1,185 research outputs found
3-Form Flux Compactification of Salam-Sezgin Supergravity
The compactification of 6 dimensional Salam-Sezgin model in the presence of
3-form flux H is investigated. We find a torus topology for this
compactification with two cusps which are the places of branes, while at the
limit of large size L of the compact direction we also obtain sphere topology.
This resembles the Randall-Sundrum I,II model. The branes at one of the cusps
can be chosen to be 3- and 4-branes which fill our 4-dimensional space together
with the fact that H=0 at this position restores the Lorentz symmetry. This
compactification also provides an example for the so-called `time warp'
solution, [0812.5107 [hep-th]]. According to a no-go theorem in , the
time warp compactification violates the null energy condition. While the
theorem is quiet for d=6, our model gives a time warp compactification which
satisfies the null energy condition. We also derive the four dimensional
effective Planck mass which is not obvious due to the time warp nature of the
solution.Comment: 19 pages, 5 fig
Supersymmetric codimension-two branes in six-dimensional gauged supergravity
We consider the six-dimensional Salam-Sezgin supergravity in the presence of
codimension-2 branes. In the case that the branes carry only tension, we
provide a way to supersymmetrise them by adding appropriate localised
Fayet-Iliopoulos terms and localised corrections to the Chern-Simons term and
modifying accordingly the fermionic supersymmetry transformations. The
resulting brane action has N=1 supersymmetry (SUSY). We find the axisymmetric
vacua of the system and show that one has unwarped background solutions with
"football"-shaped extra dimensions which always respect N=1 SUSY for any value
of the equal brane tensions, in contrast with the non-supersymmetric brane
action background. Finally, we generically find multiple zero modes of the
gravitino in this background and discuss how one could obtain a single chiral
zero mode present in the low energy spectrum.Comment: 21 pages, no figures, A sign error in the gauge potential at the
lower brane corrected and its consequent effect discusse
Sculpting the Extra Dimensions: Inflation from Codimension-2 Brane Back-reaction
We construct an inflationary model in 6D supergravity that is based on
explicit time-dependent solutions to the full higher-dimensional field
equations, back-reacting to the presence of a 4D inflaton rolling on a
space-filling codimension-2 source brane. Fluxes in the bulk stabilize all
moduli except the `breathing' modulus (that is generically present in
higher-dimensional supergravities). Back-reaction to the inflaton roll causes
the 4D Einstein-frame on-brane geometry to expand, a(t) ~ t^p, as well as
exciting the breathing mode and causing the two off-brane dimensions to expand,
r(t) ~ t^q. The model evades the general no-go theorems precluding 4D de Sitter
solutions, since adjustments to the brane-localized inflaton potential allow
the power p to be dialed to be arbitrarily large, with the 4D geometry becoming
de Sitter in the limit p -> infinity (in which case q = 0). Slow-roll solutions
give accelerated expansion with p large but finite, and q = 1/2. Because the
extra dimensions expand during inflation, the present-day 6D gravity scale can
be much smaller than it was when primordial fluctuations were generated -
potentially allowing TeV gravity now to be consistent with the much higher
gravity scale required at horizon-exit for observable primordial gravity waves.
Because p >> q, the 4 on-brane dimensions expand more quickly than the 2
off-brane ones, providing a framework for understanding why the observed four
dimensions are presently so much larger than the internal two. If uplifted to a
10D framework with 4 dimensions stabilized, the 6D evolution described here
could describe how two of the six extra dimensions evolve to become much larger
than the others, as a consequence of the enormous expansion of the 4 large
dimensions we can see.Comment: 27 pages + appendices, 2 figure
Transcriptional silencing of the Dickkopfs-3 (Dkk-3) gene by CpG hypermethylation in acute lymphoblastic leukaemia
Dkk-3 is a newly characterised mortalisation-related gene and an antagonist of the Wnt oncogenic signalling pathway whose
expression is decreased in a variety of cancer cell lines, suggesting that the Dkk-3 gene, located at chromosome 11p15.1, functions as
a tumour suppressor gene. Although 11p15 is a âhot spotâ for methylation in acute lymphoblastic leukaemia (ALL), the role of Dkk-3
abnormalities has never been evaluated in this disease. We analysed CpG island methylation of the Dkk-3 promoter in six ALL cell
lines and 183 ALL patients. We observed Dkk-3 hypermethylation in all cell lines and in cells from 33% (60/183) of ALL patients.
Moreover, Dkk-3 methylation was associated with decreased Dkk-3 mRNA expression and this expression was restored after
exposure to the demethylating agent 5-AzaC. Clinical features did not differ between hypermethylated and unmethylated patients.
Estimated disease-free survival (DFS) and overall survival at 10 and 11 years, respectively, were 49.8 and 45.6% for normal patients
and 10.5 and 15.1% for hypermethylated patients (PŒ0.001 and 0.09). Multivariate analysis demonstrated that Dkk-3 methylation
was an independent prognostic factor predicting DFS (PŒ0.0009). Our data suggest that Dkk-3 methylation occurs at an early stage
in ALL pathogenesis and probably influences the clinical behaviour of the disease
The large-scale structure of the halo of the Andromeda galaxy. I. Global stellar density, morphology and metallicity properties
We present an analysis of the large-scale structure of the halo of the Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS), currently the most complete map of resolved stellar populations in any galactic halo. Despite the presence
Scalar brane backgrounds in higher order curvature gravity
We investigate maximally symmetric brane world solutions with a scalar field.
Five-dimensional bulk gravity is described by a general lagrangian which yields
field equations containing no higher than second order derivatives. This
includes the Gauss-Bonnet combination for the graviton. Stability and
gravitational properties of such solutions are considered, and we particularily
emphasise the modifications induced by the higher order terms. In particular it
is shown that higher curvature corrections to Einstein theory can give rise to
instabilities in brane world solutions. A method for analytically obtaining the
general solution for such actions is outlined. Genericaly, the requirement of a
finite volume element together with the absence of a naked singularity in the
bulk imposes fine-tuning of the brane tension. A model with a moduli scalar
field is analysed in detail and we address questions of instability and
non-singular self-tuning solutions. In particular, we discuss a case with a
normalisable zero mode but infinite volume element.Comment: published versio
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
PAMELA/ATIC anomaly from the meta-stable extra dark matter component and the leptophilic Yukawa interaction
We present a supersymmetric model with two dark matter (DM) components
explaining the galactic positron excess observed by PAMELA/HEAT and
ATIC/PPB-BETS: One is the conventional (bino-like) lightest supersymmetric
particle (LSP) \chi, and the other is a TeV scale meta-stable neutral singlet
N_D, which is a Dirac fermion (N,N^c). In this model, N_D decays dominantly
into \chi e^+e^- through an R parity preserving dimension 6 operator with the
life time \tau_N\sim 10^{26} sec. We introduce a pair of vector-like superheavy
SU(2) lepton doublets (L,L^c) and lepton singlets (E,E^c). The dimension 6
operator leading to the N_D decay is generated from the leptophilic Yukawa
interactions by W\supset Ne^cE+Lh_dE^c+m_{3/2}l_1L^c with the dimensionless
couplings of order unity, and the gauge interaction by {\cal L}\supset \sqrt{2}
g'\tilde{e}^{c*}e^c\chi + h.c. The superheavy masses of the vector-like leptons
(M_L, M_E\sim 10^{16} GeV) are responsible for the longevity of N_D. The low
energy field spectrum in this model is just the MSSM fields and N_D. Even for
the case that the portion of N_D is much smaller than that of \chi in the total
DM density [{\cal O}(10^{-10}) \lesssim n_{N_D}/n_\chi], the observed positron
excess can be explained by adopting relatively lighter masses of the
vector-like leptons (10^{13} GeV \lesssim M_{L,E} \lesssim 10^{16} GeV). The
smallness of the electron mass is also explained. This model is easily embedded
in the flipped SU(5) grand unification, which is a leptophilic unified theory.Comment: 12 pages, published versio
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
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