663 research outputs found
Glauber - Gribov approach for DIS on nuclei in N=4 SYM
In this paper the Glauber-Gribov approach for deep-inelastic scattering (DIS)
with nuclei is developed in N=4 SYM. It is shown that the amplitude displays
the same general properties, such as geometrical scaling, as is the case in the
high density QCD approach. We found that the quantum effects leading to the
graviton reggeization, give rise to an imaginary part of the nucleon amplitude,
which makes the DIS in N=4 SYM almost identical to the one expected in high
density QCD. We concluded that the impact parameter dependence of the nucleon
amplitude is very essential for N=4 SYM, and the entire kinematic region can be
divided into three regions which are discussed in the paper. We revisited the
dipole description for DIS and proposed a new renormalized Lagrangian for the
shock wave formalism which reproduces the Glauber-Gribov approach in a certain
kinematic region. However the saturation momentum turns out to be independent
of energy, as it has been discussed by Albacete, Kovchegov and Taliotis. We
discuss the physical meaning of such a saturation momentum and argue
that one can consider only within the shock wave approximation.Comment: 40pp.,9 figures in eps file
Survival probability of large rapidity gaps in QCD and N=4 SYM motivated model
In this paper we present a self consistent theoretical approach for the
calculation of the Survival Probability for central dijet production . These
calculations are performed in a model of high energy soft interactions based on
two ingredients:(i) the results of N=4 SYM, which at the moment is the only
theory that is able to deal with a large coupling constant; and (ii) the
required matching with high energy QCD. Assuming, in accordance with these
prerequisites, that soft Pomeron intercept is rather large and the slope of the
Pomeron trajectory is equal to zero, we derive analytical formulae that sum
both enhanced and semi-enhanced diagrams for elastic and diffractive
amplitudes. Using parameters obtained from a fit to the available experimental
data, we calculate the Survival Probability for central dijet production at
energies accessible at the LHC. The results presented here which include the
contribution of semi-enhanced and net diagrams, are considerably larger than
our previous estimates.Comment: 11 pages, 10 pictures in .eps file
On The Pomeron at Large 't Hooft Coupling
We begin the process of unitarizing the Pomeron at large 't Hooft coupling.
We do so first in the conformal regime, which applies to good accuracy to a
number of real and toy problems in QCD. We rewrite the conformal Pomeron in the
-plane and transverse position space, and then work out the eikonal
approximation to multiple Pomeron exchange. This is done in the context of a
more general treatment of the complex -plane and the geometric consequences
of conformal invariance. The methods required are direct generalizations of our
previous work on single Pomeron exchange and on multiple graviton exchange in
AdS space, and should form a starting point for other investigations. We
consider unitarity and saturation in the conformal regime, noting elastic and
absorptive effects, and exploring where different processes dominate. Our
methods extend to confining theories and we briefly consider the Pomeron kernel
in this context. Though there is important model dependence that requires
detailed consideration, the eikonal approximation indicates that the Froissart
bound is generically both satisfied and saturated.Comment: 63 pages, 7 figures; published version: references updated and
several typos correcte
The triple-pomeron regime and the structure function of the pomeron in the diffractive deep inelastic scattering at very small x
Misprints and numerical coefficients corrected, a bit of phenomenology and
one figure added. The case for the linear evolution of the unitarized structure
functions made stronger.Comment: KFA-IKP(Th)-1993-17, Landau-16/93, 46 pages, 14 figures upon request
from N.Nikolaev, [email protected]
Shockwaves and deep inelastic scattering within the gauge/gravity duality
Within the gauge/gravity correspondence, we discuss the general formulation
of the shockwave metric which is dual to a 'nucleus' described by the
strongly-coupled N=4 SYM theory in the limit where the number of colors Nc is
arbitrarily large. We emphasize that the 'nucleus' must possess Nc^2 degrees of
freedom per unit volume, so like a finite-temperature plasma, in order for a
supergravity description to exist. We critically reassess previous proposals
for introducing transverse inhomogeneity in the shockwave and formulate a new
proposal in that sense, which involves no external source but requires the
introduction of an 'infrared' cutoff which mimics confinement. This cutoff
however plays no role when the shockwave is probed by a highly virtual
projectile, so like in deep inelastic scattering. We consider two such
projectiles, the dilaton and the R-current, and compute the respective
structure functions including unitarity corrections. We find that there are no
leading-twist contributions to the structure functions at high virtuality,
meaning that there are no point-like constituents in the strongly coupled
'nucleus'. In the black-disk regime at low virtuality, the structure functions
are suggestive of parton saturation with occupation numbers of order one. The
saturation momentum Qs grows with the energy like Qs^2 ~ 1/x (with x the
Bjorken variable), which is the hallmark of graviton exchanges and is also
necessary for the fulfillment of the energy-momentum sum rules.Comment: 43 page
Interactions, Distribution of Pinning Energies, and Transport in the Bose Glass Phase of Vortices in Superconductors
We study the ground state and low energy excitations of vortices pinned to
columnar defects in superconductors, taking into account the long--range
interaction between the fluxons. We consider the ``underfilled'' situation in
the Bose glass phase, where each flux line is attached to one of the defects,
while some pins remain unoccupied. By exploiting an analogy with disordered
semiconductors, we calculate the spatial configurations in the ground state, as
well as the distribution of pinning energies, using a zero--temperature Monte
Carlo algorithm minimizing the total energy with respect to all possible
one--vortex transfers. Intervortex repulsion leads to strong correlations
whenever the London penetration depth exceeds the fluxon spacing. A pronounced
peak appears in the static structure factor for low filling fractions . Interactions lead to a broad Coulomb gap in the distribution of
pinning energies near the chemical potential , separating
the occupied and empty pins. The vanishing of at leads to a
considerable reduction of variable--range hopping vortex transport by
correlated flux line pinning.Comment: 16 pages (twocolumn), revtex, 16 figures not appended, please contact
[email protected]
Epidemic Enhancement in Partially Immune Populations
We observe that a pathogen introduce/pmcdata/journal/plosone/2-2007/1/ingest/pmcmod/sgml/pone.0000165.xmld into a population containing individuals with acquired immunity can result in an epidemic longer in duration and/or larger in size than if the pathogen were introduced into a naive population. We call this phenomenon “epidemic enhancement,” and use simple dynamical models to show that it is a realistic scenario within the parameter ranges of many common infectious diseases. This finding implies that repeated pathogen introduction or intermediate levels of vaccine coverage can lead to pathogen persistence in populations where extinction would otherwise be expected
Odderon in Gauge/String Duality
At high energies, elastic hadronic cross sections, such as , are dominated by vacuum exchange, which in leading order of
the expansion has been identified as the BFKL Pomeron or its strong AdS
dual the closed string Reggeized graviton \cite{Brower:2006ea}. However the
difference of particle anti-particle cross sections are given by a so-called
Odderon, carrying C = -1 vacuum quantum numbers identified in weak coupling
with odd numbers of exchanged gluons. Here we show that in the dual description
the Odderon is the Reggeized Kalb-Ramond field () in the
Neveu-Schwartz sector of closed string theory. To first order in strong
coupling, the high energy contribution of Odderon is evaluated for Super Yang-Mills by a generalization of the gravity dual analysis for
Pomeron in Ref. \cite{Brower:2006ea}. The consequence of confinement on the
Odderon are estimated in the confining QCD-like hardwall model of
Polchinski and Strassler \cite{Polchinski:2001tt}.Comment: 69 pages, 6 figures. Title change to better reflect the content of
the paper. More discussion added in the Comments section. To be published in
JHE
High frequency oscillations during magnetar flares
The recent discovery of high frequency oscillations during giant flares from
the Soft Gamma Repeaters SGR 1806-20 and SGR 1900+14 may be the first direct
detection of vibrations in a neutron star crust. If this interpretation is
correct it offers a novel means of testing the neutron star equation of state,
crustal breaking strain, and magnetic field configuration. We review the
observational data on the magnetar oscillations, including new timing analysis
of the SGR 1806-20 giant flare using data from the Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) and the Rossi X-ray Timing Explorer (RXTE). We
discuss the implications for the study of neutron star structure and crust
thickness, and outline areas for future investigation.Comment: 5 pages, 1 figure, to appear in the proceedings of the conference
"Isolated Neutron Stars: from the Interior to the Surface" (April 2006,
London), eds. D. Page, R. Turolla, & S. Zane, Astrophysics & Space Science in
pres
Martensitic transition and magnetoresistance in a Cu-Al-Mn shape memory alloy. Influence of aging
We have studied the effect of ageing within the miscibility gap on the
electric, magnetic and thermodynamic properties of a non-stoichiometric Heusler
Cu-Al-Mn shape-memory alloy, which undergoes a martensitic transition from a
-based (-phase) towards a close-packed structure (-phase).
Negative magnetoresistance which shows an almost linear dependence on the
square of magnetization with different slopes in the - and -phases,
was observed. This magnetoresistive effect has been associated with the
existence of Mn-rich clusters with the CuAlMn-structure. The effect of an
applied magnetic field on the martensitic transition has also been studied. The
entropy change between the - and -phases shows negligible dependence
on the magnetic field but it decreases significantly with annealing time within
the miscibility gap. Such a decrease is due to the increasing amount of
CuMnAl-rich domains that do not transform martensitically.Comment: 9 pages, 9 figures, accepted for publication in PR
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