114 research outputs found
Gravity duals of half-BPS Wilson loops
We explicitly construct the fully back-reacted half-BPS solutions in Type IIB
supergravity which are dual to Wilson loops with 16 supersymmetries in
super Yang-Mills. In a first part, we use the methods of a
companion paper to derive the exact general solution of the half-BPS equations
on the space , with isometry group
in terms of two locally harmonic functions
on a Riemann surface with boundary. These solutions, generally, have
varying dilaton and axion, and non-vanishing 3-form fluxes. In a second part,
we impose regularity and topology conditions. These non-singular solutions may
be parametrized by a genus hyperelliptic surface , all of
whose branch points lie on the real line. Each genus solution has only a
single asymptotic region, but exhibits homology
3-spheres, and an extra homology 5-spheres, carrying respectively RR 3-form
and RR 5-form charges. For genus 0, we recover with 3 free
parameters, while for genus , the solution has free
parameters. The genus 1 case is studied in detail. Numerical analysis is used
to show that the solutions are regular throughout the parameter space.
Collapse of a branch cut on subtending either a homology 3-sphere or a
homology 5-sphere is non-singular and yields the genus solution. This
behavior is precisely expected of a proper dual to a Wilson loop in gauge
theory.Comment: 62 pages, LaTeX, 6 figures, v2: minor change
Brane Bremsstrahlung in DBI Inflation
We consider the effect of trapped branes on the evolution of a test brane
whose motion generates DBI inflation along a warped throat. The coupling
between the inflationary brane and a trapped brane leads to the radiation of
non-thermal particles on the trapped brane. We calculate the Gaussian spectrum
of the radiated particles and their backreaction on the DBI motion of the
inflationary brane. Radiation occurs for momenta lower than the speed of the
test brane when crossing the trapped brane. The slowing down effect is either
due to a parametric resonance when the interaction time is small compared to
the Hubble time or a tachyonic resonance when the interaction time is large. In
both cases the motion of the inflationary brane after the interaction is
governed by a chameleonic potential,which tends to slow it down. We find that a
single trapped brane can hardly slow down a DBI inflaton whose fluctuations
lead to the Cosmic Microwave Background spectrum. A more drastic effect is
obtained when the DBI brane encounters a tightly spaced stack of trapped
branes.Comment: 20 pages, 1 figur
Detecting metal-rich intermediate-age globular clusters in NGC4570 using K-band photometry
“The original publication is available at www.springerlink.com”. Copyright Springer. DOI: 10.1007/s10509-009-0093-8Globular cluster systems (GCSs) of most early-type galaxies feature two peaks in their optical colour distributions. Blue-peak globular clusters (GCs) are believed to be old and metal-poor, whereas the ages, metallicities, and the origin of the red-peak GCs are still being debated. We obtained deep K-band photometry and combined it with Hubble Space Telescope observations in g and z to yield a full spectral energy distribution from the optical to the near-infrared. This now allows us to break the age–metallicity degeneracy. We used our evolutionary synthesis models galev for star clusters to compute a large grid of models with different metallicities and a wide range of ages. Comparing these models to our observations revealed a large population of intermediate-age (1–3 Gyr) and metal-rich (≈solar-metallicity) GCs, that will give us further insights into the formation history of this galaxy.Peer reviewe
Initial mass function variability from the integrated light of diverse stellar systems
Galaxie
An Inflationary Model in String Theory
We construct a model of inflation in string theory after carefully taking
into account moduli stabilization. The setting is a warped compactification of
Type IIB string theory in the presence of D3 and anti-D3-branes. The inflaton
is the position of a D3-brane in the internal space. By suitably adjusting
fluxes and the location of symmetrically placed anti-D3-branes, we show that at
a point of enhanced symmetry, the inflaton potential V can have a broad
maximum, satisfying the condition V''/V << 1 in Planck units. On starting close
to the top of this potential the slow-roll conditions can be met. Observational
constraints impose significant restrictions. As a first pass we show that these
can be satisfied and determine the important scales in the compactification to
within an order of magnitude. One robust feature is that the scale of inflation
is low, H = O(10^{10}) GeV. Removing the observational constraints makes it
much easier to construct a slow-roll inflationary model. Generalizations and
consequences including the possibility of eternal inflation are also discussed.
A more careful study, including explicit constructions of the model in string
theory, is left for the future.Comment: 27 pages, LaTeX, 1 eps figure. v2: references adde
A SLUGGS and Gemini/GMOS combined study of the elliptical galaxy M60: wide-field photometry and kinematics of the globular cluster system
We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster. Imaging of NGC 4649 was assembled from a recently obtained Hubble Space Telescope/Advanced Camera for Surveys mosaic, and new Subaru/Suprime-Cam and archival Canada–France–Hawaii Telescope/MegaCam data. About 1200 sources were followed up spectroscopically using combined observations from three multi-object spectrographs: Keck/Deep Imaging Multi-Object Spectrograph, Gemini/Gemini Multi-Object Spectrograph and Multiple Mirror Telescope/Hectospec. We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than previous data sets and with a factor of 3 improvement in velocity precision. We confirm significant GC colour bimodality and find that the red GCs are more centrally concentrated, while the blue GCs are more spatially extended. We infer negative GC colour gradients in the innermost 20 kpc and flat gradients out to large radii. Rotation is detected along the galaxy major axis for all tracers: blue GCs, red GCs, galaxy stars and planetary nebulae. We compare the observed properties of NGC 4649 with galaxy formation models. We find that formation via a major merger between two gas-poor galaxies, followed by satellite accretion, can consistently reproduce the observations of NGC 4649 at different radii. We find no strong evidence to support an interaction between NGC 4649 and the neighbouring spiral galaxy NGC 4647. We identify interesting GC kinematic features in our data, such as counter-rotating subgroups and bumpy kinematic profiles, which encode more clues about the formation history of NGC 4649
The PL calibration for Milky Way Cepheids and its implications for the distance scale
The rationale behind recent calibrations of the Cepheid PL relation using the
Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent
conclusions regarding a possible change in slope of the PL relation for
short-period and long-period Cepheids are tied to a pathological distribution
of HST calibrators within the instability strip. A recalibration of the
period-luminosity relation is obtained using Galactic Cepheids in open clusters
and groups, the resulting relationship, described by log L/L_sun =
2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter
expected from color spread within the instability strip. The relationship is
confirmed by Cepheids with HST parallaxes, although without the need for
Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos
parallaxes, albeit with concerns about the cited precisions of the latter. A
Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for
Galactic Cepheids is tested successfully using Cepheids in the inner regions of
the galaxy NGC 4258, confirming the independent geometrical distance
established for the galaxy from OH masers. Differences between the extinction
properties of interstellar and extragalactic dust may yet play an important
role in the further calibration of the Cepheid PL relation and its application
to the extragalactic distance scale.Comment: Accepted for Publication (Astrophysics & Space Science
The SLUGGS survey: chromodynamical modelling of the lenticular galaxy NGC 1023
Globular clusters (GCs) can be considered discrete, long-lived, dynamical tracers that retain crucial information about the assembly history of their parent galaxy. In this paper, we present a new catalogue of GC velocities and colours for the lenticular galaxy NGC 1023, we study their kinematics and spatial distribution, in comparison with the underlying stellar kinematics and surface brightness profile, and we test a new method for studying GC properties. Specifically, we decompose the galaxy light into its spheroid (assumed to represent the bulge+halo components) and disc components and use it to assign to each GC a probability of belonging to one of the two components. Then we model the galaxy kinematics, assuming a disc and spheroidal component, using planetary nebulae and integrated stellar light. We use this kinematic model and the probability previously obtained from the photometry to recalculate for each GC its likelihood of being associated with the disc, the spheroid, or neither. We find that the reddest GCs are likely to be associated with the disc, as found for faint fuzzies in this same galaxy, suggesting that the disc of this S0 galaxy originated at z ≃ 2. The majority of blue GCs are found likely to be associated with the spheroidal (hot) component. The method also allows us to identify objects that are unlikely to be in equilibrium with the system. In NGC 1023 some of the rejected GCs form a substructure in phase space that is connected with NGC 1023 companion galaxy
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