1,712 research outputs found
The Effect of Gravitational Tidal Forces on Vacuum Polarization: How to Undress a Photon
The effect of gravitational tidal forces on photon propagation in curved
spacetime is investigated. It is found that the imaginary part of the local
refractive index Im n(u;w) may be negative as well as positive, corresponding
to a local amplification as well as attenuation of the amplitude of the
renormalized photon field. This is interpreted in terms of the effect of tidal
forces on the virtual e^+e^- cloud surrounding the bare photon field---a
positive/negative Im n(u;w) corresponds to an increased dressing/undressing of
the bare photon. Below threshold decays of the photon to e^+e^- pairs can
occur. Photon undressing in the vicinity of a black hole singularity is
described as an example. These results are shown to be consistent with
unitarity and the optical theorem in curved spacetime, which is derived here
both in a local form and integrated over the photon trajectory.Comment: 13 pages, 1 figure, minor correction
The Unbearable Beingness of Light, Dressing and Undressing Photons in Black Hole Spacetimes
Gravitational tidal forces acting on the virtual e+ e- cloud surrounding a
photon endow spacetime with a non-trivial refractive index. This has remarkable
properties unique to gravitational theories including superluminal
low-frequency propagation, in apparent violation of causality, and
amplification of the renormalized photon field, in apparent violation of
unitarity. Using the geometry of null congruences and the Penrose limit, we
illustrate these phenomena and their resolution by tracing the history of a
photon as it falls into the near-singularity region of a black hole.Comment: 8 pages, Essay awarded third prize in the Gravity Research Foundation
essay competition 201
Graviton Propagation and Vacuum Polarization in Curved Space
The effects of vacuum polarization arising from loops of massive scalar
particles on graviton propagation in curved space are considered. Physically,
they are due to curvature induced tidal forces acting on the cloud of virtual
scalar particles surrounding the graviton. The effects are tractable in a WKB
and large mass limit and the results can be written as an effective refractive
index for the graviton modes with both a real and imaginary part. The imaginary
part of the refractive index is a curvature induced contribution to the
wavefunction renormalization of the graviton in real affine time and can have
the effect of dressing or un-dressing the graviton. The real part of the
refractive index increases logarithmically at high frequency as long as the
null energy condition is satisfied by the background.Comment: 21 pages, typos correcte
Instantons, finite N=2 Sp(N) theories and the AdS/CFT correspondence
We examine ADHM multi-instantons in the conformal N=2 supersymmetric Sp(N)
gauge theory with one anti-symmetric tensor and four fundamental
hypermultiplets. We argue that the ADHM construction and measure can also be
deduced from purely field theoretic considerations and also from the dynamics
of D-instantons in the presence of D3-branes, D7-branes and an orientifold
O7-plane. The measure then admits a large-N saddle-point approximation where
the D3-branes disappear but the background is changed to AdS_5 x S^5/Z_2, as
expected on the basis of the AdS/CFT correspondence. The large-N measure
displays the fractionation of D-instantons at the singularity S^3 in S^5/Z_2
and is described for instanton number k by a certain O(k) matrix model.Comment: 16 pages, jhep.cl
Semi-classical decay of monopoles in N=2 gauge theory
It is shown how monopoles and dyons decay on curves of marginal stability in
the moduli space of vacua at weak coupling in pure N=2 gauge theory with
arbitrary gauge group. The analysis involves a semi-classical treatment of the
monopole and rests on the fact that the monopole moduli space spaces for a
magnetic charge vector equal to a non-simple root enlarge discontinuously at
the curves of marginal stability. This enlargement of the moduli space
describes the freedom for the monopole to be separated into stable constituent
monopoles. Such decays do not occur in the associated theory with N=4
supersymmetry because in this case there exist bound-states at threshold.Comment: 17 pages, plain tex with macro included. Minor changes, more
references include
Quantizing SL(N) Solitons and the Hecke Alegbra
The problem of quantizing a class of two-dimensional integrable quantum field
theories is considered. The classical equations of the theory are the complex
affine Toda equations which admit soliton solutions with real masses.
The classical scattering theory of the solitons is developed using Hirota's
solution techniques. A form for the soliton -matrix is proposed based on the
constraints of -matrix theory, integrability and the requirement that the
semi-classical limit is consistent with the semi-classical WKB quantization of
the classical scattering theory. The proposed -matrix is an intertwiner of
the quantum group associated to , where the deformation parameter is a
function of the coupling constant. It is further shown that the -matrix
describes a non-unitary theory, which reflects the fact that the classical
Hamiltonian is complex. The spectrum of the theory is found to consist of the
basic solitons, scalar states (or breathers) and excited (or `breathing')
solitons. It is also noted that the construction of the -matrix is valid for
any representation of the Hecke algebra, allowing the definition of restricted
-matrices, in which case the theory is unitary.Comment: 35 page
Strong Coupling N=2 Gauge Theory with Arbitrary Gauge Group
A complete definition of the cycles, on the auxiliary Riemann surface defined
by Martinec and Warner for describing pure N=2 gauge theories with arbitrary
group, is provided. The strong coupling monodromies around the vanishing cycles
are shown to arise from a set of dyons which becomes massless at the
singularities. It is shown how the correct weak coupling monodromies are
reproduced and how the dyons have charges which are consistent with the
spectrum that can be calculated at weak coupling using conventional
semi-classical methods. In particular, the magnetic charges are co-root vectors
as required by the Dirac-Schwinger-Zwanziger quantization condition.Comment: 18 Pages, Latex (amstex package), 4 figures included with eps
The exact mass-gaps of the principal chiral models
An exact expression for the mass-gap, the ratio of the physical particle mass
to the -parameter, is found for the principal chiral sigma models
associated to all the classical Lie algebras. The calculation is based on a
comparison of the free-energy in the presence of a source coupling to a
conserved charge of the theory computed in two ways: via the thermodynamic
Bethe Ansatz from the exact scattering matrix and directly in perturbation
theory. The calculation provides a non-trivial test of the form of the exact
scattering matrix.Comment: 11 pages, (macro included), CERN-TH.7164/94, SWAT/93-94/2
On the Coulomb Branch of a Marginal Deformation of N=4 SUSY Yang-Mills
We determine the exact vacuum structure of a marginal deformation of N=4 SUSY
Yang-Mills with gauge group U(N). The Coulomb branch of the theory consists of
several sub-branches which are governed by complex curves of the form
Sigma_{n_{1}} U Sigma_{n_{2}} U Sigma_{n_{3}} of genus N=n_{1}+n_{2}+n_{3}.
Each sub-branch intersects with a family of Higgs and Confining branches
permuted by SL(2,Z) transformations. We determine the curve by solving a
related matrix model in the planar limit according to the prescription of
Dijkgraaf and Vafa, and also by explicit instanton calculations using a form of
localization on the instanton moduli space. We find that Sigma_{n} coincides
with the spectral curve of the n-body Ruijsenaars-Schneider system. Our results
imply that the theory on each sub-branch is holomorphically equivalent to
certain five-dimensional gauge theory with eight supercharges. This equivalence
also implies the existence of novel confining branches in five dimensions.Comment: LaTeX file. 48 page
Vacua of N=1 Supersymmetric QCD from Spin Chains and Matrix Models
We consider the vacuum structure of the finite N=2 theory with N_f=2N
fundamental hypermultiplets broken to N=1 by a superpotential for the adjoint
chiral multiplet. We do this in two ways: firstly, by compactification to three
dimensions, in which case the effective superpotential is the Hamiltonian of an
integrable spin chain. In the second approach, we consider the Dijkgraaf-Vafa
holomorphic matrix model. We prove that the two approaches agree as long as the
couplings of the two theories are related in a particular way involving an
infinite series of instanton terms. The case of gauge group SU(2) with N_f=4 is
considered in greater detail.Comment: 28 pages, 2 figure
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