267 research outputs found
Supergravity Higgs Inflation and Shift Symmetry in Electroweak Theory
We present a model of inflation in a supergravity framework in the Einstein
frame where the Higgs field of the next to minimal supersymmetric standard
model (NMSSM) plays the role of the inflaton. Previous attempts which assumed
non-minimal coupling to gravity failed due to a tachyonic instability of the
singlet field during inflation. A canonical K\"{a}hler potential with
\textit{minimal coupling} to gravity can resolve the tachyonic instability but
runs into the -problem. We suggest a model which is free of the
-problem due to an additional coupling in the K\"{a}hler potential which
is allowed by the Standard Model gauge group. This induces directions in the
potential which we call K-flat. For a certain value of the new coupling in the
(N)MSSM, the K\"{a}hler potential is special, because it can be associated with
a certain shift symmetry for the Higgs doublets, a generalization of the shift
symmetry for singlets in earlier models. We find that K-flat direction has
This shift symmetry is broken by interactions coming from
the superpotential and gauge fields. This direction fails to produce successful
inflation in the MSSM but produces a viable model in the NMSSM. The model is
specifically interesting in the Peccei-Quinn (PQ) limit of the NMSSM. In this
limit the model can be confirmed or ruled-out not just by cosmic microwave
background observations but also by axion searches.Comment: matches the published version at JCA
Do stochastic inhomogeneities affect dark-energy precision measurements?
The effect of a stochastic background of cosmological perturbations on the
luminosity-redshift relation is computed to second order through a recently
proposed covariant and gauge-invariant light-cone averaging procedure. The
resulting expressions are free from both ultraviolet and infrared divergences,
implying that such perturbations cannot mimic a sizable fraction of dark
energy. Different averages are estimated and depend on the particular function
of the luminosity distance being averaged. The energy flux, being minimally
affected by perturbations at large z, is proposed as the best choice for
precision estimates of dark-energy parameters. Nonetheless, its irreducible
(stochastic) variance induces statistical errors on \Omega_{\Lambda}(z)
typically lying in the few-percent range.Comment: 5 pages, 3 figures. Comments and references added. Typos corrected.
Version accepted for publication in Phys. Rev. Let
âGreen Pocketsâ as Microclimate Modifiers in UK Urban Schools
The rapid densification of many UK cities poses significant pressure on the design of schools within inner city centres. Londonâs air quality has been associated to increased mortality, and pollution and noise levels have exceeded acceptable standards. As a consequence, most schools are mechanically ventilated and have little or no contact with the outdoors, with detrimental effects for the physical and mental development of students (Charles, 2015). This study investigates the possibility of improving the design of usually neglected and underexploited outdoor and semi-outdoor spaces within urban learning environments in order to convert these spaces into microclimatic modifiers and natural air filters. The research focused on the integration of green spaces into three different environments: outdoor courtyard, semi-outdoor break-out space and indoor classroom. The findings of the analysis and design implementations indicate that the positive microclimatic effect of the green courtyard can be successfully used to achieve thermal comfort in semi-outdoor and indoor spaces throughout the year while improving visual comfort and air quality
Cosmic Microwave Background Observables of Small Field Models of Inflation
We construct a class of single small field models of inflation that can
predict, contrary to popular wisdom, an observable gravitational wave signal in
the cosmic microwave background anisotropies. The spectral index, its running,
the tensor to scalar ratio and the number of e-folds can cover all the
parameter space currently allowed by cosmological observations. A unique
feature of models in this class is their ability to predict a negative spectral
index running in accordance with recent cosmic microwave background
observations. We discuss the new class of models from an effective field theory
perspective and show that if the dimensionless trilinear coupling is small, as
required for consistency, then the observed spectral index running implies a
high scale of inflation and hence an observable gravitational wave signal. All
the models share a distinct prediction of higher power at smaller scales,
making them easy targets for detection.Comment: 13 pages, 3 figures, added numerical analysis and discussion on the
properties of the spectra. Version to be published in JCA
Backreaction on the luminosity-redshift relation from gauge invariant light-cone averaging
Using a recently proposed gauge invariant formulation of light-cone
averaging, together with adapted "geodesic light-cone" coordinates, we show how
an "induced backreaction" effect emerges, in general, from correlated
fluctuations in the luminosity distance and covariant integration measure.
Considering a realistic stochastic spectrum of inhomogeneities of primordial
(inflationary) origin we find that both the induced backreaction on the
luminosity-redshift relation and the dispersion are larger than naively
expected. On the other hand the former, at least to leading order and in the
linear perturbative regime, cannot account by itself for the observed effects
of dark energy at large-redshifts. A full second-order calculation, or even
better a reliable estimate of contributions from the non-linear regime, appears
to be necessary before firm conclusions on the correct interpretation of the
data can be drawn.Comment: 22 pages, 4 figures. Comments and references added, Fig. 1 modified.
Version accepted for publication in JCA
Quantum Gravity Constraints on Inflation
We study quantum gravity constraints on inflationary model building. Our
approach is based on requiring the entropy associated to a given inflationary
model to be less than that of the de Sitter entropy. We give two prescriptions
for determining the inflationary entropy, based on either `bits per unit area'
or entanglement entropy. The existence of transPlanckian flat directions,
necessary for large tensor modes in the CMB, correlates with an inflationary
entropy greater than that allowed by de Sitter space. Independently these
techniques also constrain or exclude de Sitter models with large-rank gauge
groups and high UV cutoffs, such as racetrack inflation or the KKLT
construction.Comment: 22 pages; v2 references adde
Volume modulus inflection point inflation and the gravitino mass problem
Several models of inflection point inflation with the volume modulus as the
inflaton are investigated. Non-perturbative superpotentials containing two
gaugino condensation terms or one such term with threshold corrections are
considered. It is shown that the gravitino mass may be much smaller than the
Hubble scale during inflation if at least one of the non-perturbative terms has
a positive exponent. Higher order corrections to the Kahler potential have to
be taken into account in such models. Those corrections are used to stabilize
the potential in the axion direction in the vicinity of the inflection point.
Models with only negative exponents require uplifting and in consequence have
the supersymmetry breaking scale higher than the inflation scale. Fine-tuning
of parameters and initial conditions is analyzed in some detail for both types
of models. It is found that fine-tuning of parameters in models with heavy
gravitino is much stronger than in models with light gravitino. It is shown
that recently proposed time dependent potentials can provide a solution to the
problem of the initial conditions only in models with heavy gravitino. Such
potentials can not be used to relax fine tuning of parameters in any model
because this would lead to values of the spectral index well outside the
experimental bounds.Comment: 27 pages, 9 figures, comments and references added, version to be
publishe
Transplanckian axions !?
We discuss quantum gravitational effects in Einstein theory coupled to
periodic axion scalars to analyze the viability of several proposals to achieve
superplanckian axion periods (aka decay constants) and their possible
application to large field inflation models. The effects we study correspond to
the nucleation of euclidean gravitational instantons charged under the axion,
and our results are essentially compatible with (but independent of) the Weak
Gravity Conjecture, as follows: Single axion theories with superplanckian
periods contain gravitational instantons inducing sizable higher harmonics in
the axion potential, which spoil superplanckian inflaton field range. A similar
result holds for multi-axion models with lattice alignment (like the
Kim-Nilles-Peloso model). Finally, theories with axions can still achieve a
moderately superplanckian periodicity (by a factor) with no higher
harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in
this case due to the absence of some instantons, which are forbidden by a
discrete gauge symmetry. Finally we discuss the realization of
these instantons as euclidean D-branes in string compactifications.Comment: 46 pages, 6 figures. Added references, clarifications, and missing
factor of 1/2 to instanton action. Conclusions unchange
Nonpromoter methylation of the CDKN2A gene with active transcription is associated with improved locoregional control in laryngeal squamous cell carcinoma
We previously reported a novel association between CDKN2A nonpromoter methylation and transcription (ARF/INK4a) in human papillomavirus associated oropharyngeal tumors. In this study we assessed whether nonpromoter CDKN2A methylation in laryngeal squamous cell carcinomas (LXSCC) conferred a similar association with transcription that predicted patient outcome. We compared DNA methylation and ARF/INK4a RNA expression levels for the CDKN2A locus using the Illumina HumanMethylation27 beadchip and RT-PCR in 43 LXSCC tumor samples collected from a prospective study of head and neck cancer patients treated at Montefiore Medical Center (MMC). Validation was performed using RNAseq data on 111 LXSCC tumor samples from the Cancer Genome Atlas (TCGA). The clinical relevance of combined nonpromoter CDKN2A methylation and transcription was assessed by multivariate Cox regression for locoregional recurrence on a subset of 69 LXSCC patients with complete clinicopathologic data from the MMC and TCGA cohorts. We found evidence of CDKN2A nonpromoter hypermethylation in a third of LXSCC from our MMC cohort, which was significantly associated with increased ARF and INK4a RNA expression (Wilcoxon rank-sum, PÂ =Â 0.007 and 0.003, respectively). A similar association was confirmed in TCGA samples (Wilcoxon rank-sum test PÂ <Â 0.0001 for ARF and INK4a). Patients with CDKN2A hypermethylation or high ARF/INK4a expression were significantly less likely to develop a locoregional recurrence compared to those with neither of the features, independent of other clinicopatholgic risk factors (adjusted hazard ratio=0.21, 95% confidence interval:0.05-0.81). These results support the conclusion that CDKN2A nonpromoter methylation is associated with increased ARF and INK4a RNA expression, and improved locoregional control in LXSCC
Inflation with racetrack superpotential and matter field
Several models of inflation with the racetrack superpotential for the volume
modulus coupled to a matter field are investigated. In particular, it is shown
that two classes of racetrack inflation models, saddle point and inflection
point ones, can be constructed in a fully supersymmetric framework with the
matter field F-term as a source of supersymmetry breaking and uplifting. Two
models of F-term supersymmetry breaking are considered: the Polonyi model and
the quantum corrected O'Raifeartaigh model. In the former case, both classes of
racetrack inflation models differ significantly from the corresponding models
with non-supersymmetric uplifting. The main difference is a quite strong
dominance of the inflaton by the matter field. In addition, fine-tuning of the
parameters is relaxed as compared to the original racetrack models. In the case
of the racetrack inflation models coupled to the O'Raifeartaigh model, the
matter field is approximately decoupled from the inflationary dynamics. In all
of the above models the gravitino mass is larger than the Hubble scale during
inflation. The possibility of having the gravitino much lighter than the Hubble
scale is also investigated. It is very hard to construct models with light
gravitino in which the volume modulus dominates inflation. On the other hand,
models in which the inflationary dynamics is dominated by the matter field are
relatively simple and seem to be more natural.Comment: 40 pages, 13 figures, references added, typos corrected, version to
be publishe
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