1,720,969 research outputs found
Topics in composite models and dark matter phenomenology
Full text linkWe investigate models of composite dark matter in which the dark matter candidate arises naturally as an accidentally stable bound state of a confining dynamics and with observable signatures in a wide variety of experiments. In the first part of the thesis we introduce and explore a new class of models with dark fermions in the adjoint repre- sentation of the confining gauge group. The low energy dynamics and the cosmological history are peculiar and provide a dark matter candidate with properties much different from that of a canonical WIMP. The dark matter is heavy but has a large interaction range and can be tested primarily with indirect searches. In the second part of the thesis we classify and study models of composite dark matter with a strongly interacting chiral dark sector, in which all the mass scales are generated dynamically. In this case the candidate is a SM singlet dark pion with a thermal abundance whose low energy phenomenology can be thoroughly studied through chiral lagrangian techniques. We present an analysis of the low energy phenomenology, compute the radiatively generated masses of the light states and study the cosmological history of the model. The presence of partner states interacting with the SM offers the opportunity to test the model at colliders. In the last part of the thesis we present the phenomenological signatures of the models previously introduced and determine the current bounds. In doing so we also present a strategy to derive a limit on the lifetime of dark matter particles in generic models of particle dark matter from the observation of the 21 cm cosmological signal
Bounds on Dark Matter decay from 21 cm line
No full textThe observation of the cosmic 21-cm spectrum can serve as a probe for Dark Matter properties. We point out that the knowledge of the signal amplitude at a given redshift allows one to put conservative bounds on the DM decay rate which are independent of astrophysical parameters. These limits are valid for the vast majority of DM models, those without extra IGM cooling or additional background radiation. Using the experimental results reported by the EDGES collaboration, we derive bounds that are stronger than the ones derived from other CMB observations and competitive with the ones from indirect detection
Beyond the standard model with strong dynamics
No full textField theoretical extensions of the Standard Model which retain its successful structural features and simplicity are analyzed and characterized. A general classification is provided, in particular, for theories with new strong dynamics where the Dark Matter candidate is an accidentally stable bound state
Gluequark dark matter
Full text linkAbstract We introduce the gluequark Dark Matter candidate, an accidentally stable bound state made of adjoint fermions and gluons from a new confining gauge force. Such scenario displays an unusual cosmological history where perturbative freeze-out is followed by a non-perturbative re-annihilation period with possible entropy injection. When the gluequark has electroweak quantum numbers, the critical density is obtained for masses as large as PeV. Independently of its mass, the size of the gluequark is determined by the confinement scale of the theory, leading at low energies to annihilation rates and elastic cross sections which are large for particle physics standards and potentially observable in indirect detection experiments
An analytic approach to quasinormal modes for coupled linear systems
Full text linkQuasinormal modes describe the ringdown of compact objects deformed by small
perturbations. In generic theories of gravity that extend General Relativity,
the linearized dynamics of these perturbations is described by a system of
coupled linear differential equations of second order. We first show, under
general assumptions, that such a system can be brought to a Schr\"odinger-like
form. We then devise an analytic approximation scheme to compute the spectrum
of quasinormal modes. We validate our approach using a toy model with a
controllable mixing parameter and showing that the analytic
approximation for the fundamental mode agrees with the numerical computation
when the approximation is justified. The accuracy of the analytic approximation
is at the (sub-) percent level for the real part and at the level of a few
percent for the imaginary part, even when is of order one. Our
approximation scheme can be seen as an extension of the approach of Schutz and
Will to the case of coupled systems of equations, although our approach is not
phrased in terms of a WKB analysis, and offers a new viewpoint even in the case
of a single equation.Comment: 30 pages. v2: matches published versio
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Study the effect of beam energy spread and detector resolution on the search for Higgs boson decays to invisible particles at a future e e circular collider
Full text linkWe study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular collider (FCC-ee) in the process with ( or ) using an integrated luminosity of 3.5 ab at a center-of-mass energy GeV. The impact of the energy spread of the FCC-ee beam and of the resolution in the reconstruction of the leptons is discussed. The minimum branching ratio for a observation after 3.5 ab of data taking is . The branching ratio exclusion limit at 95% CL is .We study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular \epem collider (FCC-ee) in the process with ( or ) using an integrated luminosity of 3.5 ab at a center-of-mass energy GeV. The impact of the energy spread of the FCC-ee beam and of the resolution in the reconstruction of the leptons is discussed. %Two different detector concepts are considered: a detector corresponding to the CMS reconstruction performances and the expected design of the ILC detector. The minimum branching ratio for a observation after 3.5ab of data taking is . The branching ratio exclusion limit at 95\% CL is
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