3,909 research outputs found
Light charged Higgs boson production at the Large Hadron electron Collider
We study the production of a light charged Higgs boson at the future Large
Hadron electron Collider (LHeC), through the process
considering both decay channels and in the final state. We analyse these processes in the context of the
2-Higgs Doublet Model Type III (2HDM-III) and assess the LHeC sensitivity to
such signals against a variety of both reducible and irreducible
backgrounds. We confirm that prospects for detection in the 2HDM-III are
excellent assuming standard collider energy and luminosity conditions.Comment: 12 pages, 12 figures. Accepted in Physical Review
Isocausal spacetimes may have different causal boundaries
We construct an example which shows that two isocausal spacetimes, in the
sense introduced by Garc\'ia-Parrado and Senovilla, may have c-boundaries which
are not equal (more precisely, not equivalent, as no bijection between the
completions can preserve all the binary relations induced by causality). This
example also suggests that isocausality can be useful for the understanding and
computation of the c-boundary.Comment: Minor modifications, including the title, which matches now with the
published version. 12 pages, 3 figure
Further properties of causal relationship: causal structure stability, new criteria for isocausality and counterexamples
Recently ({\em Class. Quant. Grav.} {\bf 20} 625-664) the concept of {\em
causal mapping} between spacetimes --essentially equivalent in this context to
the {\em chronological map} one in abstract chronological spaces--, and the
related notion of {\em causal structure}, have been introduced as new tools to
study causality in Lorentzian geometry. In the present paper, these tools are
further developed in several directions such as: (i) causal mappings --and,
thus, abstract chronological ones-- do not preserve two levels of the standard
hierarchy of causality conditions (however, they preserve the remaining levels
as shown in the above reference), (ii) even though global hyperbolicity is a
stable property (in the set of all time-oriented Lorentzian metrics on a fixed
manifold), the causal structure of a globally hyperbolic spacetime can be
unstable against perturbations; in fact, we show that the causal structures of
Minkowski and Einstein static spacetimes remain stable, whereas that of de
Sitter becomes unstable, (iii) general criteria allow us to discriminate
different causal structures in some general spacetimes (e.g. globally
hyperbolic, stationary standard); in particular, there are infinitely many
different globally hyperbolic causal structures (and thus, different conformal
ones) on , (iv) plane waves with the same number of positive eigenvalues
in the frequency matrix share the same causal structure and, thus, they have
equal causal extensions and causal boundaries.Comment: 33 pages, 9 figures, final version (the paper title has been
changed). To appear in Classical and Quantum Gravit
Delocalization in Continuous Disordered Systems
Continuous One-dimensional models supporting extended states are studied.
These delocalized statesoccur at well defined values of the energy and are
consequences of simple statistical correlation rules. We explicitly study
alloys of delta-barrier potentials as well as alloys and liquids of quantum
well as.The divergence of the localization length is studied and a critical
exponent 2/3 is found for the delta-barrier case, whereas for the quantum wells
we find an exponent of 2 or 2/3 depending on the well's parameters. These
results support the idea that correlations between random scattering sequences
break Anderson localization. We further calculate the conductance of disordered
superlattices. At the peak transmission the relative fluctuations of the
transmission coefficient are vanishing.Comment: 8 page
Three-dimensional effects on extended states in disordered models of polymers
We study electronic transport properties of disordered polymers in the
presence of both uncorrelated and short-range correlated impurities. In our
procedure, the actual physical potential acting upon the electrons is replaced
by a set of nonlocal separable potentials, leading to a Schr\"odinger equation
that is exactly solvable in the momentum representation. We then show that the
reflection coefficient of a pair of impurities placed at neighboring sites
(dimer defect) vanishes for a particular resonant energy. When there is a
finite number of such defects randomly distributed over the whole lattice, we
find that the transmission coefficient is almost unity for states close to the
resonant energy, and that those states present a very large localization
length. Multifractal analysis techniques applied to very long systems
demonstrate that these states are truly extended in the thermodynamic limit.
These results reinforce the possibility to verify experimentally theoretical
predictions about absence of localization in quasi-one-dimensional disordered
systems.Comment: 16 pages, REVTeX 3.0, 5 figures on request from FDA
([email protected]). Submitted to Phys. Rev. B. MA/UC3M/09/9
One-loop effects of extra dimensions on the WW\gamma and WWZ vertices
The one-loop contribution of the excited Kaluza-Klein (KK) modes of the
gauge group on the off-shell and vertices is
calculated in the context of a pure Yang-Mills theory in five dimensions and
its phenomenological implications discussed. The use of a gauge-fixing
procedure for the excited KK modes that is covariant under the standard gauge
transformations of the group is stressed. A gauge-fixing term and the
Faddeev-Popov ghost sector for the KK gauge modes that are separately invariant
under the standard gauge transformations of are presented. It is
shown that the one-loop contributions of the KK modes to the off-shell
and vertices are free of ultraviolet divergences and
well-behaved at high energies. It is found that for a size of the fifth
dimension of , the one-loop contribution of the KK modes to
these vertices is about one order of magnitude lower than the corresponding
standard model radiative correction. This contribution is similar to the one
estimated for new gauge bosons contributions in other contexts. Tree-level
effects on these vertices induced by operators of higher canonical dimension
are also investigated. It is found that these effects are lower than those
generated at the one-loop order by the KK gauge modes.Comment: 19 pages, 9 figures. Some typos were correcte
Abuse and discrimination towards indigenous people in public health care facilities: experiences from rural Guatemala
Background Health inequalities disproportionally affect indigenous people in Guatemala. Previous studies have noted that the disadvantageous situation of indigenous people is the result of complex and structural elements such as social exclusion, racism and discrimination. These elements need to be addressed in order to tackle the social determinants of health. This research was part of a larger participatory collaboration between Centro de Estudios para la Equidad y Gobernanza en los Servicios de Salud (CEGSS) and community based organizations aiming to implement social accountability in rural indigenous municipalities of Guatemala. Discrimination while seeking health care services in public facilities was ranked among the top three problems by communities and that should be addressed in the social accountability intervention. This study aimed to understand and categorize the episodes of discrimination as reported by indigenous communities. Methods A participatory approach was used, involving CEGSS’s researchers and field staff and community leaders. One focus group in one rural village of 13 different municipalities was implemented. Focus groups were aimed at identifying instances of mistreatment in health care services and documenting the account of those who were affected or who witnessed them. All of the 132 obtained episodes were transcribed and scrutinized using a thematic analysis. Results Episodes described by participants ranged from indifference to violence (psychological, symbolic, and physical), including coercion, mockery, deception and racism. Different expressions of discrimination and mistreatment associated to poverty, language barriers, gender, ethnicity and social class were narrated by participants. Conclusions Addressing mistreatment in public health settings will involve tackling the prevalent forms of discrimination, including racism. This will likely require profound, complex and sustained interventions at the programmatic and policy levels beyond the strict realm of public health services. Future studies should assess the magnitude of the occurrence of episodes of maltreatment and racism within indigenous areas and also explore the providers’ perceptions about the problem
Extended States in a One-dimensional Generalized Dimer Model
The transmission coefficient for a one dimensional system is given in terms
of Chebyshev polynomials using the tight-binding model. This result is applied
to a system composed of two impurities located between sites of a host
lattice. It is found that the system has extended states for several values of
the energy. Analytical expressions are given for the impurity site energy in
terms of the electron's energy. The number of resonant states grows like the
number of host sites between the impurities. This property makes the system
interesting since it is a simple task to design a configuration with resonant
energy very close to the Fermi level .Comment: 4 pages, 3 figure
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