10,954 research outputs found
The Structural and Kinematic Evolution of Central Star Clusters in Dwarf Galaxies and Their Dependence on Dark Matter Halo Profiles
Through a suite of direct N-body simulations, we explore how the structural
and kinematic evolution of a star cluster located at the center of a dwarf
galaxy is affected by the shape of its host's dark matter density profile. The
stronger central tidal fields of cuspier halos minimize the cluster's ability
to expand in response to mass loss due to stellar evolution during its early
evolutionary stages and during its subsequent long-term evolution driven by
two-body relaxation. Hence clusters evolving in cuspier dark matter halos are
characterized by more compact sizes, higher velocity dispersions and remain
approximately isotropic at all clustercentric distances. Conversely, clusters
in cored halos can expand more and develop a velocity distribution profile that
becomes increasingly radially anisotropic at larger clustercentric distances.
Finally, the larger velocity dispersion of clusters evolving in cuspier dark
matter profiles results in them having longer relaxation times. Hence clusters
in cuspy galaxies relax at a slower rate and, consequently, they are both less
mass segregated and farther from complete energy equipartition than cluster's
in cored galaxies. Application of this work to observations allows for star
clusters to be used as tools to measure the distribution of dark matter in
dwarf galaxies and to distinguish isolated star clusters from ultra-faint dwarf
galaxies.Comment: 8 pages, 7 figures, Accepted for publication in MNRA
New insights from inside-out Doppler tomography
We present preliminary results from our investigation into using an
'inside-out' velocity space for creating a Doppler tomogram. The aim is to
transpose the inverted appearance of the Cartesian velocity space used in
normal Doppler tomography. In a comparison between normal and inside-out
Doppler tomograms of cataclysmic variables, we show that the inside-out
velocity space has the potential to produce new insights into the accretion
dynamics in these systems.Comment: 4 pages, 4 figures, conference: The Golden Age of Cataclysmic
Variables and Related Objects II, Palermo 201
What next for the CMSSM and the NUHM: Improved prospects for superpartner and dark matter detection
We present an updated analysis of the CMSSM and the NUHM using the latest
experimental data and numerical tools. We map out favored regions of Bayesian
posterior probability in light of data from the LHC, flavor observables, the
relic density and dark matter searches. We present some updated features with
respect to our previous analyses: we include the effects of corrections to the
light Higgs mass beyond the 2-loop order using FeynHiggs v2.10.0; we include in
the likelihood the latest limits from direct searches for squarks and gluinos
at ATLAS with ~20/fb; the latest constraints on the spin-independent scattering
cross section of the neutralino from LUX are applied taking into account
uncertainties in the nuclear form factors. We find that in the CMSSM the
posterior distribution now tends to favor smaller values of Msusy than in the
previous analyses. As a consequence, the statistical weight of the A-resonance
region increases to about 30% of the total probability, with interesting new
prospects for the 14 TeV run at the LHC. The most favored region, on the other
hand, still features multi-TeV squarks and gluinos, and ~1TeV higgsino dark
matter whose detection prospects by current and one-tonne detectors look very
promising. The same region is predominant in the NUHM, although the A-resonance
region is also present there as well as a new solution, of neutralino-stau
coannihilation through the channel stau stau -> hh at very large \mu. We derive
the expected sensitivity of the future CTA experiment to ~1 TeV higgsino dark
matter for both models and show that the prospects for probing both models are
realistically good. We comment on the complementarity of this search to planned
direct detection one-tonne experiments.Comment: 37 pages, 15 figures. Appendix added showing the future constraints
on the CMSSM, including an updated calculation of the sensitivity of CTA
presented in arXiv:1411.521
On the measurement of frequency and of its sample variance with high-resolution counters
A frequency counter measures the input frequency averaged over a
suitable time , versus the reference clock. High resolution is achieved
by interpolating the clock signal. Further increased resolution is obtained by
averaging multiple frequency measurements highly overlapped. In the presence of
additive white noise or white phase noise, the square uncertainty improves from
to .
Surprisingly, when a file of contiguous data is fed into the formula of the
two-sample (Allan) variance
of
the fractional frequency fluctuation , the result is the \emph{modified}
Allan variance mod . But if a sufficient number of contiguous
measures are averaged in order to get a longer and the data are fed into
the same formula, the results is the (non-modified) Allan variance. Of course
interpretation mistakes are around the corner if the counter internal process
is not well understood.Comment: 14 pages, 5 figures, 1 table, 18 reference
Did GW170817 harbor a pulsar?
If the progenitor of GW170817 harbored a pulsar, then a Poynting flux
dominated bow-shock cavity would have been expected to form around the
traveling binary. The characteristic size of this evacuated region depends
strongly on the spin-down evolution of the pulsar companion, which in turn
depends on the merging timescale of the system. If this evacuated region is
able to grow to a sufficiently large scale, then the deceleration of the jet,
and thus the onset of the afterglow, would be noticeably delayed. The first
detection of afterglow emission, which was uncovered 9.2 days after the
-ray burst trigger, can thus be used to constrain the size of a
pre-existing pulsar-wind cavity. We use this information, together with a model
of the jet to place limits on the presence of a pulsar in GW170817 and discuss
the derived constraints in the context of the observed double neutron star
binary population. We find that the majority of Galactic systems that are close
enough to merge within a Hubble time would have carved a discernibly large
pulsar-wind cavity, inconsistent with the onset timescale of the X-ray
afterglow of GW170817. Conversely, the recently detected system J1913+1102,
which host a low-luminosity pulsar, provides a congruous Milky Way analog of
GW170817's progenitor model. This study highlights the potential of the
proposed observational test for gaining insight into the origin of double
neutron star binaries, in particular if the properties of Galactic systems are
representative of the overall merging population.Comment: Accepted for publication in ApJL, 6 pages, 5 figure
A Striped Holographic Superconductor
We study inhomogeneous solutions of a 3+1-dimensional Einstein-Maxwell-scalar
theory. Our results provide a holographic model of superconductivity in the
presence of a charge density wave sourced by a modulated chemical potential. We
find that below a critical temperature superconducting stripes develop. We show
that they are thermodynamically favored over the normal state by computing the
grand canonical potential. We investigate the dependence of the critical
temperature on the modulation's wave vector, which characterizes the
inhomogeneity. We find that it is qualitatively similar to that expected for a
weakly coupled BCS theory, but we point out a quantitative difference. Finally,
we use our solutions to compute the conductivity along the direction of the
stripes.Comment: 30 pages, 11 figures, v2: references added, figure 4 replace
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