787 research outputs found
The a-theorem and conformal symmetry breaking in holographic RG flows
We study holographic models describing an RG flow between two fixed points
driven by a relevant scalar operator. We show how to introduce a spurion field
to restore Weyl invariance and compute the anomalous contribution to the
generating functional in even dimensional theories. We find that the
coefficient of the anomalous term is proportional to the difference of the
conformal anomalies of the UV and IR fixed points, as expected from anomaly
matching arguments in field theory. For any even dimensions the coefficient is
positive as implied by the holographic a-theorem. For flows corresponding to
spontaneous breaking of conformal invariance, we also compute the two-point
functions of the energy-momentum tensor and the scalar operator and identify
the dilaton mode. Surprisingly we find that in the simplest models with just
one scalar field there is no dilaton pole in the two-point function of the
scalar operator but a stronger singularity. We discuss the possible
implications.Comment: 50 pages. v2: minor changes, added references, extended discussion.
v3: we have clarified some of the calculations and assumptions, results
unchanged. v4: published version in JHE
Explicit de Sitter Flux Vacua for Global String Models with Chiral Matter
We address the open question of performing an explicit stabilisation of all
closed string moduli (including dilaton, complex structure and Kaehler moduli)
in fluxed type IIB Calabi-Yau compactifications with chiral matter. Using toric
geometry we construct Calabi-Yau manifolds with del Pezzo singularities.
D-branes located at such singularities can support the Standard Model gauge
group and matter content. In order to control complex structure moduli
stabilisation we consider Calabi-Yau manifolds which exhibit a discrete
symmetry that reduces the effective number of complex structure moduli. We
calculate the corresponding periods in the symplectic basis of invariant
three-cycles and find explicit flux vacua for concrete examples. We compute the
values of the flux superpotential and the string coupling at these vacua.
Starting from these explicit complex structure solutions, we obtain AdS and dS
minima where the Kaehler moduli are stabilised by a mixture of D-terms,
non-perturbative and perturbative alpha'-corrections as in the LARGE Volume
Scenario. In the considered example the visible sector lives at a dP_6
singularity which can be higgsed to the phenomenologically interesting class of
models at the dP_3 singularity.Comment: 49 pages, 5 figures; v2: references adde
Superstring Theory and CP- Violating Phases: Can They Be Related?
We investigate the possibility of large CP- violating phases in the soft
breaking terms derived in superstring models. The bounds on the electric dipole
moments (EDM's) of the electron and neutron are satisfied through cancellations
occuring because of the structure of the string models. Three general classes
of four-dimensional string models are considered: (i) orbifold
compactifications of perturbative heterotic string theory, (ii) scenarios based
on Ho\v{r}ava-Witten theory, and (iii) Type I string models (Type IIB
orientifolds). Nonuniversal phases of the gaugino mass parameters greatly
facilitate the necessary cancellations among the various contributions to the
EDM's; in the overall modulus limit, the gaugino masses are universal at tree
level in both the perturbative heterotic models and the Ho\v{r}ava-Witten
scenarios, which severely restricts the allowed regions of parameter space.
Nonuniversal gaugino masses do arise at one-loop in the heterotic orbifold
models, providing for corners of parameter space with phases
consistent with the phenomenological bounds. However, there is a possibility of
nonuniversal gaugino masses at tree level in the Type I models, depending on
the details of the embedding of the SM into the D- brane sectors. We find that
in a minimal model with a particular embedding of the Standard Model gauge
group into two D- brane sectors, viable large phase solutions can be obtained
over a wide range of parameter space.Comment: 28 pages, 6 figures; corrected bug in the code and a few typos,
results qualitatively unchange
Real Time QRS Detection Based on M-ary Likelihood Ratio Test on the DFT Coefficients
This paper shows an adaptive statistical test for QRS detection of electrocardiography (ECG) signals. The method is based on a M-ary generalized likelihood ratio test (LRT) defined over a multiple observation window in the Fourier domain. The motivations for proposing another detection algorithm based on maximum a posteriori (MAP) estimation are found in the high complexity of the signal model proposed in previous approaches which i) makes them computationally unfeasible or not intended for real time applications such as intensive care monitoring and (ii) in which the parameter selection conditions the overall performance. In this sense, we propose an alternative model based on the independent Gaussian properties of the Discrete Fourier Transform (DFT) coefficients, which allows to define a simplified MAP probability function. In addition, the proposed approach defines an adaptive MAP statistical test in which a global hypothesis is defined on particular hypotheses of the multiple observation window. In this sense, the observation interval is modeled as a discontinuous transmission discrete-time stochastic process avoiding the inclusion of parameters that constraint the morphology of the QRS complexes.This work has received research funding from the Spanish government (www.micinn.es) under project TEC2012 34306 (DiagnoSIS, Diagnosis by means of Statistical Intelligent Systems, 70K€) and projects P09-TIC-4530 (300K€) and P11-TIC-7103 (156K€) from the Andalusian government (http://www.juntadeandalucia.es/organismos/economiainnovacioncienciayempleo.html)
Exclusive Photoproduction of the Cascade (Xi) Hyperons
We report on the first measurement of exclusive Xi-(1321) hyperon
photoproduction in gamma p --> K+ K+ Xi- for 3.2 < E(gamma) < 3.9 GeV. The
final state is identified by the missing mass in p(gamma,K+ K+)X measured with
the CLAS detector at Jefferson Laboratory. We have detected a significant
number of the ground-state Xi-(1321)1/2+, and have estimated the total cross
section for its production. We have also observed the first excited state
Xi-(1530)3/2+. Photoproduction provides a copious source of Xi's. We discuss
the possibilities of a search for the recently proposed Xi5-- and Xi5+
pentaquarks.Comment: submitted to Phys. Rev.
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Reply to J.J. Muñoz-Perez et al. Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SWSpain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)
In a novel finding for a beach environment, Poizot
et al. (2013) identified an FB+ trend (sediments becoming
finer, better sorted and more positively skewed upshore) on a
well-developed swash bar on the upper foreshore of the
Camposoto beach of Cádiz in SW Spain. In their Discussion
of that paper, Muñoz-Perez et al. (2014) provide some
supporting arguments and also report grain-size, beach profile
and other data from nearby beaches which differ from those of
Poizot and colleagues for Camposoto beach, pointing out that
a trend observed on one beach may not apply to a
neighbouring beach. However, even though the absolute
values differ, the overall trends actually do show the same
general behaviour. In our Reply to their comments, we also
address some difficulties in comparing granulometric datasets
generated by different analytical techniques
Radial variation of attenuation and star formation in the largest late-type disks observed with GALEX
For a sample of 43 nearby, late-type galaxies, we have investigated the
radial variation of both the current star formation rate and the dust-induced
UV light attenuation. To do this we have cross-correlated IRAS images and GALEX
observations for each of these galaxies, and compiled observations of the gas
(CO and HI) and metal-abundance gradients found in the literature. We find that
attenuation correlates with metallicity. We then use the UV profiles, corrected
for attenuation, to study several variants of the Schmidt law and conclude that
our results are compatible with a simple law similar to the one of Kennicutt
but extending smoothly to lower surface densities, but with considerable
scatter. We do not detect an abrupt break in the UV light at the threshold
radius derived from H-alpha data (at which the H-alpha profile shows a break
and beyond which only a few HII regions are usually found). We interpret the
H-alpha sudden break not as a change in the star formation regime (as often
suggested) but as the vanishingly small number of ionizing stars corresponding
to low levels of star formation.Comment: 28 pages, 9 figures, accepted for the GALEX special issue of ApJS.
For a version with high-resolution figures, see
http://www.oamp.fr/boissier/preprint/preprint.htm
Two-point functions in a holographic Kondo model
We develop the formalism of holographic renormalization to compute two-point
functions in a holographic Kondo model. The model describes a
-dimensional impurity spin of a gauged interacting with a
-dimensional, large-, strongly-coupled Conformal Field Theory (CFT).
We describe the impurity using Abrikosov pseudo-fermions, and define an
-invariant scalar operator \mathcalO built from a pseudo-fermion and
a CFT fermion. At large the Kondo interaction is of the form
\mathcalO^\dagger \mathcalO, which is marginally relevant, and
generates a Renormalization Group (RG) flow at the impurity. A second-order
mean-field phase transition occurs in which \mathcalO condenses below a
critical temperature, leading to the Kondo effect, including screening of the
impurity. Via holography, the phase transition is dual to holographic
superconductivity in -dimensional Anti-de Sitter space. At all
temperatures, spectral functions of \mathcalO exhibit a Fano resonance,
characteristic of a continuum of states interacting with an isolated resonance.
In contrast to Fano resonances observed for example in quantum dots, our
continuum and resonance arise from a -dimensional UV fixed point and RG
flow, respectively. In the low-temperature phase, the resonance comes from a
pole in the Green's function of the form , which
is characteristic of a Kondo resonance
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