535 research outputs found
Monte Carlo simulation for jet fragmentation in SUSY-QCD
We present results from a new Monte Carlo simulation for jet fragmentation in
QCD and SUSY QCD for large primary energies up to GeV. In
the case of SUSY QCD the simulation takes into account not only gluons and
quarks as cascading particles, but also their supersymmetric partners. A new
model-independent hadronization scheme is developed, in which the hadronization
functions are found from LEP data. An interesting feature of SUSY QCD is the
prediction of a sizeable flux of the lightest supersymmetric particles (LSPs),
if R-parity is conserved. About 10% of the jet energy is transferred to LSPs
which, owing to their harder spectra, constitute an important part of the
spectra for large . Spectra of protons and of secondary particles,
photons and neutrinos, are also calculated. These results have implications for
the decay of superheavy particles with masses up to the GUT scale, which have
been suggested as a source of ultrahigh energy cosmic rays.Comment: latex, 25 pages with 17 eps figure
Distribution of local density of states in disordered metallic samples: logarithmically normal asymptotics
Asymptotical behavior of the distribution function of local density of states
(LDOS) in disordered metallic samples is studied with making use of the
supersymmetric --model approach, in combination with the saddle--point
method. The LDOS distribution is found to have the logarithmically normal
asymptotics for quasi--1D and 2D sample geometry. In the case of a quasi--1D
sample, the result is confirmed by the exact solution. In 2D case a perfect
agreement with an earlier renormalization group calculation is found. In 3D the
found asymptotics is of somewhat different type: P(\rho)\sim
\exp(-\mbox{const}\,|\ln^3\rho|).Comment: REVTEX, 14 pages, no figure
Bethe-Sommerfeld conjecture for periodic operators with strong perturbations
We consider a periodic self-adjoint pseudo-differential operator
, , in which satisfies the following conditions:
(i) the symbol of is smooth in \bx, and (ii) the perturbation has
order less than . Under these assumptions, we prove that the spectrum of
contains a half-line. This, in particular implies the Bethe-Sommerfeld
Conjecture for the Schr\"odinger operator with a periodic magnetic potential in
all dimensions.Comment: 61 page
Mass Suppression in Octet Baryon Production
There is a striking suppression of the cross section for production of octet
baryons in annihilation, as the mass of the produced hadron
increases. We present a simple parametrization for the fragmentation functions
into octet baryons guided by two input models: the SU(3) flavor symmetry part
is given by a quark-diquark model, and the baryon mass suppression part is
inspired by the string model. We need only eight free parameters to describe
the fragmentation functions for all octet baryons. These free parameters are
determined by a fit to the experimental data of octet baryon production in annihilation. Then we apply the obtained fragmentation functions to
predict the cross section of the octet baryon production in charged lepton DIS
and find consistency with the available experimental data. Furthermore, baryon
production in collisions is suggested to be an ideal domain to check the
predicted mass suppression.Comment: 20 pages, 5 figure
A glassy contribution to the heat capacity of hcp He solids
We model the low-temperature specific heat of solid He in the hexagonal
closed packed structure by invoking two-level tunneling states in addition to
the usual phonon contribution of a Debye crystal for temperatures far below the
Debye temperature, . By introducing a cutoff energy in the
two-level tunneling density of states, we can describe the excess specific heat
observed in solid hcp He, as well as the low-temperature linear term in the
specific heat. Agreement is found with recent measurements of the temperature
behavior of both specific heat and pressure. These results suggest the presence
of a very small fraction, at the parts-per-million (ppm) level, of two-level
tunneling systems in solid He, irrespective of the existence of
supersolidity.Comment: 11 pages, 4 figure
Nonperturbative Effects in Gluon Radiation and Photoproduction of Quark Pairs
We introduce a nonperturbative interaction for light-cone fluctuations
containing quarks and gluons. The interaction squeezes the transverse
size of these fluctuations in the photon and one does not need to simulate this
effect via effective quark masses. The strength of this interaction is fixed by
data. Data on diffractive dissociation of hadrons and photons show that the
nonperturbative interaction of gluons is much stronger. We fix the parameters
for the nonperturbative quark-gluon interaction by data for diffractive
dissociation to large masses (triple-Pomeron regime). This allows us to predict
nuclear shadowing for gluons which turns out to be not as strong as
perturbative QCD predicts. We expect a delayed onset of gluon shadowing at shadowing of quarks. Gluon shadowing turns out to be nearly scale
invariant up to virtualities due to presence of a semihard
scale characterizing the strong nonperturbative interaction of gluons. We use
the same concept to improve our description of gluon bremsstrahlung which is
related to the distribution function for a quark-gluon fluctuation and the
interaction cross section of a fluctuation with a nucleon. We expect
the nonperturbative interaction to suppress dramatically the gluon radiation at
small transverse momenta compared to perturbative calculations.Comment: 58 pages of Latex including 11 figures. Shadowing for soft gluons and
Fig. 6 are added as well as a few reference
Gauge Orbit Types for Theories with Classical Compact Gauge Group
We determine the orbit types of the action of the group of local gauge
transformations on the space of connections in a principal bundle with
structure group O(n), SO(n) or over a closed, simply connected manifold
of dimension 4. Complemented with earlier results on U(n) and SU(n) this
completes the classification of the orbit types for all classical compact gauge
groups over such space-time manifolds. On the way we derive the classification
of principal bundles with structure group SO(n) over these manifolds and the
Howe subgroups of SO(n).Comment: 57 page
Hubble flows and gravitational potentials in observable Universe
In this paper, we consider the Universe deep inside of the cell of
uniformity. At these scales, the Universe is filled with inhomogeneously
distributed discrete structures (galaxies, groups and clusters of galaxies),
which disturb the background Friedmann model. We propose mathematical models
with conformally flat, hyperbolic and spherical spaces. For these models, we
obtain the gravitational potential for an arbitrary number of randomly
distributed inhomogeneities. In the cases of flat and hyperbolic spaces, the
potential is finite at any point, including spatial infinity, and valid for an
arbitrary number of gravitating sources. For both of these models, we
investigate the motion of test masses (e.g., dwarf galaxies) in the vicinity of
one of the inhomogeneities. We show that there is a distance from the
inhomogeneity, at which the cosmological expansion prevails over the
gravitational attraction and where test masses form the Hubble flow. For our
group of galaxies, it happens at a few Mpc and the radius of the
zero-acceleration sphere is of the order of 1 Mpc, which is very close to
observations. Outside of this sphere, the dragging effect of the gravitational
attraction goes very fast to zero.Comment: 21 pages, 5 figure
A Two-dimensional Superconductor in a Tilted Magnetic Field - new states with finite Cooper-pair momentum
Varying the angle Theta between applied field and the conducting planes of a
layered superconductor in a small interval close to the plane-parallel field
direction, a large number of superconducting states with unusual properties may
be produced. For these states, the pair breaking effect of the magnetic field
affects both the orbital and the spin degree of freedom. This leads to pair
wave functions with finite momentum, which are labeled by Landau quantum
numbers 0<n<\infty. The stable order parameter structure and magnetic field
distribution for these states is found by minimizing the quasiclassical free
energy near H_{c2} including nonlinear terms. One finds states with coexisting
line-like and point-like order parameter zeros and states with coexisting
vortices and antivortices. The magnetic response may be diamagnetic or
paramagnetic depending on the position within the unit cell. The structure of
the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states at Theta=0 is reconsidered.
The transition n->\infty of the paramagnetic vortex states to the FFLO-limit is
analyzed and the physical reason for the occupation of higher Landau levels is
pointed out.Comment: 24 pages, 11 figure
Transverse momentum resummation for Higgs boson produced via bb-bar fusion at hadron colliders
We study the impact of initial-state multiple parton radiation on transverse
momentum distribution of Higgs boson produced via bottom quark fusion
at hadron colliders. The shape of the resulting distribution is affected
by the bottom-quark mass corrections and by the strong kinematical behavior of
the bottom-quark parton density. We account for both features in the full range
of . To do this, we formulate the resummation calculation in a
general-mass factorization (S-ACOT) scheme and introduce a correction in the
resummed-term to account for the effect from large- kinematics of Higgs
boson. The results of this resummation are compared to fixed-order and PYTHIA
predictions.Comment: LaTex, 20 pages, 7 figure
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