86 research outputs found
Dark matter annihilation or unresolved astrophysical sources? Anisotropy probe of the origin of cosmic gamma-ray background
The origin of the cosmic gamma-ray background (CGB) is a longstanding mystery
in high-energy astrophysics. Possible candidates include ordinary astrophysical
objects such as unresolved blazars, as well as more exotic processes such as
dark matter annihilation. While it would be difficult to distinguish them from
the mean intensity data alone, one can use anisotropy data instead. We
investigate the CGB anisotropy both from unresolved blazars and dark matter
annihilation (including contributions from dark matter substructures), and find
that the angular power spectra from these sources are very different. We then
focus on detectability of dark matter annihilation signals using the anisotropy
data, by treating the unresolved blazar component as a known background. We
find that the dark matter signature should be detectable in the angular power
spectrum of the CGB from two-year all-sky observations with the Gamma Ray Large
Area Space Telescope (GLAST), as long as the dark matter annihilation
contributes to a reasonable fraction, e.g., >~ 0.3, of the CGB at around 10
GeV. We conclude that the anisotropy measurement of the CGB with GLAST should
be a powerful tool for revealing the CGB origin, and potentially for the first
detection of dark matter annihilation.Comment: 17 pages, 8 figures; minor revision; accepted by Physical Review
A common brain network among state, trait, and pathological anxiety from whole-brain functional connectivity
Anxiety is one of the most common mental states of humans. Although it drives us to avoid frightening situations and to achieve our goals, it may also impose significant suffering and burden if it becomes extreme. Because we experience anxiety in a variety of forms, previous studies investigated neural substrates of anxiety in a variety of ways. These studies revealed that individuals with high state, trait, or pathological anxiety showed altered neural substrates. However, no studies have directly investigated whether the different dimensions of anxiety share a common neural substrate, despite its theoretical and practical importance. Here, we investigated a brain network of anxiety shared by different dimensions of anxiety in a unified analytical framework using functional magnetic resonance imaging (fMRI). We analyzed different datasets in a single scale, which was defined by an anxiety-related brain network derived from whole brain. We first conducted the anxiety provocation task with healthy participants who tended to feel anxiety related to obsessive-compulsive disorder (OCD) in their daily life. We found a common state anxiety brain network across participants (1585 trials obtained from 10 participants). Then, using the resting-state fMRI in combination with the participants' behavioral trait anxiety scale scores (879 participants from the Human Connectome Project), we demonstrated that trait anxiety shared the same brain network as state anxiety. Furthermore, the brain network between common to state and trait anxiety could detect patients with OCD, which is characterized by pathological anxiety-driven behaviors (174 participants from multi-site datasets). Our findings provide direct evidence that different dimensions of anxiety have a substantial biological inter-relationship. Our results also provide a biologically defined dimension of anxiety, which may promote further investigation of various human characteristics, including psychiatric disorders, from the perspective of anxiety
Gamma-Ray Luminosity Function of Blazars and the Cosmic Gamma-Ray Background: Evidence for the Luminosity Dependent Density Evolution
We present a comprehensive study for the gamma-ray luminosity function (GLF)
of blazars and their contribution to the extragalactic diffuse gamma-ray
background (EGRB). Radio and gamma-ray luminosity correlation is introduced to
take into account the radio detectability which is important for the blazar
identification. Previous studies considered only pure luminosity evolution
(PLE) or pure density evolution, but we introduce the luminosity dependent
density evolution (LDDE) model, which is favored from the evolution of X-ray
luminosity function (XLF) of AGNs. The model parameters are constrained by
likelihood analyses about the observed redshift and gamma-ray flux
distributions of the EGRET blazars. We find that the LDDE model gives a better
fit to the observed distributions than the PLE model, indicating that the LDDE
model is also appropriate for gamma-ray blazars, and that the jet activity is
universally correlated with the accretion history of AGNs. The normalization
between the GLF and XLF is consistent with the unified picture of AGNs, when
the beaming and a reasonable duty cycle of jet activity are taken into account.
We then find that only 25--50% of the EGRB can be explained by unresolved
blazars with the best-fit LDDE parameters. Unresolved blazars can account for
all the EGRB only with a steeper index of the faint-end slope of the GLF, which
is marginally consistent with the EGRET data but inconsistent with that of the
XLF. Therefore unresolved AGNs cannot be the dominant source of the EGRB,
unless there is a new population of gamma-ray emitting AGNs that evolves
differently from the XLF of AGNs. Predictions for the GLAST mission are made,
and we find that the best-fit LDDE model predicts about 3000 blazars in the
entire sky, which is considerably fewer than a previous estimate.Comment: 13 pages, 12 figures, accepted by ApJ; minor typos corrected and some
figures revised, main conclusions essentially unchange
Why I tense up when you watch me: inferior parietal cortex mediates an audience’s influence on motor performance
The presence of an evaluative audience can alter skilled motor performance through changes in force output. To investigate how this is mediated within the brain, we emulated real-time social monitoring of participants’ performance of a fine grip task during functional magnetic resonance neuroimaging. We observed an increase in force output during social evaluation that was accompanied by focal reductions in activity within bilateral inferior parietal cortex. Moreover, deactivation of the left inferior parietal cortex predicted both inter- and intra-individual differences in socially-induced change in grip force. Social evaluation also enhanced activation within the posterior superior temporal sulcus, which conveys visual information about others’ actions to the inferior parietal cortex. Interestingly, functional connectivity between these two regions was attenuated by social evaluation. Our data suggest that social evaluation can vary force output through the altered engagement of inferior parietal cortex; a region implicated in sensorimotor integration necessary for object manipulation, and a component of the action-observation network which integrates and facilitates performance of observed actions. Social-evaluative situations may induce high-level representational incoherence between one’s own intentioned action and the perceived intention of others which, by uncoupling the dynamics of sensorimotor facilitation, could ultimately perturbe motor output
Neural correlates of enhanced visual short-term memory for angry faces: An fMRI study
Copyright: © 2008 Jackson et al.Background: Fluid and effective social communication requires that both face identity and emotional expression information are encoded and maintained in visual short-term memory (VSTM) to enable a coherent, ongoing picture of the world and its players. This appears to be of particular evolutionary importance when confronted with potentially threatening displays of emotion - previous research has shown better VSTM for angry versus happy or neutral face identities.Methodology/Principal Findings: Using functional magnetic resonance imaging, here we investigated the neural correlates of this angry face benefit in VSTM. Participants were shown between one and four to-be-remembered angry, happy, or neutral faces, and after a short retention delay they stated whether a single probe face had been present or not in the previous display. All faces in any one display expressed the same emotion, and the task required memory for face identity. We find enhanced VSTM for angry face identities and describe the right hemisphere brain network underpinning this effect, which involves the globus pallidus, superior temporal sulcus, and frontal lobe. Increased activity in the globus pallidus was significantly correlated with the angry benefit in VSTM. Areas modulated by emotion were distinct from those modulated by memory load.Conclusions/Significance: Our results provide evidence for a key role of the basal ganglia as an interface between emotion and cognition, supported by a frontal, temporal, and occipital network.The authors were supported by a Wellcome Trust grant (grant number 077185/Z/05/Z) and by BBSRC (UK) grant BBS/B/16178
Dark Matter Annihilation around Intermediate Mass Black Holes: an update
The formation and evolution of Black Holes inevitably affects the
distribution of dark and baryonic matter in the neighborhood of the Black Hole.
These effects may be particularly relevant around Supermassive and Intermediate
Mass Black Holes (IMBHs), the formation of which can lead to large Dark Matter
overdensities, called {\em spikes} and {\em mini-spikes} respectively. Despite
being larger and more dense, spikes evolve at the very centers of galactic
halos, in regions where numerous dynamical effects tend to destroy them.
Mini-spikes may be more likely to survive, and they have been proposed as
worthwhile targets for indirect Dark Matter searches. We review here the
formation scenarios and the prospects for detection of mini-spikes, and we
present new estimates for the abundances of mini-spikes to illustrate the
sensitivity of such predictions to cosmological parameters and uncertainties
regarding the astrophysics of Black Hole formation at high redshift. We also
connect the IMBHs scenario to the recent measurements of cosmic-ray electron
and positron spectra by the PAMELA, ATIC, H.E.S.S., and Fermi collaborations.Comment: 12 pages, 7 figures. Invited contribution to NJP Focus Issue on "Dark
Matter and Particle Physics
The Signature of Large Scale Structures on the Very High Energy Gamma-Ray Sky
If the diffuse extragalactic gamma ray emission traces the large scale
structures of the universe, peculiar anisotropy patterns are expected in the
gamma ray sky. In particular, because of the cutoff distance introduced by the
absorption of 0.1-10 TeV photons on the infrared/optical background, prominent
correlations with the local structures within a range of few hundreds Mpc
should be present. We provide detailed predictions of the signal based on the
PSCz map of the local universe. We also use mock N-body catalogues complemented
with the halo model of structures to study some statistical features of the
expected signatures. The results are largely independent from cosmological
details, and depend mostly on the index of correlation (or bias) of the sources
with respect to the large scale distribution of galaxies. For instance, the
predicted signal in the case of a quadratic correlation (as it may happen for a
dark matter annihilation contribution to the diffuse gamma flux) differs
substantially from a linear correlation case, providing a complementary tool to
unveil the nature of the sources of the diffuse gamma ray emission. The chances
of the present and future space and ground based observatories to measure these
features are discussed.Comment: 26 pages, 9 figures; matches published versio
Structural covariance of neostriatal and limbic regions in patients with obsessive-compulsive disorder
Background: Frontostriatal and frontoamygdalar connectivity alterations in patients with obsessive-compulsive disorder (OCD) have been typically described in functional neuroimaging studies. However, structural covariance, or volumetric correlations across distant brain regions, also provides network-level information. Altered structural covariance has been described in patients with different psychiatric disorders, including OCD, but to our knowledge, alterations within frontostriatal and frontoamygdalar circuits have not been explored. Methods: We performed a mega-analysis pooling structural MRI scans from the Obsessive-compulsive Brain Imaging Consortium and assessed whole-brain voxel-wise structural covariance of 4 striatal regions (dorsal and ventral caudate nucleus, and dorsal-caudal and ventral-rostral putamen) and 2 amygdalar nuclei (basolateral and centromedial-superficial). Images were preprocessed with the standard pipeline of voxel-based morphometry studies using Statistical Parametric Mapping software. Results: Our analyses involved 329 patients with OCD and 316 healthy controls. Patients showed increased structural covariance between the left ventral-rostral putamen and the left inferior frontal gyrus/frontal operculum region. This finding had a significant interaction with age; the association held only in the subgroup of older participants. Patients with OCD also showed increased structural covariance between the right centromedial-superficial amygdala and the ventromedial prefrontal cortex. Limitations: This was a cross-sectional study. Because this is a multisite data set analysis, participant recruitment and image acquisition were performed in different centres. Most patients were taking medication, and treatment protocols differed across centres. Conclusion: Our results provide evidence for structural network-level alterations in patients with OCD involving 2 frontosubcortical circuits of relevance for the disorder and indicate that structural covariance contributes to fully characterizing brain alterations in patients with psychiatric disorders
Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
The first three months of sky-survey operation with the Fermi Gamma Ray Space
Telescope (Fermi) Large Area Telescope (LAT) reveals 132 bright sources at
|b|>10 deg with test statistic greater than 100 (corresponding to about 10
sigma). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicate
high-confidence associations of 106 of these sources with known AGNs. This
sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two
radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of
57 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 5 blazars with
uncertain classification. Four new blazars were discovered on the basis of the
LAT detections. Remarkably, the LBAS includes 10 high-energy peaked BL Lacs
(HBLs), sources which were so far hard to detect in the GeV range. Another 10
lower-confidence associations are found. Only thirty three of the sources, plus
two at |b|>10 deg, were previously detected with EGRET, probably due to the
variable nature of these sources. The analysis of the gamma-ray properties of
the LBAS sources reveals that the average GeV spectra of BL Lac objects are
significantly harder than the spectra of FSRQs. No significant correlation
between radio and peak gamma-ray fluxes is observed. Blazar log N - log S and
luminosity functions are constructed to investigate the evolution of the
different blazar classes, with positive evolution indicated for FSRQs but none
for BLLacs. The contribution of LAT-blazars to the total extragalactic
gamma-ray intensity is estimated.Comment: Submitted to ApJ. Not yet refereed. 61 pages, 26 figure
The Luminosity Function of Fermi-detected Flat-Spectrum Radio Quasars
Fermi has provided the largest sample of {\gamma}-ray selected blazars to
date. In this work we use a complete sample of FSRQs detected during the first
year of operation to determine the luminosity function (LF) and its evolution
with cosmic time. The number density of FSRQs grows dramatically up to redshift
\sim0.5-2.0 and declines thereafter. The redshift of the peak in the density is
luminosity dependent, with more luminous sources peaking at earlier times; thus
the LF of {\gamma}-ray FSRQs follows a luminosity-dependent density evolution
similarly to that of radio-quiet AGN. Also using data from the Swift Burst
Alert Telescope we derive the average spectral energy distribution of FSRQs in
the 10 keV-100 GeV band and show that there is no correlation of the peak
{\gamma}-ray luminosity with {\gamma}-ray peak frequency. The coupling of the
SED and LF allows us to predict that the contribution of FSRQs to the Fermi
isotropic {\gamma}-ray background is 9.3(+1.6/-1.0) (\pm3% systematic
uncertainty) in the 0.1-100GeV band. Finally we determine the LF of unbeamed
FSRQs, finding that FSRQs have an average Lorentz factor of {\gamma} =
11.7(+3.3/-2.2), that most are seen within 5\circ of the jet axis, and that
they represent only ~0.1 % of the parent population.Comment: Submitted to the Astrophysical Journa
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