1,283 research outputs found
Annular Vortex Solutions to the Landau-Ginzburg Equations in Mesoscopic Superconductors
New vortex solutions to the Landau-Ginzburg equations are described. These
configurations, which extend the well known Abrikosov and giant magnetic vortex
ones, consist of a succession of ring-like supercurrent vortices organised in a
concentric pattern, possibly bound to a giant magnetic vortex then lying at
their center. The dynamical and thermodynamic stability of these annular
vortices is an important open issue on which hinges the direct experimental
observation of such configurations. Nevertheless, annular vortices should
affect indirectly specific dynamic properties of mesoscopic superconducting
devices amenable to physical observation.Comment: 12 pages, LaTeX, 2 Postscript figure
Ricci Flow Gravity
A theory of gravitation is proposed, modeled after the notion of a Ricci
flow. In addition to the metric an independent volume enters as a fundamental
geometric structure. Einstein gravity is included as a limiting case. Despite
being a scalar-tensor theory the coupling to matter is different from
Jordan-Brans-Dicke gravity. In particular there is no adjustable coupling
constant. For the solar system the effects of Ricci flow gravity cannot be
distinguished from Einstein gravity and therefore it passes all classical
tests. However for cosmology significant deviations from standard Einstein
cosmology will appear.Comment: 15 pages. V2: improved presentation, in particular Jordan vs.
Brans-Dicke and on viability. Added section on physical interpretation. V3:
more references. Reworked to agree with published versio
Hadronic Contributions to the Muon Anomaly in the Constituent Chiral Quark Model
The hadronic contributions to the anomalous magnetic moment of the muon which
are relevant for the confrontation between theory and experiment at the present
level of accuracy, are evaluated within the same framework: the constituent
chiral quark model. This includes the contributions from the dominant hadronic
vacuum polarization as well as from the next--to--leading order hadronic vacuum
polarization, the contributions from the hadronic light-by-light scattering,
and the contributions from the electroweak hadronic vertex.
They are all evaluated as a function of only one free parameter: the
constituent quark mass. We also comment on the comparison between our results
and other phenomenological evaluations.Comment: Several misprints corrected and a clarifying sentence added. Three
figures superposed and two references added. Version to appear in JHE
On graviton non-Gaussianities during inflation
We consider the most general three point function for gravitational waves
produced during a period of exactly de Sitter expansion. The de Sitter
isometries constrain the possible shapes to only three: two preserving parity
and one violating parity. These isometries imply that these correlation
functions should be conformal invariant. One of the shapes is produced by the
ordinary gravity action. The other shape is produced by a higher derivative
correction and could be as large as the gravity contribution. The parity
violating shape does not contribute to the bispectrum [1106.3228, 1108.0175],
even though it is present in the wavefunction. We also introduce a spinor
helicity formalism to describe de Sitter gravitational waves with circular
polarization. These results also apply to correlation functions in Anti-de
Sitter space. They also describe the general form of stress tensor correlation
functions, in momentum space, in a three dimensional conformal field theory.
Here all three shapes can arise, including the parity violating one.Comment: 51 pages, v2: Corrected statement about parity violation in the
gravitational wave bispectrum. Some other changes and references adde
Weinberg like sum rules revisited
The generalized Weinberg sum rules containing the difference of isovector
vector and axial-vector spectral functions saturated by both finite and
infinite number of narrow resonances are considered. We summarize the status of
these sum rules and analyze their overall agreement with phenomenological
Lagrangians, low-energy relations, parity doubling, hadron string models, and
experimental data.Comment: 31 pages, noticed misprints are corrected, references are added, and
other minor corrections are mad
On Inflation with Non-minimal Coupling
A simple realization of inflation consists of adding the following operators
to the Einstein-Hilbert action: (partial phi)^2, lambda phi^4, and xi phi^2 R,
with xi a large non-minimal coupling. Recently there has been much discussion
as to whether such theories make sense quantum mechanically and if the inflaton
phi can also be the Standard Model Higgs. In this note we answer these
questions. Firstly, for a single scalar phi, we show that the quantum field
theory is well behaved in the pure gravity and kinetic sectors, since the
quantum generated corrections are small. However, the theory likely breaks down
at ~ m_pl / xi due to scattering provided by the self-interacting potential
lambda phi^4. Secondly, we show that the theory changes for multiple scalars
phi with non-minimal coupling xi phi dot phi R, since this introduces
qualitatively new interactions which manifestly generate large quantum
corrections even in the gravity and kinetic sectors, spoiling the theory for
energies > m_pl / xi. Since the Higgs doublet of the Standard Model includes
the Higgs boson and 3 Goldstone bosons, it falls into the latter category and
therefore its validity is manifestly spoiled. We show that these conclusions
hold in both the Jordan and Einstein frames and describe an intuitive analogy
in the form of the pion Lagrangian. We also examine the recent claim that
curvature-squared inflation models fail quantum mechanically. Our work appears
to go beyond the recent discussions.Comment: 14 pages, 2 figures. Version 2: Clarified findings and improved
wording. Elaborated important sections and removed an unnecessary section.
Added references. Version 3: Updated towards JHEP version. Version 4: Final
JHEP versio
Duality Invariant Actions and Generalised Geometry
We construct the non-linear realisation of the semi-direct product of E(11)
and its first fundamental representation at lowest order and appropriate to
spacetime dimensions four to seven. This leads to a non-linear realisation of
the duality groups and introduces fields that depend on a generalised space
which possess a generalised vielbein. We focus on the part of the generalised
space on which the duality groups alone act and construct an invariant action.Comment: 59 pages (typos fixed and added comments
The Overall Coefficient of the Two-loop Superstring Amplitude Using Pure Spinors
Using the results recently obtained for computing integrals over
(non-minimal) pure spinor superspace, we compute the coefficient of the
massless two-loop four-point amplitude from first principles. Contrasting with
the mathematical difficulties in the RNS formalism where unknown normalizations
of chiral determinant formulae force the two-loop coefficient to be determined
only indirectly through factorization, the computation in the pure spinor
formalism can be smoothly carried out.Comment: 29 pages, harvmac TeX. v2: add reference
Supersymmetric QCD: Exact Results and Strong Coupling
We revisit two longstanding puzzles in supersymmetric gauge theories. The
first concerns the question of the holomorphy of the coupling, and related to
this the possible definition of an exact (NSVZ) beta function. The second
concerns instantons in pure gluodynamics, which appear to give sensible, exact
results for certain correlation functions, which nonetheless differ from those
obtained using systematic weak coupling expansions. For the first question, we
extend an earlier proposal of Arkani-Hamed and Murayama, showing that if their
regulated action is written suitably, the holomorphy of the couplings is
manifest, and it is easy to determine the renormalization scheme for which the
NSVZ formula holds. This scheme, however, is seen to be one of an infinite
class of schemes, each leading to an exact beta function; the NSVZ scheme,
while simple, is not selected by any compelling physical consideration. For the
second question, we explain why the instanton computation in the pure
supersymmetric gauge theory is not reliable, even at short distances. The
semiclassical expansion about the instanton is purely formal; if infrared
divergences appear, they spoil arguments based on holomorphy. We demonstrate
that infrared divergences do not occur in the perturbation expansion about the
instanton, but explain that there is no reason to think this captures all
contributions from the sector with unit topological charge. That one expects
additional contributions is illustrated by dilute gas corrections. These are
infrared divergent, and so difficult to define, but if non-zero give order one,
holomorphic, corrections to the leading result. Exploiting an earlier analysis
of Davies et al, we demonstrate that in the theory compactified on a circle of
radius beta, due to infrared effects, finite contributions indeed arise which
are not visible in the formal limit that beta goes to infinity.Comment: 28 pages, two references added, one typo correcte
Dimension-Six Terms in the Standard Model Lagrangian
When the Standard Model is considered as an effective low-energy theory,
higher dimensional interaction terms appear in the Lagrangian. Dimension-six
terms have been enumerated in the classical article by Buchmueller and Wyler
[3]. Although redundance of some of those operators has been already noted in
the literature, no updated complete list has been published to date. Here we
perform their classification once again from the outset. Assuming baryon number
conservation, we find 15 + 19 + 25 = 59 independent operators (barring flavour
structure and Hermitian conjugations), as compared to 16 + 35 + 29 = 80 in
Ref.[3]. The three summed numbers refer to operators containing 0, 2 and 4
fermion fields. If the assumption of baryon number conservation is relaxed, 4
new operators arise in the four-fermion sector.Comment: 16 pages, no figures, v3: Redundant B-violating operator remove
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