86 research outputs found
On the equivalence between Implicit Regularization and Constrained Differential Renormalization
Constrained Differential Renormalization (CDR) and the constrained version of
Implicit Regularization (IR) are two regularization independent techniques that
do not rely on dimensional continuation of the space-time. These two methods
which have rather distinct basis have been successfully applied to several
calculations which show that they can be trusted as practical, symmetry
invariant frameworks (gauge and supersymmetry included) in perturbative
computations even beyond one-loop order.
In this paper, we show the equivalence between these two methods at one-loop
order. We show that the configuration space rules of CDR can be mapped into the
momentum space procedures of Implicit Regularization, the major principle
behind this equivalence being the extension of the properties of regular
distributions to the regularized ones.Comment: 16 page
Differential Equations for Definition and Evaluation of Feynman Integrals
It is shown that every Feynman integral can be interpreted as Green function
of some linear differential operator with constant coefficients. This
definition is equivalent to usual one but needs no regularization and
application of -operation. It is argued that presented formalism is
convenient for practical calculations of Feynman integrals.Comment: pages, LaTEX, MSU-PHYS-HEP-Lu2/9
Defect Conformal Field Theory and Locally Localized Gravity
Gravity may be "locally localized" over a wide range of length scales on a
d-dimensional anti-de Sitter (AdS) brane living inside AdS_{d+1}. In this paper
we examine this phenomenon from the point of view of the holographic dual
"defect conformal field theory". The mode expansion of bulk fields on the
gravity side is shown to be precisely dual to the "boundary operator product
expansion" of operators as they approach the defect. From the field theory
point of view, the condition for localization is that a "reduced operator"
appearing in this expansion acquires negative anomalous dimension. In
particular, a very light localized graviton exists when a mode arising from the
reduction of the ambient stress-energy tensor to the defect has conformal
dimension Delta ~ d-1. The part of the stress tensor containing the defect
dynamics has dimension Delta = d-1 in the free theory, but we argue that it
acquires an anomalous dimension in the interacting theory, and hence does not
participate in localization in the regime of small backreaction of the brane.
We demonstrate that such an anomalous dimension is consistent with the
conservation of the full stress-energy tensor. Finally, we analyze how to
compute the anomalous dimensions of reduced operators from gravity at leading
order in the interactions with the brane.Comment: 38 pages, LaTeX, 5 figures. v2: typos fixe
Instant preheating mechanism and UHECR
Top-down models assume that the still unexplained Ultra High Energy Cosmic
Rays (UHECR's) are the decay products of superheavy particles. Such particles
may have been produced by one of the post-inflationary reheating mechanisms and
may account for a fraction of the cold dark matter. In this paper, we assess
the phenomenological applicability of the simplest instant preheating framework
not to describe a reheating process, but as a mechanism to generate relic
supermassive particles as possible sources of UHECR's. We use cosmic ray flux
and cold dark matter observational data to constrain the parameters of the
model.Comment: 7 pages, 2 figures, submitted to PR
Anomalies, Anomalous U(1)'s and generalized Chern-Simons terms
A detailed analysis of anomalous U(1)'s and their effective couplings is
performed both in field theory and string theory. It is motivated by the
possible relevance of such couplings in particle physics, as well as a
potential signal distinguishing string theory from other UV options. The most
general anomaly related effective action is analyzed and parameterized. It
contains Stuckelberg, axionic and Chern-Simons-like couplings. It is shown that
such couplings are generically non-trivial in orientifold string vacua and are
not in general fixed by anomalies. A similar analysis in quantum field theories
provides similar couplings. The trilinear gauge boson couplings are also
calculated and their phenomenological relevance is advocated. We do not find
qualitative differences between string and field theory in this sector.Comment: 52 pages, 2 eps figures, LaTeX, feynmf & youngtab packages (v2 -
Minor corrections, references added
Thick de Sitter 3-Branes, Dynamic Black Holes and Localization of Gravity
The embedding of a thick de Sitter 3-brane into a five-dimensional bulk is
studied, assuming a scalar field with potential is present in the bulk. A class
of solutions is found in closed form that can represent a thick de Sitter
3-brane interpolating either between two dynamical black holes with a topology or between two Rindler-like spacetimes with a topology. The gravitational field is localized in a small region near
the center of the 3-brane. The analysis of graviton fluctuations shows that a
zero mode exists and separates itself from a set of continuous modes by a mass
gap. The existence of such a mass gap is shown to be universal. The scalar
perturbations are also studied and shown to be stable.Comment: the study of scalar perturbations and some relevant references have
been added. The most used definition for mass in de Sitter space has been
adopte
Integrable twists in AdS/CFT
A class of marginal deformations of four-dimensional N=4 super Yang-Mills
theory has been found to correspond to a set of smooth, multiparameter
deformations of the S^5 target subspace in the holographic dual on AdS_5 x S^5.
We present here an analogous set of deformations that act on global toroidal
isometries in the AdS_5 subspace. Remarkably, certain sectors of the string
theory remain classically integrable in this larger class of so-called
gamma-deformed AdS_5 x S^5 backgrounds. Relying on studies of deformed
su(2)_gamma models, we formulate a local sl(2)_gamma Lax representation that
admits a classical, thermodynamic Bethe equation (based on the Riemann-Hilbert
interpretation of Bethe's ansatz) encoding the spectrum in the deformed AdS_5
geometry. This result is extended to a set of discretized, asymptotic Bethe
equations for the twisted string theory. Near-pp-wave energy spectra within
sl(2)_gamma and su(2)_gamma sectors provide a useful and stringent test of such
equations, demonstrating the reliability of this technology in a wider class of
string backgrounds. In addition, we study a twisted Hubbard model that yields
certain predictions of the dual beta-deformed gauge theory.Comment: v2: references and clarifications added, 46 page
Perturbative QCD and factorization of coherent pion photoproduction on the deuteron
We analyze the predictions of perturbative QCD for pion photoproduction on
the deuteron, gamma D -> pi^0 D, at large momentum transfer using the reduced
amplitude formalism. The cluster decomposition of the deuteron wave function at
small binding only allows the nuclear coherent process to proceed if each
nucleon absorbs an equal fraction of the overall momentum transfer.
Furthermore, each nucleon must scatter while remaining close to its mass shell.
Thus the nuclear photoproduction amplitude, M_{gamma D -> pi^0 D}(u,t),
factorizes as a product of three factors: (1) the nucleon photoproduction
amplitude, M_{gamma N_1 -> pi^0 N_1}(u/4,t/4), at half of the overall momentum
transfer, (2) a nucleon form factor, F_{N_2}(t/4), at half the overall momentum
transfer, and (3) the reduced deuteron form factor, f_d(t), which according to
perturbative QCD, has the same monopole falloff as a meson form factor. A
comparison with the recent JLAB data for gamma D -> pi^0 D of Meekins et al.
[Phys. Rev. C 60, 052201 (1999)] and the available gamma p -> pi^0 p data shows
good agreement between the perturbative QCD prediction and experiment over a
large range of momentum transfers and center of mass angles. The reduced
amplitude prediction is consistent with the constituent counting rule, p^11_T
M_{gamma D -> pi^0 D} -> F(theta_cm), at large momentum transfer. This is found
to be consistent with measurements for photon lab energies E_gamma > 3 GeV at
theta_cm=90 degrees and \elab > 10 GeV at 136 degrees.Comment: RevTeX 3.1, 17 pages, 6 figures; v2: incorporates minor changes as
version accepted by Phys Rev
Slepton and Neutralino/Chargino Coannihilations in MSSM
Within the low-energy effective Minimal Supersymmetric extension of Standard
Model (effMSSM) we calculated the neutralino relic density taking into account
slepton-neutralino and neutralino-chargino/neutralino coannihilation channels.
We performed comparative study of these channels and obtained that both of them
give sizable contributions to the reduction of the relic density. Due to these
coannihilation processes some models (mostly with large neutralino masses)
enter into the cosmologically interesting region for relic density, but other
models leave this region. Nevertheless, in general, the predictions for direct
and indirect dark matter detection rates are not strongly affected by these
coannihilation channels in the effMSSM.Comment: 12 pages, 9 figures, revte
Rotating Strings with Two Unequal Spins in Lunin-Maldacena Background
We study a string motion in the Lunin-Maldacena background, that is, the
\beta-deformed AdS_5 \times \tilde{S}^5 background dual to a \beta-deformation
of \mathcal{N} = 4 super Yang-Mills theory. For real \beta we construct a
rotating and wound string solution which has two unequal spins in \tilde{S}^5.
The string energy is expressed in terms of the spins, the winding numbers and
the deformation parameter. In the expansion of \lambda/J^2 with the total spin
J and the string tension \sqrt{\lambda} we present ``one-loop" and ``two-loop"
energy corrections. The ``one-loop" one agrees with the one-loop anomalous
dimension of the corresponding gauge-theory scalar operators obtained in
hep-th/0503192 from the \beta-deformed Bethe equation as well as the
anisotropic Landau-Lifshitz equation.Comment: 13 pages, LaTeX, no figure
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