42,178 research outputs found
On the Dark Matter Solutions to the Cosmic Ray Lepton Puzzle
Recent measurements of cosmic ray leptons by PAMELA, ATIC, HESS and Fermi
revealed interesting excesses. Many authors suggested particle Dark Matter (DM)
annihilations could be at the origin of these effects. In this paper, we
critically assess this interpretation by reviewing some results questioning the
naturalness and robustness of such an interpretation. Natural values for the DM
particle parameters lead to a poor leptons production so that models often
require signal enhancement effects that we constrain here. Considering DM
annihilations are likely to produce antiprotons as well, we use the PAMELA
antiproton to proton ratio measurements to constrain a possible exotic
contribution. We also consider the possibility of an enhancement due to a
nearby clump of DM. This scenario appears unlikely when compared to the
state-of-the-art cosmological N-body simulations. We conclude that the bulk of
the observed signals most likely has no link with DM and is rather a new, yet
unconsidered source of background for searches in these channels.Comment: 8 pages, Proceedings of the Invisible Universe International
Conference 2009, Pari
Information structure and the status of np in russian
In his 1995 monograph, Apresyan suggests that it would be extremely interesting to investigate the means of expressing the definiteness/indefiniteness opposition in languages that do not have articles. In this paper, I will attempt to find possible correlations between the organization of discourse and the positions in which the (in)definite nominals may appear within a sentence of Russian. I will examine the information structure of Russian sentences and, based on the previous analyses, provide a new account of their organization with respect to information packaging. I will then look at various nominal elements contained in certain parts of a sentence and arrive at a system describing the distribution of NPs in Russian with respect to the information structure. The ultimate goal of this paper is to establish and motivate a system of correlations between various types of NPs and functions of information structure. This goal will be achieved by determining which characteristic of a NP may serve as a criterion allowing to provide a one-to-one mapping
Seeking particle dark matter in the TeV sky
Under the assumption that dark matter is made of new particles, annihilations
of those are required to reproduce the correct dark matter abundance in the
Universe. This process can occur in dense regions of our Galaxy such as the
Galactic center, dwarf galaxies and other types of sub-haloes. High-energy
gamma-rays are expected to be produced in dark matter particle collisions and
could be detected by ground-based Cherenkov telescopes such as HESS, MAGIC and
VERITAS. The main experimental challenges to get constraints on particle dark
matter models are reviewed, making explicit the pros and cons that are inherent
to this technique, together with the current results from running
observatories. Main results concerning dark matter searches towards selected
targets with Cherenkov telescopes are presented. Eventually, a focus is made on
a new way to perform a search for Galactic subhaloes with such telescopes,
based on wide-field surveys, as well as future prospects.Comment: 12 pages, 10 figures. To appear in the proceedings of the eleventh
international symposium Frontiers of Fundamental Physic
Infinitesimal local operations and differential conditions for entanglement monotones
Much of the theory of entanglement concerns the transformations that are
possible to a state under local operations with classical communication (LOCC);
however, this set of operations is complicated and difficult to describe
mathematically. An idea which has proven very useful is that of the {\it
entanglement monotone}: a function of the state which is invariant under local
unitary transformations and always decreases (or increases) on average after
any local operation. In this paper we look on LOCC as the set of operations
generated by {\it infinitesimal local operations}, operations which can be
performed locally and which leave the state little changed. We show that a
necessary and sufficient condition for a function of the state to be an
entanglement monotone under local operations that do not involve information
loss is that the function be a monotone under infinitesimal local operations.
We then derive necessary and sufficient differential conditions for a function
of the state to be an entanglement monotone. We first derive two conditions for
local operations without information loss, and then show that they can be
extended to more general operations by adding the requirement of {\it
convexity}. We then demonstrate that a number of known entanglement monotones
satisfy these differential criteria. Finally, as an application, we use the
differential conditions to construct a new polynomial entanglement monotone for
three-qubit pure states. It is our hope that this approach will avoid some of
the difficulties in the theory of multipartite and mixed-state entanglement.Comment: 21 pages, RevTeX format, no figures, three minor corrections,
including a factor of two in the differential conditions, the tracelessness
of the matrix in the convexity condition, and the proof that the local purity
is a monotone under local measurements. The conclusions of the paper are
unaffecte
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