1,176 research outputs found
Quantum Isometrodynamics
Classical Isometrodynamics is quantized in the Euclidean plus axial gauge.
The quantization is then generalized to a broad class of gauges and the
generating functional for the Green functions of Quantum Isometrodynamics (QID)
is derived. Feynman rules in covariant Euclidean gauges are determined and QID
is shown to be renormalizable by power counting. Asymptotic states are
discussed and new quantum numbers related to the "inner" degrees of freedom
introduced. The one-loop effective action in a Euclidean background gauge is
formally calculated and shown to be finite and gauge-invariant after
renormalization and a consistent definition of the arising "inner" space
momentum integrals. Pure QID is shown to be asymptotically free for all
dimensions of "inner" space whereas QID coupled to the Standard Model
fields is not asymptotically free for D <= 7. Finally nilpotent BRST
transformations for Isometrodynamics are derived along with the BRST symmetry
of the theory and a scetch of the general proof of renormalizability for QID is
given.Comment: 38 page
Effective Field Theory for the Quantum Electrodynamics of a Graphene Wire
We study the low-energy quantum electrodynamics of electrons and holes, in a
thin graphene wire. We develop an effective field theory (EFT) based on an
expansion in p/p_T, where p_T is the typical momentum of electrons and holes in
the transverse direction, while p are the momenta in the longitudinal
direction. We show that, to the lowest-order in (p/p_T), our EFT theory is
formally equivalent to the exactly solvable Schwinger model. By exploiting such
an analogy, we find that the ground state of the quantum wire contains a
condensate of electron-hole pairs. The excitation spectrum is saturated by
electron-hole collective bound-states, and we calculate the dispersion law of
such modes. We also compute the DC conductivity per unit length at zero
chemical potential and find g_s =e^2/h, where g_s=4 is the degeneracy factor.Comment: 7 pages, 2 figures. Definitive version, accepted for publication on
Phys. Rev.
Fading Gravity and Self-Inflation
We study the cosmology of a toy modified theory of gravity in which gravity
shuts off at short distances, as in the fat graviton scenario of Sundrum. In
the weak-field limit, the theory is perturbatively local, ghost-free and
unitary, although likely suffers from non-perturbative instabilities. We derive
novel self-inflationary solutions from the vacuum equations of the theory,
without invoking scalar fields or other forms of stress energy. The modified
perturbation equation expressed in terms of the Newtonian potential closely
resembles its counterpart for inflaton fluctuations. The resulting scalar
spectrum is therefore slightly red, akin to the simplest scalar-driven
inflationary models. A key difference, however, is that the gravitational wave
spectrum is generically not scale invariant. In particular the tensor spectrum
can have a blue tilt, a distinguishing feature from standard inflation.Comment: 35 pages, 4 figures. v3: version to appear in Phys. Rev.
Gauged supersymmetries in Yang-Mills theory
In this paper we show that Yang-Mills theory in the
Curci-Ferrari-Delbourgo-Jarvis gauge admits some up to now unknown local linear
Ward identities. These identities imply some non-renormalization theorems with
practical simplifications for perturbation theory. We show in particular that
all renormalization factors can be extracted from two-point functions. The Ward
identities are shown to be related to supergauge transformations in the
superfield formalism for Yang-Mills theory. The case of non-zero Curci-Ferrari
mass is also addressed.Comment: 11 pages. Minor changes. Some added reference
Gauge Invariant Treatment of the Electroweak Phase Transition
We evaluate the gauge invariant effective potential for the composite field
in the SU(2)-Higgs model at finite temperature.
Symmetric and broken phases correspond to the domains and
, respectively. The effective potential increases very steeply
at small values of . Predictions for several observables, derived from
the ordinary and the gauge invariant effective potential, are compared. Good
agreement is found for the critical temperature and the jump in the order
parameter. The results for the latent heat differ significantly for large Higgs
masses.Comment: 8 pages latex, DESY-94-043, 4 figures can be obtained via e-mail from
[email protected]
Breakdown of the perturbative renormalization group at certain quantum critical points
It is shown that the presence of multiple time scales at a quantum critical
point can lead to a breakdown of the loop expansion for critical exponents,
since coefficients in the expansion diverge. Consequently, results obtained
from finite-order perturbative renormalization-group treatments may be not be
an approximation in any sense to the true asymptotic critical behavior. This
problem manifests itself as a non-renormalizable field theory, or,
equivalently, as the presence of a dangerous irrelevant variable. The quantum
ferromagnetic transition in disordered metals provides an example.Comment: 4pp, 1 eps fi
The Effect of Interactions on the Conductance of Graphene Nanoribbons
We study the effects of the interaction between electrons and holes on the
conductance G of quasi-one-dimensional graphene systems.
We first consider as a benchmark the limit in which all interactions are
negligible, recovering the predictions of the tight-binding approximation for
the spectrum of the system, and the well-known result G=4 e^2/h for the lowest
conductance quantum. Then we consider an exactly solvable field theoretical
model in which the electro-magnetic interactions are effectively local.
Finally, we use the effective field theory formalism to develop an exactly
solvable model in which we also include the effect of non-local interactions.
We find that such interactions turn the nominally metallic armchair graphene
nanoribbon into a semi-conductor, while the short-range interactions lead to a
correction to the G=4 e^2/h formula.Comment: 9 pages, 1 figur
Critical behavior of supersymmetric O(N) models in the large-N limit
We derive a supersymmetric renormalization group (RG) equation for the
scale-dependent superpotential of the supersymmetric O(N) model in three
dimensions. For a supersymmetric optimized regulator function we solve the RG
equation for the superpotential exactly in the large-N limit. The fixed-point
solutions are classified by an exactly marginal coupling. In the weakly coupled
regime there exists a unique fixed point solution, for intermediate couplings
we find two separate fixed point solutions and in the strong coupling regime no
globally defined fixed-point potentials exist. We determine the exact critical
exponents both for the superpotential and the associated scalar potential.
Finally we relate the high-temperature limit of the four-dimensional theory to
the Wilson-Fisher fixed point of the purely scalar theory.Comment: 13 pages,4 figure
Regularization Methods in Chiral Perturbation Theory
Chiral lagrangians describing the interactions of Goldstone bosons in a
theory possessing spontaneous symmetry breaking are effective,
non-renormalizable field theories in four dimensions. Yet, in a momentum
expansion one is able to extract definite, testable predictions from
perturbation theory. These techniques have yielded in recent years a wealth of
information on many problems where the physics of Goldstone bosons plays a
crucial role, but theoretical issues concerning chiral perturbation theory
remain, to this date, poorly treated in the literature. We present here a
rather comprehensive analysis of the regularization and renormalization
ambiguities appearing in chiral perturbation theory at the one loop level. We
discuss first on the relevance of dealing with tadpoles properly. We
demonstrate that Ward identities severely constrain the choice of regulators to
the point of enforcing unique, unambiguous results in chiral perturbation
theory at the one-loop level for any observable which is renormalization-group
invariant. We comment on the physical implications of these results and on
several possible regulating methods that may be of use for some applications.Comment: 37 pages, 5 figs. not included (available upon request), LaTeX,
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