3,164 research outputs found
Flux-induced Soft Terms on Type IIB/F-theory Matter Curves and Hypercharge Dependent Scalar Masses
Closed string fluxes induce generically SUSY-breaking soft terms on
supersymmetric type IIB orientifold compactifications with D3/D7 branes. This
was studied in the past by inserting those fluxes on the DBI+CS actions for
adjoint D3/D7 fields, where D7-branes had no magnetic fluxes. In the present
work we generalise those computations to the phenomenologically more relevant
case of chiral bi-fundamental fields laying at 7-brane intersections and
F-theory local matter curves. We also include the effect of 7-brane magnetic
flux as well as more general closed string backgrounds, including the effect of
distant (anti-)D3-branes. We discuss several applications of our results. We
find that squark/slepton masses become in general flux-dependent in F-theory
GUT's. Hypercharge-dependent non-universal scalar masses with a characteristic
sfermion hierarchy m_E^2 < m_L^2 < m_Q^2 < m_D^2 < m_U^2 are obtained. There
are also flavor-violating soft terms both for matter fields living at
intersecting 7-branes or on D3-branes at singularities. They point at a very
heavy sfermion spectrum to avoid FCNC constraints. We also discuss the possible
microscopic description of the fine-tuning of the EW Higgs boson in
compactifications with a MSSM spectrum.Comment: 67 pages, 2 figures, 2 table
Measuring the interaction force between a high temperature superconductor and a permanent magnet
Repulsive and attractive forces are both possible between a superconducting
sample and a permanent magnet, and they can give place to magnetic levitation
or free-suspension phenomena, respectively. We show experiments to quantify
this magnetic interaction which represents a promising field regarding to
short-term technological applications of high temperature superconductors. The
measuring technique employs an electronic balance and a rare-earth magnet that
induces a magnetic moment in a melt-textured YBa2Cu3O7 superconductor immersed
in liquid nitrogen. The simple design of the experiments allows a fast and easy
implementation in the advanced physics laboratory with a minimum cost. Actual
levitation and suspension demonstrations can be done simultaneously as a help
to interpret magnetic force measurements.Comment: 12 pages and 3 figures in postscrip
Optical conductivity and Raman scattering of iron superconductors
We discuss how to analyze the optical conductivity and Raman spectra of
multi-orbital systems using the velocity and the Raman vertices in a similar
way Raman vertices were used to disentangle nodal and antinodal regions in
cuprates. We apply this method to iron superconductors in the magnetic and
non-magnetic states, studied at the mean field level. We find that the
anisotropy in the optical conductivity at low frequencies reflects the
difference between the magnetic gaps at the X and Y electron pockets. Both gaps
are sampled by Raman spectroscopy. We also show that the Drude weight
anisotropy in the magnetic state is sensitive to small changes in the lattice
structure.Comment: 14 pages, 10 figures, as accepted in Phys. Rev. B,
explanations/discussion added in Secs. II, III and V
Higgs-otic Inflation and Moduli Stabilization
We study closed-string moduli stabilization in Higgs-otic inflation in Type
IIB orientifold backgrounds with fluxes. In this setup large-field inflation is
driven by the vacuum energy of mobile D7-branes. Imaginary selfdual (ISD)
three-form fluxes in the background source a -term and the necessary
monodromy for large field excursions while imaginary anti-selfdual (IASD)
three-form fluxes are sourced by non-perturbative contributions to the
superpotential necessary for moduli stabilization. We analyze K\"ahler moduli
stabilization and backreaction on the inflaton potential in detail. Confirming
results in the recent literature, we find that integrating out heavy K\"ahler
moduli leads to a controlled flattening of the inflaton potential. We quantify
the flux tuning necessary for stability even during large-field inflation.
Moreover, we study the backreaction of supersymmetrically stabilized complex
structure moduli and the axio-dilaton in the K\"ahler metric of the inflaton.
Contrary to previous findings, this backreaction can be pushed far out in field
space if a similar flux tuning as in the K\"ahler sector is possible. This
allows for a trans-Planckian field range large enough to support inflation.Comment: 42 pages, 10 figures, v2: comments and references added. Published
versio
The DBI Action, Higher-derivative Supergravity, and Flattening Inflaton Potentials
In string theory compactifications it is common to find an effective
Lagrangian for the scalar fields with a non-canonical kinetic term. We study
the effective action of the scalar position moduli of Type II D-branes. In
many instances the kinetic terms are in fact modified by a term proportional to
the scalar potential itself. This can be linked to the appearance of
higher-dimensional supersymmetric operators correcting the K\"ahler potential.
We identify the supersymmetric dimension-eight operators describing the
corrections captured by the D-brane Dirac-Born-Infeld action. Our
analysis then allows an embedding of the D-brane moduli effective action into
an supergravity formulation. The effects of the
potential-dependent kinetic terms may be very important if one of the scalars
is the inflaton, since they lead to a flattening of the scalar potential. We
analyze this flattening effect in detail and compute its impact on the CMB
observables for single-field inflation with monomial potentials.Comment: 25 pages, 3 figures. Comments and references added. Published versio
Searching for tidal tails around Centauri using RR Lyrae Stars
We present a survey for RR Lyrae stars in an area of 50 deg around the
globular cluster Centauri, aimed to detect debris material from the
alleged progenitor galaxy of the cluster. We detected 48 RR Lyrae stars of
which only 11 have been previously reported. Ten among the eleven previously
known stars were found inside the tidal radius of the cluster. The rest were
located outside the tidal radius up to distances of degrees from the
center of the cluster. Several of those stars are located at distances similar
to that of Centauri. We investigated the probability that those stars
may have been stripped off the cluster by studying their properties (mean
periods), calculating the expected halo/thick disk population of RR Lyrae stars
in this part of the sky, analyzing the radial velocity of a sub-sample of the
RR Lyrae stars, and finally, studying the probable orbits of this sub-sample
around the Galaxy. None of these investigations support the scenario that there
is significant tidal debris around Centauri, confirming previous
studies in the region. It is puzzling that tidal debris have been found
elsewhere but not near the cluster itself.Comment: 11 pages, 11 figures, Accepte
Close encounters involving RAVE stars beyond the 47 Tucanae tidal radius
The most accurate 6D phase-space information from the Radial Velocity
Experiment (RAVE) was used to integrate the orbits of 105 stars around the
galactic globular cluster 47 Tucanae, to look for close encounters between them
in the past, with a minimum distance approach less than the cluster tidal
radius. The stars are currently over the distance range 3.0 kpc d 5.5
kpc. Using the uncertainties in the current position and velocity vector for
both, star and cluster, 105 pairs of star-cluster orbits were generated in a
Monte Carlo numerical scheme, integrated over 2 Gyr and considering an
axisymmetric and non-axisymmetric Milky-Way-like Galactic potential,
respectively. In this scheme, we identified 20 potential cluster members that
had close encounters with the globular cluster 47 Tucanae, all of which have a
relative velocity distribution (V) less than 200 km s at the
minimum distance approach. Among these potential members, 9 had close
encounters with the cluster with velocities less than the escape velocity of 47
Tucanae, therefore a scenario of tidal stripping seems likely. These stars have
been classified with a 93\% confidence level, leading to the identification of
extratidal cluster stars. For the other 11 stars, V exceeds the escape
velocity of the cluster, therefore they were likely ejected or are unassociated
interlopers.Comment: 10 pages, 6 figures, 2 table, Accepted for publication in MNRA
The surface-state of the topological insulator BiSe revealed by cyclotron resonance
To date transport measurements of topological insulators have been dominated
by the conductivity of the bulk, leading to substantial difficulties in
resolving the properties of the surface. To this end, we use high magnetic
field, rf- and microwave-spectroscopy to selectively couple to the surface
conductivity of BiSe at high frequency. In the frequency range of a few
GHz we observe a crossover from quantum oscillations indicative of a small 3D
Fermi surface, to cyclotron resonance indicative of a 2D surface state
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