200 research outputs found
Axion Inflation and Gravity Waves in String Theory
The majority of models of inflation in string theory predict an absence of
measurable gravitational waves, r << 10^{-3}. The most promising proposals for
making string theoretic models that yield measurable tensor fluctuations
involve axion fields with slightly broken shift symmetry. We consider such
models in detail, with a particular focus on the N-flation scenario and on
axion valley/natural inflation models. We find that in Calabi-Yau threefold
compactifications with logarithmic Kahler potentials K it appears to be
difficult to meet the conditions required for axion inflation in the
supergravity regime. However, in supergravities with an (approximately)
quadratic shift-symmetric K, axion inflation may be viable. Such Kahler
potentials do arise in some string models, in specific limits of the moduli
space. We describe the most promising classes of models; more detailed study
will be required before one can conclude that working models exist.Comment: 30 + 16 pages, 5 figures. Added references, corrected typo
A genetic algorithm to minimize chromatic entropy
We present an algorithmic approach to solving the problem of chromatic entropy, a combinatorial optimization problem related to graph coloring. This problem is a component in algorithms for optimizing data compression when computing a function of two correlated sources at a receiver. Our genetic algorithm for minimizing chromatic entropy uses an order-based genome inspired by graph coloring genetic algorithms, as well as some problem-specific heuristics. It performs consistently well on synthetic instances, and for an expositional set of functional compression problems, the GA routinely finds a compression scheme that is 20-30% more efficient than that given by a reference compression algorithm
Volume Weighted Measures of Eternal Inflation in the Bousso-Polchinski Landscape
We consider the cosmological dynamics associated with volume weighted
measures of eternal inflation, in the Bousso-Polchinski model of the string
theory landscape. We find that this measure predicts that observers are most
likely to find themselves in low energy vacua with one flux considerably larger
than the rest. Furthermore, it allows for a satisfactory anthropic explanation
of the cosmological constant problem by producing a smooth, and approximately
constant, distribution of potentially observable values of Lambda. The low
energy vacua selected by this measure are often short lived. If we require
anthropically acceptable vacua to have a minimum life-time of 10 billion years,
then for reasonable parameters a typical observer should expect their vacuum to
have a life-time of approximately 12 billion years. This prediction is model
dependent, but may point toward a solution to the coincidence problem of
cosmology.Comment: 35 pages, 8 figure
The Type II Supernova Rate in z~0.1 Galaxy Clusters from the Multi-Epoch Nearby Cluster Survey
We present 7 spectroscopically confirmed Type II cluster supernovae (SNeII)
discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey
targeting 57 low redshift 0.05 < z < 0.15 galaxy clusters with the
Canada-France-Hawaii Telescope. We find the rate of Type II supernovae within
the virial radius of these galaxy clusters to be 0.026 (+0.085 -0.018 stat;
+0.003 -0.001 sys) SNe per century per 1e10 solar masses. Surprisingly, one
SNII is in a red sequence host galaxy that shows no clear evidence of recent
star formation. This is unambiguous evidence in support of ongoing, low-level
star formation in at least some cluster elliptical galaxies, and illustrates
that galaxies that appear to be quiescent cannot be assumed to host only Type
Ia SNe. Based on this single SNII we make the first measurement of the SNII
rate in red sequence galaxies, and find it to be 0.007 (+0.014 -0.007 stat;
+0.009 -0.001 sys) SNe per century per 1e10 solar masses. We also make the
first derivation of cluster specific star formation rates (sSFR) from cluster
SNII rates. We find that for all galaxy types, sSFR is 5.1 (+15.8 -3.1 stat;
+0.9 -0.9 sys) solar masses per year per 1e12 solar masses, and for red
sequence galaxies only, it is 2.0 (+4.2 -0.9 stat; +0.4 -0.4 sys) solar masses
per year per 1e12 solar masses. These values agree with SFRs measured from
infrared and ultraviolet photometry, and H-alpha emission from optical
spectroscopy. Additionally, we use the SFR derived from our SNII rate to show
that although a small fraction of cluster Type Ia SNe may originate in the
young stellar population and experience a short delay time, these results do
not preclude the use of cluster SNIa rates to derive the late-time delay time
distribution for SNeIa.Comment: 16 pages, 5 tables, 6 figures, 2 appendices; accepted to Ap
HST viewing of spectacular star-forming trails behind ESO 137-001
We present the results from the HST WFC3 and ACS data on an archetypal galaxy
undergoing ram pressure stripping (RPS), ESO 137-001, in the nearby cluster
Abell 3627. ESO 137-001 is known to host a prominent stripped tail detected in
many bands from X-rays, Halpha to CO. The HST data reveal significant features
indicative of RPS such as asymmetric dust distribution and surface brightness
as well as many blue young star complexes in the tail. We study the correlation
between the blue young star complexes from HST, HII regions from Halpha (MUSE)
and dense molecular clouds from CO (ALMA). The correlation between the HST blue
star clusters and the HII regions is very good, while their correlation with
the dense CO clumps are typically not good, presumably due in part to
evolutionary effects. In comparison to the Starburst99+Cloudy model, many blue
regions are found to be young (< 10 Myr) and the total star formation (SF) rate
in the tail is 0.3 - 0.6 M_Sun/yr for sources measured with ages less than 100
Myr, about 40% of the SF rate in the galaxy. We trace SF over at least 100 Myr
and give a full picture of the recent SF history in the tail. We also
demonstrate the importance of including nebular emissions and a nebular to
stellar extinction correction factor when comparing the model to the broadband
data. Our work on ESO 137-001 demonstrates the importance of HST data for
constraining the SF history in stripped tails.Comment: 21 pages, 19 figures, 4 tables, re-submitted to MNRAS (initial
submission on Aug. 4, 2022
The Inflationary Wavefunction and its Initial Conditions
We explore the effect of initial conditions on the inflationary wavefunction
and their consequences for the observed spectrum of primordial fluctuations. In
a class of models with a sudden transition into inflation we find that, for a
reasonable set of assumptions about the reheat temperature and the number of
e-foldings, it is possible for initial conditions set by a pre-inflationary
epoch to have an observable effect.Comment: 17 pages, 1 figure, numerical example and analysis thereof added in
this versio
Metal enrichment of the intra-cluster medium by thermally and cosmic-ray driven galactic winds
We investigate the efficiency and time-dependence of thermally and cosmic ray
driven galactic winds for the metal enrichment of the intra-cluster medium
(ICM) using a new analytical approximation for the mass outflow. The spatial
distribution of the metals are studied using radial metallicity profiles and 2D
metallicity maps of the model clusters as they would be observed by X-ray
telescopes like XMM-Newton. Analytical approximations for the mass loss by
galactic winds driven by thermal and cosmic ray pressure are derived from the
Bernoulli equation and implemented in combined N-body/hydrodynamic cosmological
simulations with a semi-analytical galaxy formation model. Observable
quantities like the mean metallicity, metallicity profiles, and 2D metal maps
of the model clusters are derived from the simulations. We find that galactic
winds alone cannot account for the observed metallicity of the ICM. At redshift
the model clusters have metallicities originating from galactic winds
which are almost a factor of 10 lower than the observed values. For massive,
relaxed clusters we find, as in previous studies, a central drop in the
metallicity due to a suppression of the galactic winds by the pressure of the
ambient ICM. Combining ram-pressure stripping and galactic winds we find radial
metallicity profiles of the model clusters which agree qualitatively with
observed profiles. Only in the inner parts of massive clusters the observed
profiles are steeper than in the simulations. Also the combination of galactic
winds and ram-pressure stripping yields too low values for the ICM
metallicities. The slope of the redshift evolution of the mean metallicity in
the simulations agrees reasonably well with recent observations.Comment: 9 pages, 6 figures, accepted by A&
Accidental Inflation in String Theory
We show that inflation in type IIB string theory driven by the volume modulus
can be realized in the context of the racetrack-based Kallosh-Linde model (KL)
of moduli stabilization. Inflation here arises through the volume modulus
slow-rolling down from a flat hill-top or inflection point of the scalar
potential. This situation can be quite generic in the landscape, where by
uplifting one of the two adjacent minima one can turn the barrier either to a
flat saddle point or to an inflection point supporting eternal inflation. The
resulting spectral index is tunable in the range of 0.93 < n_s < 1, and there
is only negligible production of primordial gravitational waves r < 10^{-6}.
The flatness of the potential in this scenario requires fine-tuning, which may
be justified taking into account the exponential reward by volume factors
preferring the regions of the universe with the maximal amount of slow-roll
inflation. This consideration leads to a tentative prediction of the spectral
index or depending on whether the
potential has a symmetry phi -> - phi or not.Comment: 15 pages, 6 figures, LaTeX, uses RevTex
Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons
The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions
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