959 research outputs found
Gamma-ray lines and One-Loop Continuum from s-channel Dark Matter Annihilations
The era of indirect detection searches for dark matter has begun, with the
sensitivities of gamma-ray detectors now approaching the parameter space
relevant for weakly interacting massive particles. In particular, gamma ray
lines would be smoking gun signatures of dark matter annihilation, although
they are typically suppressed compared to the continuum. In this paper, we pay
particular attention to the 1-loop continuum generated together with the
gamma-ray lines and investigate under which conditions a dark matter model can
naturally lead to a line signal that is relatively enhanced. We study generic
classes of models in which DM is a fermion that annihilates through an
s-channel mediator which is either a vector or scalar and identify the coupling
and mass conditions under which large line signals occur. We focus on the
"forbidden channel mechanism" advocated a few years ago in the "Higgs in space"
scenario for which tree level annihilation is kinematically forbidden today.
Detailed calculations of all 1-loop annihilation channels are provided. We
single out very simple models with a large line over continuum ratio and
present general predictions for a large range of WIMP masses that are relevant
not only for Fermi and Hess II but also for the next generation of telescopes
such as CTA and Gamma-400. Constraints from the relic abundance, direct
detection and collider bounds are also discussed.Comment: 32 pages, 13 figures; v2: minor clarifications, summary paragraph
added; v3: matches published version, minor clarifications, results unchange
The WIMP Forest: Indirect Detection of a Chiral Square
The spectrum of photons arising from WIMP annihilation carries a detailed
imprint of the structure of the dark sector. In particular, loop-level
annihilations into a photon and another boson can in principle lead to a series
of lines (a WIMP forest) at energies up to the WIMP mass. A specific model
which illustrates this feature nicely is a theory of two universal extra
dimensions compactified on a chiral square. Aside from the continuum emission,
which is a generic prediction of most dark matter candidates, we find a
"forest" of prominent annihilation lines that, after convolution with the
angular resolution of current experiments, leads to a distinctive (2-bump plus
continuum) spectrum, which may be visible in the near future with the Fermi
Gamma-Ray Space Telescope (formerly known as GLAST).Comment: 11 pages, 4 figure
New insights into the size and stoichiometry of the plasminogen activator inhibitor type-1·vitronectin complex
Plasminogen activator inhibitor-type 1 (PAI-1) is the primary inhibitor of endogenous plasminogen activators that generate plasmin in the vicinity of a thrombus to initiate thrombolysis, or in the pericellular region of cells to facilitate migration and/or tissue remodeling. It has been shown that the physiologically relevant form of PAI-1 is in a complex with the abundant plasma glyco-protein, vitronectin. The interaction between vitronectin and PAI-1 is important for stabilizing the inhibitor in a reactive conformation. Although the complex is clearly significant, information is vague regarding the composition of the complex and consequences of its formation on the distribution and activity of vitronectin in vivo. Most studies have assumed a 1:1 interaction between the two proteins, but this has not been demonstrated experimentally and is a matter of some controversy since more than one PAI-1-binding site has been proposed within the sequence of vitronectin. To address this issue, competition studies using monoclonal antibodies specific for separate epitopes confirmed that the two distinct PAI-1-binding sites present on vitronectin can be occupied simultaneously. Analytical ultracentrifugation was used also for a rigorous analysis of the composition and sizes of complexes formed from purified vitronectin and PAI-1. The predominant associating species observed was high in molecular weight (M(r) ~ 320,000), demonstrating that self-association of vitronectin occurs upon interaction with PAI-1. Moreover, the size of this higher order complex indicates that two molecules of PAI-1 bind per vitronectin molecule. Binding of PAI-1 to vitronectin and association into higher order complexes is proposed to facilitate interaction with macromolecules on surfaces
Gamma Rays from Top-Mediated Dark Matter Annihilations
Lines in the energy spectrum of gamma rays are a fascinating experimental
signal, which are often considered "smoking gun" evidence of dark matter
annihilation. The current generation of gamma ray observatories are currently
closing in on parameter space of great interest in the context of dark matter
which is a thermal relic. We consider theories in which the dark matter's
primary connection to the Standard Model is via the top quark, realizing strong
gamma ray lines consistent with a thermal relic through the forbidden channel
mechanism proposed in the Higgs in Space Model. We consider realistic
UV-completions of the Higgs in Space and related theories, and show that a rich
structure of observable gamma ray lines is consistent with a thermal relic as
well as constraints from dark matter searches and the LHC. Particular attention
is paid to the one loop contributions to the continuum gamma rays, which can
easily swamp the line signals in some cases, and have been largely overlooked
in previous literature.Comment: 24 pages, 16 figures; v2: matches published version, one figure added
in Section 3 for clarification, results unchange
High energy neutrinos from neutralino annihilations in the Sun
Neutralino annihilations in the Sun to weak boson and top quark pairs lead to
high-energy neutrinos that can be detected by the IceCube and KM3 experiments
in the search for neutralino dark matter. We calculate the neutrino signals
from real and virtual WW, ZZ, Zh, and production and decays,
accounting for the spin-dependences of the matrix elements, which can have
important influences on the neutrino energy spectra. We take into account
neutrino propagation including neutrino oscillations, matter-resonance,
absorption, and nu_tau regeneration effects in the Sun and evaluate the
neutrino flux at the Earth. We concentrate on the compelling Focus Point (FP)
region of the supergravity model that reproduces the observed dark matter relic
density. For the FP region, the lightest neutralino has a large bino-higgsino
mixture that leads to a high neutrino flux and the spin-dependent neutralino
capture rate in the Sun is enhanced by 10^3 over the spin-independent rate. For
the standard estimate of neutralino captures, the muon signal rates in IceCube
are identifiable over the atmospheric neutrino background for neutralino masses
above M_Z up to 400 GeV.Comment: 45 pages, 18 figures and 5 tables, PRD versio
Come to Daddy? Claiming Chris Cunningham for British Art Cinema
Twenty years after he came to prominence via a series of provocative, ground-breaking music videos, Chris Cunningham remains a troubling, elusive figure within British visual culture. His output – which includes short films, advertisements, art gallery commissions, installations, music production and a touring multi-screen live performance – is relatively slim, and his seemingly slow work rate (and tendency to leave projects uncompleted or unreleased) has been a frustration for fans and commentators, particularly those who hoped he would channel his interests and talents into a full-length ‘feature’ film project. There has been a diverse critical response to his musical sensitivity, his associations with UK electronica culture – and the Warp label in particular – his working relationship with Aphex Twin, his importance within the history of the pop video and his deployment of transgressive, suggestive imagery involving mutated, traumatised or robotic bodies. However, this article makes a claim for placing Cunningham within discourses of British art cinema. It proposes that the many contradictions that define and animate Cunningham's work – narrative versus abstraction, political engagement versus surrealism, sincerity versus provocation, commerce versus experimentation, art versus craft, a ‘British’ sensibility versus a transnational one – are also those that typify a particular terrain of British film culture that falls awkwardly between populism and experimentalism
Neutron time-of-flight measurements of charged-particle energy loss in inertial confinement fusion plasmas
Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4  keV and particle densities of n≈(12-2)×10^{24}  cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data
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