3,617 research outputs found
String Creation, D-branes and Effective Field Theory
This paper addresses several unsettled issues associated with string creation
in systems of orthogonal Dp-D(8-p) branes. The interaction between the branes
can be understood either from the closed string or open string picture. In the
closed string picture it has been noted that the DBI action fails to capture an
extra RR exchange between the branes. We demonstrate how this problem persists
upon lifting to M-theory. These D-brane systems are analysed in the closed
string picture by using gauge-fixed boundary states in a non-standard lightcone
gauge, in which RR exchange can be analysed precisely. The missing piece in the
DBI action also manifests itself in the open string picture as a mismatch
between the Coleman-Weinberg potential obtained from the effective field theory
and the corresponding open string calculation. We show that this difference can
be reconciled by taking into account the superghosts in the (0+1)effective
theory of the chiral fermion, that arises from gauge fixing the spontaneously
broken world-line local supersymmetries.Comment: 33 page
Diboson physics at ATLAS
This paper is intended to give an overview of the ATLAS results on the production cross sections of gauge boson pairs in their fully leptonic decay modes using data from pp collisions at âs = 7TeV for WÎł,ZÎł,WW,ZZ and WZ and âs = 8TeV for ZZ at the Large Hadron Collider. The cross sections are
found to be in agreement with the expectation from the Standard Model within the estimated uncertainties. The production cross section measurements also allow for studies of anomalous triple gauge couplings for which 95% confidence limits are set
Defect flows in minimal models
In this paper we study a simple example of a two-parameter space of
renormalisation group flows of defects in Virasoro minimal models. We use a
combination of exact results, perturbation theory and the truncated conformal
space approach to search for fixed points and investigate their nature. For the
Ising model, we confirm the recent results of Fendley et al. In the case of
central charge close to one, we find six fixed points, five of which we can
identify in terms of known defects and one of which we conjecture is a new
non-trivial conformal defect. We also include several new results on exact
properties of perturbed defects and on the renormalisation group in the
truncated conformal space approach.Comment: 35 pages, 21 figures. 1 reference adde
On supersymmetric interfaces for string theory
We construct the world-sheet interface which preserves space-time
supersymmetry in type II superstring theories in the Green-Schwarz formalism.
This is an analog of the conformal interface in two-dimensional conformal field
theory. We show that a class of the supersymmetric interfaces generates
T-dualities of type II theories, and that these interfaces have a geometrical
interpretation in the doubled target space. We compute the partition function
with a pair of the supersymmetric interfaces inserted, from which we read off
the spectrum of the modes coupled to the interfaces and the Casimir energy
between them. We also derive the transformation rules under which a set of
D-branes is transformed to another by the interface.Comment: 1+23 pages, 1 figure; (v2) added comments, made changes in
presentatio
Effective potential in non-supersymmetric SU(N) x SU(N) gauge theory and interactions of type 0 D3-branes
We study some aspects of short-distance interaction between parallel
D3-branes in type 0 string theory as described by the corresponding
world-volume gauge theory. We compute the one-loop effective potential in the
non-supersymmetric SU(N) x SU(N) gauge theory (which is a Z_2 projection of the
U(2N) n=4 SYM theory) representing dyonic branes composed of N electric and N
magnetic D3-branes. The branes of the same type repel at short distances, but
an electric and a magnetic brane attract, and the forces between self-dual
branes cancel. The self-dual configuration (with the positions of the electric
and the magnetic branes, i.e. the diagonal entries of the adjoint scalar
fields, being the same) is stable against separation of one electric or one
magnetic brane, but is unstable against certain modes of separation of several
same-type branes. This instability should be suppressed in the large N limit,
i.e. should be irrelevant for the large N CFT interpretation of the gauge
theory suggested in hep-th/9901101.Comment: 14 pages, latex, v2: minor corrections, v3: a comment and references
added at the end of section
On running couplings in gauge theories from type-IIB supergravity
We construct an explicit solution of type-IIB supergravity describing the
strong coupling regime of a non-supersymmetric gauge theory. The latter has a
running coupling with an ultraviolet stable fixed point corresponding to the
N=4 SU(N) super-Yang-Mills theory at large N. The running coupling has a power
law behaviour, argued to be universal, that is consistent with holography.
Around the critical point, our solution defines an asymptotic expansion for the
gauge coupling beta-function. We also calculate the first correction to the
Coulombic quark-antiquark potential.Comment: 10 pages, latex, v2: Another form of the solution is given and a
reference is added, v3: a reference is added, final form to appear in PL
Deviations from the Newton law due to extra dimensions
We systematically examine corrections to the gravitational inverse square
law, which are due to compactified extra dimensions. We find the induced
Yukawa-type potentials for which we calculate the strength \alpha and range. In
general the range of the Yukawa correction is given by the wavelength of the
lightest Kaluza-Klein state and its strength, relative to the standard
gravitational potential, by the corresponding degeneracy. In particular, when n
extra dimensions are compactified on an n-torus, we find that the strength of
the potential is \alpha=2n, whereas the compactification on an n-sphere gives
\alpha= n+1. For Calabi-Yau compactifications the strength can be at most
\alpha=20.Comment: 8 pages, latex, 1 figure; v2: References added and some
clarifications in sec. 3 are made; v3: Physics Letters B versio
Maxwell--Chern-Simons gauged non-relativistic O(3) model with self-dual vortices
A non-relativistic version of the 2+1 dimensional gauged Chern-Simons O(3)
sigma model, augmented by a Maxwell term, is presented and shown to support
topologically stable static self-dual vortices. Exactly like their counterparts
of the ungauged model, these vortices are shown to exhibit Hall behaviour in
their dynamics.Comment: 12 pages, LateX, to appear in Mod. Phys. Lett. 199
N=2 Supersymmetric Sigma Models and D-branes
We study D-branes of N=2 supersymmetric sigma models. Supersymmetric
nonlinear sigma models with 2-dimensional target space have D0,D1,D2-branes,
which are realized as A-,B-type supersymmetric boundary conditions on the
worldsheet. When we embed the models in the string theory, the Kahler potential
is restricted and leads to a 2-dim black hole metric with a dilaton background.
The D-branes in this model are susy cycles and consistent with the analysis of
conjugacy classes. The generalized metrics with U(n) isometry is proposed and
dynamics on them are realized by linear sigma models. We investigate D-branes
of the linear sigma models and compare the results with those in the nonlinear
sigma models.Comment: 23 pages, 5 figure
On Heterotic/Type I Duality in d=8
We discuss heterotic corrections to quartic internal U(1) gauge couplings and
check duality by calculating one-loop open string diagrams and identifying the
D-instanton sum in the dual type I picture. We also compute SO(8)^4 threshold
corrections and finally R^2 corrections in type I theory.Comment: 9 pages, Latex, To appear in the proceedings of "Quantum Aspects of
Gauge Theories, Supersymmetries and Unification", Corfu, September 199
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