198 research outputs found
Diurnal modulation signal from dissipative hidden sector dark matter
We consider a simple generic dissipative dark matter model: a hidden sector
featuring two dark matter particles charged under an unbroken
interaction. Previous work has shown that such a model has the potential to
explain dark matter phenomena on both large and small scales. In this
framework, the dark matter halo in spiral galaxies features nontrivial
dynamics, with the halo energy loss due to dissipative interactions balanced by
a heat source. Ordinary supernovae can potentially supply this heat provided
kinetic mixing interaction exists with strength . This
type of kinetically mixed dark matter can be probed in direct detection
experiments. Importantly, this self-interacting dark matter can be captured
within the Earth and shield a dark matter detector from the halo wind, giving
rise to a diurnal modulation effect. We estimate the size of this effect for
detectors located in the Southern hemisphere, and find that the modulation is
large () for a wide range of parameters.Comment: 12 pages, 4 figures, clarifying comments and references adde
Mimetic gravity: a review of recent developments and applications to cosmology and astrophysics
Mimetic gravity is a Weyl-symmetric extension of General Relativity, related
to the latter by a singular disformal transformation, wherein the appearance of
a dust-like perfect fluid can mimic cold dark matter at a cosmological level.
Within this framework, it is possible to provide an unified geometrical
explanation for dark matter, the late-time acceleration, and inflation, making
it a very attractive theory. In this review, we summarize the main aspects of
mimetic gravity, as well as extensions of the minimal formulation of the model.
We devote particular focus to the reconstruction technique, which allows the
realization of any desired expansionary history of the Universe by an accurate
choice of potential, or other functions defined within the theory (as in the
case of mimetic gravity). We briefly discuss cosmological perturbation
theory within mimetic gravity. As a case study within which we apply the
concepts previously discussed, we study a mimetic Ho\v{r}ava-like theory, of
which we explore solutions and cosmological perturbations in detail. Finally,
we conclude the review by discussing static spherically symmetric solutions
within mimetic gravity, and apply our findings to the problem of galactic
rotation curves. Our review provides an introduction to mimetic gravity, as
well as a concise but self-contained summary of recent findings, progresses,
open questions, and outlooks on future research directions.Comment: 68 pages, invited review to appear in Advances in High Energy Physic
The state of the dark energy equation of state circa 2023
We critically examine the state of current constraints on the dark energy (DE) equation of state (EoS) w. Our study is motivated by the observation that, while broadly consistent with the cosmological constant value w = -1, several independent probes appear to point towards a slightly phantom EoS (w ∼ -1.03) which, if confirmed, could have important implications for the Hubble tension. We pay attention to the apparent preference for phantom DE from Planck Cosmic Microwave Background (CMB) data alone, whose origin we study in detail and attribute to a wide range of (physical and geometrical) effects. We deem the combination of Planck CMB, Baryon Acoustic Oscillations, Type Ia Supernovae, and Cosmic Chronometers data to be particularly trustworthy, inferring from this final consensus dataset w = -1.013+0.038-0.043, in excellent agreement with the cosmological constant value. Overall, despite a few scattered hints, we find no compelling evidence forcing us away from the cosmological constant (yet)
Decrease in n-acetylaspartate following concussion may be coupled to decrease in creatine
Objectives: To assess the time course changes in brain N-acetylaspartate (NAA) and creatine (Cr) in athletes who suffered a sport-related concussion. Participants: Eleven non-consecutive concussed athletes and 11 sex and age-matched control volunteers.
Main outcome measures: At 3, 15, 30 and 45 days post-injury, athletes were examined by proton Magnetic Resonance Spectroscopy (1H-MRS) for the determination of NAA,(Cr) and choline (Cho). 1H-MRS data recorded in the control group were used for comparison. Results: Compared to controls (2.18 ± 0.19), athletes showed an NAA/Cr
increase at 3 (2.71 ± 0.16; p < 0.01) and 15 days (2.54 ± 0.21; p < 0.01), followed by a decrease and subsequent normalization at 30 (1.95 ± 0.16, p < 0.05) and 45 days(2.17 ± 0.20; p <0.05) post-concussion. NAA/Cho decreased at 3, 15 and 30 days post-injury (p < 0.01 compared to controls), with no differences from controls at 45 days post-concussion. Significant increase in the Cho/Cr after 3 (+33%, p < 0.01) and 15 (+31.5%, p < 0.01) days post-injury was observed, whilst no differences compared to controls were recorded at 30 and 45 days post-impact. Conclusions: This cohort of
athletes indicates that concussion may cause concomitant decrease in cerebral NAA and Cr. This occurrence provokes longer time of metabolism normalization, as well as
longer resolution time of concussion-associated clinical symptoms
Formation of a disk structure in the symbiotic binary AX Per during its 2007-10 precursor-type activity
AX Per is an eclipsing symbiotic binary. During active phases, deep narrow
minima are observed in its light curve, and the ionization structure in the
binary changes significantly. From 2007.5, AX Per entered a new active phase.
It was connected with a significant enhancement of the hot star wind.
Simultaneously, we identified a variable optically thick warm (Teff ~ 6000 K)
source that contributes markedly to the composite spectrum. The source was
located at the hot star's equator and has the form of a flared disk, whose
outer rim simulates the warm photosphere. The formation of the neutral
disk-like zone around the accretor during the active phase was connected with
its enhanced wind. We suggested that this connection represents a common origin
of the warm pseudophotospheres that are indicated during the active phases of
symbiotic stars.Comment: 13 pages, 9 figures, 8 tables, accepted for A&
- …