1,721,110 research outputs found
WIMP dark matter as an active component
No full textIn these proceedings I briefly review the main mechanisms by means of which Weakly Interacting Massive Particles, here assumed to constitute Dark Matter, can contribute beyond the pure gravitational interaction to the evolution of the Universe. In particular, I will comment on how they can modify the yields of Primordial Nucleosynthesis, alter the Reionization history and take part into the first stellar episode in the Universe. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial- ShareAlike Licence
Constraining Dark Matter through CMB
No full textSelf-Annihilating Dark Matter (DM) candidates can modify the recombination history of the Universe, injecting additional energy into the thermal gas, and modifying its ionization state. The electron fraction history affects the CMB temperature and polarization power spectra; observations of the modifications (or of the absence) of the latter can then be used to constrain the power injected by annihilating DM, and ultimately the DM parameters themselves. DM annihilations able to modify the CMB spectra are active at redshifts 100 ×z× 1000, thus involving only a smooth density field, and permitting to ignore structure formation. Current WMAP7 data on the TT, TE and EE angular power spectra already permit to rule out interesting regions in the 〈σv〉 -mx space; the forthcoming PLANCK ones will permit to explore the "thermal WIMP" region. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution- NonCommercial-ShareAlike Licence
WIMP dark matter and the first stars
No full textIf weakly interactingmassive particles (WIMPs) constitute the bulk of darkmatter (DM), energy from the self-annihilation of these particles can affect Population III (Pop III) star formation via two mechanisms. Before the protostar forms, energy from DM annihilations can couple to primordial gas chemistry and slightly alter the properties of the cloud-without, however, inducing dramatic changes in the final mass of the star. Later, scattering betweenWIMPs and baryons within the protostar can in principle congregate enough DMfor annihilations, rather than nuclear reactions, to support the star against gravity. In these proceedings I briefly summarize the state of the art of the field, as well the prospects for observing such stars. © 2010 American Institute of Physics
Self-annihilating dark matter and the CMB: Reionizing the universe and constraining cross sections
No full textI summarize the recent advances in determining the effects of self-ahhinilating WIMP dark matter on the modification of the recombination history, at times earlier than the formation of astrophysical objects. Depending on mass and self-annihilation cross section, WIMP DM can reproduce sizable amounts of the total free electron abundance at z≳6; as known, this affects the CMB temperature and polarization correlation spectra, and can be used to place stringent bounds in the particle mass vs cross-section plane. WMAP5 data already strongly disfavor the region capable to explain the recent positron anomaly in terms of DM annihilation, whereas in principle the Planck mission has the potential to see a signal produced by a candidate in that region, or from WIMPs with thermal annihilation cross-sections 〈σν〉∼ 3×10-26cm3/s and masses with values m κ≲50GeV/c2. © 2010 American Institute of Physics
WIMP dark matter and the first stars: A critical overview
No full textIf Dark Matter (DM) is composed by Weakly Interacting Massive Particles, its annihilation in the halos harboring the earliest star formation episode may strongly influence the first generation of stars (Population III). Whereas DM annihilation at early stages of gas collapse does not dramatically affect the properties of the cloud, the formation of a hydrostatic object (protostar) and its evolution toward the main sequence may be delayed. This process involves DM concentrated in the center of the halo by gravitational drag, and no consensus is yet reached over whether this can push the initial mass of Population III to higher masses. DM can also be captured through scattering over the baryons in a dense object, onto or very close to the Main Sequence. This mechanism can affect formed stars and in principle prolonge their lifetimes. The strength of both mechanisms depends upon several environmental conditions and on DM parameters; such spread in the parameter space leads to very different scenarios for the observables in the Population. Here I summarize the state of the art in modelling and observational expectations, eventually highlighting the most critical assumptions and reasons of uncertainty
The lithium problem: A phenomenologist's perspective
No full textThirty years after the first observation of the 7Li isotope in the atmosphere of metal-poor halo stars, the puzzle about its origin persists. Do current observations still support the existence of a "plateau": a single value of lithium abundance, constant over several orders of magnitude in the metallicity of the target star? If this plateau exists, is it universal in terms of observational loci of target stars? Is it possible to explain such observations with known astrophysical processes? Can yet poorly explored astrophysical mechanisms explain the observations or do we need to invoke physics beyond the standard model of Cosmology and/or the standard model of Particle Physics to explain them? Is there a 6Li problem, and is it connected to the 7Li one? These questions have been discussed at the Paris workshop "Lithium in the Cosmos", and I summarize here its contents, providing an overview from the perspective of a phenomenologist
Neutrino Background from Population III Stars
No full textPopulation III Stars (PopIII) are the first generation of stars formed from the collapse of the very first structures in the Universe. Their peculiar chemical composition (metal-free, resembling the Primordial Nucleosynthesis yields) affects their formation and evolution and makes them unusually big and hot stars. They are good candidates for the engines of Reionization of the Universe although their direct observation is extremely difficult. Here we summarize a study of their expected diffuse low-energy neutrino background flux at Earth. © 2011
First stars and WIMP dark matter: A state of the art review
No full textIt has been suggested that Weakly Interacting Massive Particles (WIMPs) may significantly alter the formation and evolution of the First Stars, if the Dark Matter (DM) is actually made of such particles. In these proceedings I summarize the state of the art of the last five years of research in this field. © 2012 American Institute of Physics
Lithium synthesis around stellar mass black holes
No full textWe present a study of nucleosynthesis of light elements in the accretion disk of stellar mass black holes. The amount of both stable isotopes of lithium produced is sizeable for a host of values of black hole mass, disk viscosity and accretion rate. We discuss our results in the context of the lithium problem and propose observational tests for this mechanism
Mapping dark matter in the Milky Way, a synopsis
No full textMapping the dark matter distribution across our Galaxy represents a central challenge for the near future as a new generation of space-borne and ground-based astronomical surveys swiftly comes online. Here we present a synopsis of the present status of the field, reviewing briefly the baryonic content and the kinematics of the MilkyWay and outlining the methods used to infer the dark matter component. The discussion then proceeds with some of the latest developments based on our own work. In particular, we present a new compilation of kinematic measurements tracing the rotation curve of the Galaxy and an exhaustive array of observation-based baryonic models setting the contribution of stellar bulge, stellar disc and gas to the total gravitational potential. The discrepancy between these two components is then quantified to derive the latest constraints on the dark matter distribution and on modified Newtonian dynamics. We shall end with an overview of future directions to improve our mapping of the dark matter distribution in the Milky Way
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