146 research outputs found
Results of the Mitrofanoff procedure in urinary tract reconstruction in children
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90139/1/j.1464-410X.1997.33724.x.pd
Exploring improved holographic theories for QCD: Part II
This paper is a continuation of ArXiv:0707.1324 where improved holographic
theories for QCD were set up and explored. Here, the IR confining geometries
are classified and analyzed. They all end in a "good" (repulsive) singularity
in the IR. The glueball spectra are gaped and discrete, and they favorably
compare to the lattice data. Quite generally, confinement and discrete spectra
imply each other. Asymptotically linear glueball masses can also be achieved.
Asymptotic mass ratios of various glueballs with different spin also turn out
to be universal. Mesons dynamics is implemented via space filling D4-anti-D4
brane pairs. The associated tachyon dynamics is analyzed and chiral symmetry
breaking is shown. The dynamics of the RR axion is analyzed, and the
non-perturbative running of the QCD theta-angle is obtained. It is shown to
always vanish in the IR.Comment: 65+18 pages, 20 figures (v3) Some modifications in Appendix E
explaining in more detail the issue of initial conditions; typos corrected.
Published versio
Exploring improved holographic theories for QCD: Part I
Various holographic approaches to QCD in five dimensions are explored using
input both from the putative non-critical string theory as well as QCD. It is
argued that a gravity theory in five dimensions coupled to a dilaton and an
axion may capture the important qualitative features of pure QCD. A part of the
higher alpha' corrections are resummed into a dilaton potential. The potential
is shown to be in one-to-one correspondence with the exact beta-function of
QCD, and its knowledge determines the full structure of the vacuum solution.
The geometry near the UV boundary is that of AdS_5 with logarithmic corrections
reflecting the asymptotic freedom of QCD. We find that all relevant confining
backgrounds have an IR singularity of the "good" kind that allows unambiguous
spectrum computations. Near the singularity the 't Hooft coupling is driven to
infinity. Asymptotically linear glueball masses can also be achieved. The
classification of all confining asymptotics, the associated glueball spectra
and meson dynamics are addressed in a companion paper, ArXiv:0707.1349Comment: 37+23 pages, 11 figures. (v3) Some clarifications and typo
corrections. Journal versio
KK Parity in Warped Extra Dimension
We construct models with a Kaluza-Klein (KK) parity in a five- dimensional
warped geometry, in an attempt to address the little hierarchy problem present
in setups with bulk Standard Model fields. The lightest KK particle (LKP) is
stable and can play the role of dark matter. We consider the possibilities of
gluing two identical slices of 5D AdS in either the UV (IR-UV-IR model) or the
IR region (UV-IR-UV model) and discuss the model-building issues as well as
phenomenological properties in both cases. In particular, we find that the
UV-IR-UV model is not gravitationally stable and that additional mechanisms
might be required in the IR-UV-IR model in order to address flavor issues.
Collider signals of the warped KK parity are different from either the
conventional warped extra dimension without KK parity, in which the new
particles are not necessarily pair-produced, or the KK parity in flat universal
extra dimensions, where each KK level is nearly degenerate in mass. Dark matter
and collider properties of a TeV mass KK Z gauge boson as the LKP are
discussed.Comment: 35 pages, 11 figure
Drag and jet quenching of heavy quarks in a strongly coupled N=2* plasma
The drag of a heavy quark and the jet quenching parameter are studied in the
strongly coupled N=2* plasma using the AdS/CFT correspondence. Both increase in
units of the spatial string tension as the theory departs from conformal
invariance. The description of heavy quark dynamics using a Langevin equation
is also considered. It is found that the difference between the velocity
dependent factors of the transverse and longitudinal momentum broadening of the
quark admit an interpretation in terms of relativistic effects, so the
distribution is spherical in the quark rest frame. When conformal invariance is
broken there is a broadening of the longitudinal momentum distribution. This
effect may be useful in understanding the jet distribution observed in
experiments.Comment: 30 pages, 5 figures, references added, minor corrections. To be
published in JHE
Hard Dense Loops in a Cold Non-Abelian Plasma
Classical transport theory is used to study the response of a non-Abelian
plasma at zero temperature and high chemical potential to weak color
electromagnetic fields. In this article the parallelism between the transport
phenomena occurring in a non-Abelian plasma at high temperature and high
density is stressed. Particularly, it is shown that at high densities it is
also possible to relate the transport equations to the zero-curvature condition
of a Chern-Simons theory in three dimensions, even when quarks are not
considered ultrarelativistic. The induced color current in the cold plasma can
be expressed as an average over angles, which represent the directions of the
velocity vectors of quarks having Fermi energy. From this color current it is
possible to compute -point gluonic amplitudes, with arbitrary . It is
argued that these amplitudes are the same as the ones computed in the high
chemical potential limit of QCD, that are then called hard dense loops. The
agreement between the two different formalisms is checked by computing the
polarization tensor of QED due to finite density effects in the high density
limit.Comment: 16 pages, Revtex, final version to appear in Phys. Rev. D with minor
correction
Critical Behavior of O(n)-symmetric Systems With Reversible Mode-coupling Terms: Stability Against Detailed-balance Violation
We investigate nonequilibrium critical properties of -symmetric models
with reversible mode-coupling terms. Specifically, a variant of the model of
Sasv\'ari, Schwabl, and Sz\'epfalusy is studied, where violation of detailed
balance is incorporated by allowing the order parameter and the dynamically
coupled conserved quantities to be governed by heat baths of different
temperatures and , respectively. Dynamic perturbation theory and the
field-theoretic renormalization group are applied to one-loop order, and yield
two new fixed points in addition to the equilibrium ones. The first one
corresponds to and leads to model A critical
behavior for the order parameter and to anomalous noise correlations for the
generalized angular momenta; the second one is at and is
characterized by mean-field behavior of the conserved quantities, by a dynamic
exponent equal to that of the equilibrium SSS model, and by
modified static critical exponents. However, both these new fixed points are
unstable, and upon approaching the critical point detailed balance is restored,
and the equilibrium static and dynamic critical properties are recovered.Comment: 18 pages, RevTeX, 1 figure included as eps-file; submitted to Phys.
Rev.
On the geometrization of matter by exotic smoothness
In this paper we discuss the question how matter may emerge from space. For
that purpose we consider the smoothness structure of spacetime as underlying
structure for a geometrical model of matter. For a large class of compact
4-manifolds, the elliptic surfaces, one is able to apply the knot surgery of
Fintushel and Stern to change the smoothness structure. The influence of this
surgery to the Einstein-Hilbert action is discussed. Using the Weierstrass
representation, we are able to show that the knotted torus used in knot surgery
is represented by a spinor fulfilling the Dirac equation and leading to a
mass-less Dirac term in the Einstein-Hilbert action. For sufficient complicated
links and knots, there are "connecting tubes" (graph manifolds, torus bundles)
which introduce an action term of a gauge field. Both terms are genuinely
geometrical and characterized by the mean curvature of the components. We also
discuss the gauge group of the theory to be U(1)xSU(2)xSU(3).Comment: 30 pages, 3 figures, svjour style, complete reworking now using
Fintushel-Stern knot surgery of elliptic surfaces, discussion of Lorentz
metric and global hyperbolicity for exotic 4-manifolds added, final version
for publication in Gen. Rel. Grav, small typos errors fixe
Cluster Expansion Approach to the Effective Potential in -Theory
We apply a truncated set of dynamical equations of motion for connected
equal-time Green functions up to the 4-point level to the investigation of
spontaneous ground state symmetry breaking in quantum field
theory. Within our momentum space discretization we obtain a second order phase
transition as soon as the connected 3-point function is included. However, an
additional inclusion of the connected 4-point function still shows a
significant influence on the shape of the effective potential and the critical
coupling.Comment: 1 compressed uuencoded postscript file with 5 figures included, 21
page
Supersymmetric Dark Matter and Yukawa Unification
An analysis of supersymmetric dark matter under the Yukawa unification
constraint is given. The analysis utilizes the recently discovered region of
the parameter space of models with gaugino mass nonuniversalities where large
negative supersymmetric corrections to the b quark mass appear to allow
unification for a positive sign consistent with the and constraints. In the present analysis we use the
revised theoretical determination of ()
in computing the difference which takes account of
a reevaluation of the light by light contribution which has a positive sign.
The analysis shows that the region of the parameter space with
nonuniversalities of the gaugino masses which allows for unification of Yukawa
couplings also contains regions which allow satisfaction of the relic density
constraint. Specifically we find that the lightest neutralino mass consistent
with the relic density constraint, unification for SU(5) and
unification for SO(10) in addition to other constraints lies in the region
below 80 GeV. An analysis of the maximum and the minimum neutralino-proton
scalar cross section for the allowed parameter space including the effect of a
new determination of the pion-nucleon sigma term is also given. It is found
that the full parameter space for this class of models can be explored in the
next generation of proposed dark matter detectors.Comment: 28 pages,nLatex including 5 fig
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