Capture of Leptophilic Dark Matter in Neutron Stars

Dark matter particles will be captured in neutron stars if they undergo scattering interactions with nucleons or leptons. These collisions transfer the dark matter kinetic energy to the star, resulting in appreciable heating that is potentially observable by forthcoming infrared telescopes. While previous work considered scattering only on nucleons, neutron stars contain small abundances of other particle species, including electrons and muons. We perform a detailed analysis of the neutron star kinetic heating constraints on leptophilic dark matter. We also estimate the size of loop induced couplings to quarks, arising from the exchange of photons and Z bosons. Despite having relatively small lepton abundances, we find that an observation of an old, cold, neutron star would provide very strong limits on dark matter interactions with leptons, with the greatest reach arising from scattering off muons. The projected sensitivity is orders of magnitude more powerful than current dark matter-electron scattering bounds from terrestrial direct detection experiments.Comment: 26 pages, 8 figures, 3 tables, 2 appendices. Discussion extended, references added, matches JCAP published versio

Reducing the fine-tuning of gauge-mediated SUSY breaking

Despite their appealing features, models with gauge-mediated supersymmetry breaking (GMSB) typically present a high degree of fine-tuning, due to the initial absence of the top trilinear scalar couplings, $A_t=0$. In this paper, we carefully evaluate such a tuning, showing that is worse than per mil in the minimal model. Then, we examine some existing proposals to generate $A_t\neq 0$ term in this context. We find that, although the stops can be made lighter, usually the tuning does not improve (it may be even worse), with some exceptions, which involve the generation of $A_t$ at one loop or tree level. We examine both possibilities and propose a conceptually simplified version of the latter; which is arguably the optimum GMSB setup (with minimal matter content), concerning the fine-tuning issue. The resulting fine-tuning is better than one per mil, still severe but similar to other minimal supersymmetric standard model constructions. We also explore the so-called "little $A_t^2/m^2$ problem", i.e. the fact that a large $A_t$-term is normally accompanied by a similar or larger sfermion mass, which typically implies an increase in the fine-tuning. Finally, we find the version of GMSB for which this ratio is optimized, which, nevertheless, does not minimize the fine-tuning.Comment: 16 pages, 11 figures, 1 appendix. Discussion extended, matches EPJC published versio

Local quantum thermometry using Unruh-DeWitt detectors

En este trabajo, proponemos una definición operacional de la temperatura local de un campo cuántico usando detectores Unruh-DeWitt, de forma similar a la empleada en los efectos Unruh y Hawking. Con esta definición, un sistema cuántico inhomogéneo en equilibrio puede tener diferentes temperaturas locales, en analogía con el teorema de Tolman-Ehrenfest en relatividad general. Hemos estudiado la distribución de la temperatura local en el estado fundamental de un sistema fermiónico con términos de hopping en un espacio curvo. La temperatura observada tiende a cero conforme el acoplo termómetrosistema, g, disminuye. Además, para valores pequeños pero finitos de g, mostramos que el producto de la temperatura local observada y el logaritmo de la velocidad local de la luz es aproximadamente constante. Nuestras predicciones son susceptibles de comprobación en sistemas de átomos ultrafríos.We propose an operational definition for the local temperature of a quantum field employing Unruh-DeWitt detectors, as used in the study of the Unruh and Hawking effects. With this definition, an inhomogeneous quantum system in equilibrium can have different local temperatures, in analogy with the Tolman-Ehrenfest theorem from general relativity. We have studied the local temperature distribution on the ground state of hopping fermionic systems on a curved background. The observed temperature tends to zero as the thermometer-system coupling, g, vanishes. Yet, for small but finite values of g, we show that the product of the observed local temperature and the logarithm of the local speed of light is approximately constant. Our predictions should be testable on ultracold atomic systems.Tesi

The naturalness criterion for supersymmetric scenarios

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 28-07-201

What is a Natural SUSY scenario?

The idea of "Natural SUSY", understood as a supersymmetric scenario where the fine-tuning is as mild as possible, is a reasonable guide to explore supersymmetric phenomenology. In this paper, we re-examine this issue in the context of the MSSM including several improvements, such as the mixing of the fine-tuning conditions for different soft terms and the presence of potential extra fine-tunings that must be combined with the electroweak one. We give tables and plots that allow to easily evaluate the fine-tuning and the corresponding naturalness bounds for any theoretical model defined at any high-energy (HE) scale. Then, we analyze in detail the complete fine-tuning bounds for the unconstrained MSSM, defined at any HE scale. We show that Natural SUSY does not demand light stops. Actually, an average stop mass below 800 GeV is disfavored, though one of the stops might be very light. Regarding phenomenology, the most stringent upper bound from naturalness is the one on the gluino mass, which typically sets the present level of fine-tuning at ${\cal O}(1\%)$. However, this result presents a strong dependence on the HE scale. E.g. if the latter is $10^7$ GeV the level of fine-tuning is $\sim$ four times less severe. Finally, the most robust result of Natural SUSY is by far that Higgsinos should be rather light, certainly below 700 GeV for a fine-tuning of ${\cal O}(1\%)$ or milder. Incidentally, this upper bound is not far from $\simeq1$ TeV, which is the value required if dark matter is made of Higgsinos.Comment: 41 pages, 8 figures, 9 tables. References added, matches JHEP published versio

Objects of augmented reality: perceptions of pedagogy students

La Realidad Aumentada (RA) se presenta como una tecnología emergente que ofrece grandes posibilidades a la sociedad en general, y a la formación universitaria en particular, debido a las oportunidades que presenta para crear entornos de aprendizaje atractivos, activos y constructivistas. La investigación que presentamos perseguía conocer la percepción que tienen los alumnos del Grado de Pedagogía sobre las potencialidades y dificultades de esta tecnología en educación, y empoderar al alumnado para que diseñaran contenidos en formato de objetos de RA. Para recabar la información se diseñó un cuestionario compuesto por 23 ítems en escala Likert. La muestra del estudio estuvo formada por 78 estudiantes del 2º curso del Grado de Pedagogía de la Universidad de Sevilla, que cursaban la asignatura Tecnología Educativa. Como resultados de esta investigación, podemos destacar las percepciones positivas que tienen los futuros profesionales de la educación sobre esta tecnología y, especialmente los beneficios que aporta el uso de la misma en los procesos de aprendizaje.Augmented Reality (AR) is presented as an emerging technology that offers great possibilities to society in general, and to university education in particular, due to the opportunities it presents to create learning environments, active and constructivist. The research that we present will seek to know the perception that the students of the Degree of Pedagogy have about the potentialities and difficulties of this technology in education, and empowers the student to design the contents of the RA. To collect the information, a questionnaire was designed consisting of 23 items on a Likert scale. The sample of the study was formed by 78 students of the 2nd year of the Degree of Pedagogy of the University of Seville, who were taking the course Educational Technology. As results of this research, we can highlight the positive perceptions that future professionals of education have about this technology and, especially, the benefits that the use of it provides in the learning processes.Ministerio de Economía y Competitividad EDU2014-57446-