66 research outputs found
Phenomenology of the 1/N Expansion for Field Theories in Extra Dimensions
In this paper we review the properties of the 1/ expansion in
multidimensional theories. Contrary to the usual perturbative expansion it is
renormalizable and contains only logarithmic divergencies. The price for it is
the presence of ghost states which, however, in certain cases do not contribute
to physical amplitudes. In this case the theory is unitary and one can
calculate the cross-sections. As an example we consider the differential cross
section of elastic scattering in -dimensional world. We
look also for the unification of the gauge couplings in multidimensional
Standard Model and its SUSY extension which takes place at energies lower than
in 4 dimensions.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 4 eps figures +
3 axodraw figure
A 5D non compact and non Ricci flat Kaluza-Klein Cosmology
A model universe is proposed in the framework of 5-dimensional noncompact
Kaluza-Klein cosmology which is not Ricci flat. The 4D part as the
Robertson-Walker metric is coupled to conventional perfect fluid, and its
extra-dimensional part is coupled to a dark pressure through a scalar field. It
is shown that neither early inflation nor current acceleration of the 4D
universe would happen if the non-vacuum states of the scalar field would
contribute to 4D cosmology.Comment: 13 pages, major revision, published online in GR
Evaluating Lifeworld as an emancipatory methodology
Disability research is conducted within a highly politicised âhotbedâ of competing paradigms and principles. New researchers, who want to work within the social model, are soon faced with complex and challenging methodological and philosophical dilemmas. The social model advocates research agendas that are focused on the emancipation and empowerment of disabled people but, in reality, these are rarely achieved. To be successful researchers need to engage with innovative and creative methodologies and to share their experiences of these within environments that welcome challenge and debate. This paper focuses on Lifeworld and assesses its value as a tool for emancipatory research. Using examples from a study with parents, whose children were in the process of being labelled as having autism, the paper illustrates how the principles that âunderpinâ the methodology offered a supportive framework for a novice researcher
Nonlinear multidimensional cosmological models with form fields: stabilization of extra dimensions and the cosmological constant problem
We consider multidimensional gravitational models with a nonlinear scalar
curvature term and form fields in the action functional. In our scenario it is
assumed that the higher dimensional spacetime undergoes a spontaneous
compactification to a warped product manifold. Particular attention is paid to
models with quadratic scalar curvature terms and a Freund-Rubin-like ansatz for
solitonic form fields. It is shown that for certain parameter ranges the extra
dimensions are stabilized. In particular, stabilization is possible for any
sign of the internal space curvature, the bulk cosmological constant and of the
effective four-dimensional cosmological constant. Moreover, the effective
cosmological constant can satisfy the observable limit on the dark energy
density. Finally, we discuss the restrictions on the parameters of the
considered nonlinear models and how they follow from the connection between the
D-dimensional and the four-dimensional fundamental mass scales.Comment: 21 pages, LaTeX2e, minor changes, improved references, fonts include
Brane matter, hidden or mirror matter, their various avatars and mixings: many faces of the same physics
Numerous papers deal with the phenomenology related to photon-hidden photon
kinetic mixing and with the effects of a mass mixing on particle-hidden
particle oscillations. In addition, recent papers underline the existence of a
geometrical mixing between branes which would allow a matter swapping between
branes. These approaches and their phenomenologies are reminiscent of each
other but rely on different physical concepts. In the present paper, we suggest
there is no rivalry between these models, which are probably many faces of the
same physics. We discuss some phenomenological consequences of a global
framework.Comment: 9 pages. Typo corrected. Published in European Physical Journal
Cosmological consequences of a Chaplygin gas dark energy
A combination of recent observational results has given rise to what is
currently known as the dark energy problem. Although several possible
candidates have been extensively discussed in the literature to date the nature
of this dark energy component is not well understood at present. In this paper
we investigate some cosmological implications of another dark energy candidate:
an exotic fluid known as the Chaplygin gas, which is characterized by an
equation of state , where is a positive constant. By assuming
a flat scenario driven by non-relativistic matter plus a Chaplygin gas dark
energy we study the influence of such a component on the statistical properties
of gravitational lenses. A comparison between the predicted age of the universe
and the latest age estimates of globular clusters is also included and the
results briefly discussed. In general, we find that the behavior of this class
of models may be interpreted as an intermediary case between the standard and
CDM scenarios.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
CP Asymmetries in B_s Decays and Spontaneous CP violation
We study possible effects of new physics in CP asymmetries in two-body
decays in left-right models with spontaneous CP violation. Considering the
contributions of new CP phases to the mixing as well as to the penguin
dominated decay amplitudes we show that, with the present constraints, large
deviations from the standard model predictions in CP asymmetries are allowed in
both cases. Detection of the new physics can be done by measuring non-zero
asymmetries which are predicted to vanish in the standard model or by comparing
two measurements which are predicted to be equal in the standard model. In
particular, we show that the measurement of the CKM angle in
electroweak penguin dominated processes
can largely be affected by the new physics.Comment: References and discussion added, version to be published in PR
Analysis of fish assemblages in sectors along a salinity gradient based on species, families and functional groups
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