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Sub-GeV Dark Matter Shining at Future MeV γ -Ray Telescopes
Full text linkWe propose a novel framework where light (sub-GeV) dark matter (DM) is detectable with future MeV γ-ray telescopes without conflicting with cosmic microwave background (CMB) data. The stable DM particle χ has a very low thermal relic abundance due to its large pair-annihilation cross section. The DM number density is stored in a slightly heavier, metastable partner ψ with suppressed pair-annihilation rates, that does not perturb the CMB, and whose late-time decays ψ→χ fill the Universe with χ DM particles. We provide explicit, model-independent realizations for this framework, and discuss constraints on late-time decays, and thus on parameters of this setup, from CMB, big bang nucleosynthesis, and large scale structure
Neutralino cold dark matter in a one-parameter extension of the minimal supergravity model
No full textWithin the minimal supergravity model (mSUGRA) framework, the expectation for the relic density of neutralinos exceeds the WMAP determination, unless neutralinos (a) have a significant Higgsino component, (b) have a mass close to half that of a heavy Higgs boson, or (c) can efficiently coannihilate with a charged or colored particle. Within a one-parameter extension of the mSUGRA model which includes nonuniversal Higgs masses, we show that agreement with the WMAP data can be obtained over a wide range of mSUGRA parameters for scenarios (a) and (b), so that the phenomenological implications may be much more diverse than in mSUGRA. We show that direct and/or indirect detection of neutralino dark matter should be possible at various current and planned facilities.<br/
Dark matter inelastic up-scattering with the interstellar plasma: A new source of x-ray lines, including at 3.5 keV DARK MATTER INELASTIC UP-SCATTERING with the ... D'ERAMO et al
Full text linkWe explore the phenomenology of a class of models where the dark matter
particle can inelastically up-scatter to a heavier excited state via
off-diagonal dipolar interactions with the interstellar plasma (gas or free
electrons). The heavier particle then rapidly decays back to the dark matter
particle plus a quasi-monochromatic photon. For the process to occur at
appreciable rates, the mass splitting between the heavier state and the dark
matter must be comparable to, or smaller than, the kinetic energy of particles
in the plasma. As a result, the predicted photon line falls in the soft X-ray
range, or, potentially, at arbitrarily lower energies. We explore experimental
constraints from cosmology and particle physics, and present accurate
calculations of the dark matter thermal relic density and of the flux of
monochromatic X-rays from thermal plasma excitation. We find that the model
provides a natural explanation for the observed 3.5 keV line from clusters of
galaxies and from the Galactic center, and is consistent with null detections
of the line from dwarf galaxies. The unique line shape, which will be resolved
by future observations with the Hitomi (formerly Astro-H) satellite, and the
predicted unique morphology and target-temperature dependence will enable easy
discrimination of this class of models versus other scenarios for the
generation of the 3.5 keV line or of any other unidentified line across the
electromagnetic spectrum
When the universe expands too fast: Relentless dark matter
Full text linkWe consider a modification to the standard cosmological history consisting of
introducing a new species whose energy density red-shifts with the scale
factor like . For n>0, such a red-shift is
faster than radiation, hence the new species dominates the energy budget of the
universe at early times while it is completely negligible at late times. If
equality with the radiation energy density is achieved at low enough
temperatures, dark matter can be produced as a thermal relic during the new
cosmological phase. Dark matter freeze-out then occurs at higher temperatures
compared to the standard case, implying that reproducing the observed abundance
requires significantly larger annihilation rates. Here, we point out a
completely new phenomenon, which we refer to as dark
matter: for large enough , unlike the standard case where annihilation ends
shortly after the departure from thermal equilibrium, dark matter particles
keep annihilating long after leaving chemical equilibrium, with a significant
depletion of the final relic abundance. Relentless annihilation occurs for and for s-wave and p-wave annihilation, respectively, and it
thus occurs in well motivated scenarios such as a quintessence with a kination
phase. We discuss a few microscopic realizations for the new cosmological
component and highlight the phenomenological consequences of our calculations
for dark matter searches
Dark Matter Freeze-in Production in Fast-Expanding Universes
Full text linkIf the dark matter is produced in the early universe prior to Big Bang
nucleosynthesis, a modified cosmological history can drastically affect the
abundance of relic dark matter particles. Here, we assume that an additional
species to radiation dominates at early times, causing the expansion rate at a
given temperature to be larger than in the standard radiation-dominated case.
We demonstrate that, if this is the case, dark matter production via freeze-in
(a scenario when dark matter interacts very weakly, and is dumped in the early
universe out of equilibrium by decay or scattering processes involving
particles in the thermal bath) is dramatically suppressed. We illustrate and
quantitatively and analytically study this phenomenon for three different
paradigmatic classes of freeze-in scenarios. For the frozen-in dark matter
abundance to be as large as observations, couplings between the dark matter and
visible-sector particles must be enhanced by several orders of magnitude. This
sheds some optimistic prospects for the otherwise dire experimental and
observational outlook of detecting dark matter produced by freeze-in
Singlet scalar dark matter: Monochromatic gamma rays and metastable vacua
No full textWe calculate the pair-annihilation cross section of real scalar singlet dark matter into two monoenergetic photons. We derive constraints on the theory parameter space from the Fermi limits on gamma-ray lines, and we compare with current limits from direct dark matter detection. We show that the new limits, albeit typically relevant only when the dark matter mass is close to half the standard model Higgs mass, rule out regions of the theory parameter space that are otherwise not constrained by other observations or experiments. In particular, the new excluded regions partly overlap with the parameter space where real scalar singlet dark matter might explain the anomalous signals observed by CDMS. We also calculate the lifetime of unstable vacuum configurations in the scalar potential, and show that the gamma-ray limits are quite relevant in regions where the electroweak vacuum is metastable with a lifetime longer than the age of the Universe. © 2010 The American Physical Society
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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