCD

We use effective field theories to show that small increases in the up and down quark masses would move QCD very close to the critical renormalization group trajectory for an infrared limit cycle in the three-nucleon system. We conjecture that QCD can be tuned to the critical trajectory by adjusting the quark masses independently. At the critical values of the quark masses, the binding energies of the deuteron and its spin-singlet partner would be tuned to zero and the triton would have infinitely many excited states with an accumulation point at the 3-nucleon threshold. The ratio of the binding energies of successive states would approach a universal constant that is close to 515.     

Cosmic rays of ultrahigh energy

A new phenomenon—giant air showers of energy above 10²⁰ eV,which lie beyond the Greisen-Zatsepin-Kuzmin cutoff—was discovered by various detection methods. The mechanism of particle acceleration to such high energies is still a puzzle. The arrival directions of giant showers do not contradict the hypothesis of their isotropic distribution. There are indications of their correlations with distant objects. It is obvious that only observations at new arrays can clarify the problem. The observed events must be reanalyzed within a more elaborate scheme. Verification of slight deviations from Lorentz invariance is possible.     

The electromagnetic mass difference of pions from asymptotic QCD

We investigate the Dirac-Kähler operator on a triangular lattice in two dimensions and show that the number of degrees of freedom which survive in the continuum limit is the same as in the case of a square lattice.     

Neutrino—nucleon cross-section at ultra-high energies in models with large extra dimensions

We examine whether the models with large extra dimensions can provide an explanation for the GZK violating ultra-high energy cosmic rays (UHECR). In these models the neutrino—nucleon cross-section rises rapidly with energy and hence cosmic rays might be identified with neutrinos. We calculate the neutrino-nucleon cross-section at ultra high energies by assuming that it is dominated by the production ofp-branes. We perform the calculation in a generalized Randall-Sundrum model and Lykken-Randall model and find cross-sections of the order of 100 mb at neutrino energies of 10²⁰ eV, which is required for explaining UHECR events.     

Neutrino condensate as origin of dark energy

We propose a new solution to the origin of dark energy. We suggest that it was created dynamically from the condensate of a singlet neutrino at a late epoch of the early Universe through its effective self-interaction. This singlet neutrino is also the Dirac partner of one of the three observed neutrinos, hence dark energy is related to neutrino mass. The onset of this condensate formation in the early Universe is also related to matter density and offers an explanation of the coincidence problem of why dark energy (70%) and total matter (30%) are comparable at the present time. We demonstrate this idea in a model of neutrino mass with (right-handed) singlet neutrinos and a singlet scalar.