20 research outputs found
Cosmological Origin for Cosmic Rays Above eV
The cosmic ray spectrum at , reported by the
Fly's Eye and the AGASA experiments, is shown to be consistent with a
cosmological distribution of sources of protons, with a power law generation
spectrum and energy production rate of
. The two
events measured above are not inconsistent with this model.
Verifying the existence of a ``black-body cutoff'', currently observed with low
significance, would require observation-years with existing
experiments, but only year with the proposed
detectors. For a cosmological source distribution, no anisotropy is expected in
the angular distribution of events with energies up to .Comment: uuencoded gz-compressed postscript file, including 2 figures; To
appear in the October 10 (1995) issue of the Ap. J. Letter
Failure of Mean Field Theory at Large N
We study strongly coupled lattice QCD with colors of staggered fermions
in 3+1 dimensions. While mean field theory describes the low temperature
behavior of this theory at large , it fails in the scaling region close to
the finite temperature second order chiral phase transition. The universal
critical region close to the phase transition belongs to the 3d XY universality
class even when becomes large. This is in contrast to Gross-Neveu models
where the critical region shrinks as (the number of flavors) increases and
mean field theory is expected to describe the phase transition exactly in the
limit of infinite . Our work demonstrates that close to second order phase
transitions infrared fluctuations can sometimes be important even when is
strictly infinite.Comment: 4 pages, 3 figure
De Sitter Cosmic Strings and Supersymmetry
We study massive spinor fields in the geometry of a straight cosmic string in
a de Sitter background. We find a hidden N=2 supersymmetry in the fermionic
solutions of the equations of motion. We connect the zero mode solutions to the
heat-kernel regularized Witten index of the supersymmetric algebra.Comment: Version similar to the one accepted by General Relativity and
Gravitatio
Onset of Delocalization in Quasi-1D Waveguides with Correlated Surface Disorder
We present first analytical results on transport properties of many-mode
waveguides with rough surfaces having long-range correlations. We show that
propagation of waves through such waveguides reveals a quite unexpected
phenomena of a complete transparency for a subset of propagating modes. These
modes do not interact with each other and effectively can be described by the
theory of 1D transport with correlated disorder. We also found that with a
proper choice of model parameters one can arrange a perfect transparency of
waveguides inside a given window of energy of incoming waves. The results may
be important in view of experimental realizations of a selective transport in
application to both waveguides and electron/optic nanodevices.Comment: RevTex, 4 pages, no figures, few references are adde
Dynamical Chiral Symmetry Breaking on a Brane in Reduced QED
Reduced gauge theories are theories in which while gauge fields propagate in
a bulk, fermion fields are localized on a brane. We study dynamical chiral
symmetry breaking on a 2-brane and a 1-brane in reduced QED_{3+1}, and on a
1-brane in reduced QED_{2+1}. Since, unlike higher dimensional gauge theories,
QED_{3+1} and QED_{2+1} are well defined, their reduced versions can serve as a
laboratory for studying dynamics in a higher dimensional brane world. The
analysis of the Schwinger-Dyson (SD) equations in these theories reveals rich
and quite nontrivial dynamics in which the conformal symmetry and its breakdown
play a crucial role. Explicit solutions of the SD equations in the
near-critical regime are obtained and the character of the corresponding phase
transition is described.Comment: PRD versio
d_{x^2-y^2}-Wave Pairing Fluctuations and Pseudo Spin Gap in Two-Dimensional Electron Systems
Pseudogap phenomena of high-T_c cuprates are examined. In terms of AFM
(antiferromagnetic) and dSC (d_{x^2-y^2}-wave superconducting) auxiliary fields
introduced to integrate out the fermions, the effective action for 2D electron
systems with AFM and dSC fluctuations is considered. By the self-consistent
renormalization (SCR), the NMR relaxation rate T_1^{-1}, the spin correlation
length \xi_\sigma and the pairing correlation length \xi_d are calculated. From
this calculation, a mechanism of the pseudogap formation emerges as the region
of dominant d-wave short-range order (SRO) over AFM-SRO. When damping for the
AFM fluctuation strongly depends on the dSC correlation length through the
formation of precursor singlets around (\pi,0) and (0,\pi) points in the
momentum space, the pseudogap appears in a region of the normal state
characterized by decreasing 1/T_1T and increasing AFM correlation length with
decrease in temperature. This reproduces a characteristic feature of the
pseudogap phenomena in many underdoped cuprates. When the damping becomes
insensitive to the dSC correlation length, the pseudogap region shrinks as in
the overdoped cuprates.Comment: 13 pages with 5 figures, submitted to J. Phys. Soc. Jpn.; figure
inclusion correcte
Lessons from : Vacuum structure, Asymptotic Series, Instantons and all that
We discuss two dimensional with fermions in the
fundamental as well as adjoint representation. We find factorial growth in the coefficients of
the large order perturbative expansion. We argue that this behavior is related
to classical solutions of the theory, instantons, thus it has nonperturbative
origin. Phenomenologically such a growth is related to highly excited states in
the spectrum. We also analyze the heavy-light quark system within
operator product expansion (which it turns out to be an asymptotic series).
Some vacuum condensates \la\bar{q}(x_{\mu}D_{\mu})^{2n}q\ra\sim (x^2)^n\cdot
n! which are responsible for this factorial growth are also discussed. We
formulate some general puzzles which are not specific for 2D physics, but are
inevitable features of any asymptotic expansion. We resolve these apparent
puzzles within and we speculate that analogous puzzles might occur in
real 4-dimensional QCD as well.Comment: latex, 26 pages. A final version to appear in Phys. Rev.
Neutrinos produced by ultrahigh-energy photons at high red shift
Some of the proposed explanations for the origin of ultrahigh-energy cosmic
rays invoke new sources of energetic photons (e.g., topological defects, relic
particles, etc.). At high red shift, when the cosmic microwave background has a
higher temperature but the radio background is low, the ultrahigh-energy
photons can generate neutrinos through pair-production of muons and pions.
Neutrinos produced at high red shift by slowly evolving sources can be
detected. Rapidly evolving sources of photons can be ruled out based on the
existing upper limit on the neutrino flux.Comment: 4 pages, revtex; to appear in Phys. Rev. Let