111 research outputs found
Theories in More than Four Dimensions
Particle physics models where there are large hidden extra dimensions are
currently on the focus of an intense activity. The main reason is that these
large extra dimensions may come with a TeV scale for quantum gravity (or string
theory) which leads to a plethora of new observable phenomena in colliders as
well in other areas of particle physics. Those new dimensions could be as large
as millimeters implying deviations of the Newton's law of gravity at these
scales. Intending to provide a basic introduction to this fast developing area,
we present a general overview of theories with large extra dimensions. We
center our discussion on models for neutrino masses, high dimensional
extensions of the Standard Model and gauge coupling unification. We discuss the
recently proposed technic of splitting fermion wave functions on a tick brane
which may solve the problem of a fast proton decay and produce fermion mass
hierarchies without invoking extra global symmetries. Randall-Sundrum model and
some current trends are also commented.Comment: LaTeX file, 31 pages, no figures. Minor changes, References added.
Lectures given at the IX Mexican School on Particles and Fields, Metepec,
Puebla, Mexico, August, 2000. To appear in the proceeding
GUTs and String-GUTs
We look for a connection between string theories and Grand Unified Theories
(GUTs), with the aim to look for new insights in the existing four dimensional
string-GUT problems. We argue that the construction of consistent string-GUT
models could require the use of non canonical affine levels. We list the most
common level values related to realistic GUTs.Comment: 8 pages, Latex file, no figures. Acepted for publication in
Europhysics Letter
Effects of Lorentz invariance violation on cosmic ray photon emission and gamma ray decay processes
In this work, we use Lorentz invariance violation (LIV) introduced as a
generic modification to particle dispersion relations to study some
consequences of single photon emission, known as vacuum Cherenkov radiation,
and photon decay processes in cosmic and gamma rays. These processes are
forbidden in a Lorentz invariant theory but allowed under the hypothesis of
LIV. We show that the emission rate have a dependency on the cosmic ray primary
mass and the electric charge that could modify the UHECR spectrum. Furthermore,
LIV dramatically enhances photon decay into an electro-positron pair above
certain energy threshold. This last effect can then be used to set limits to
the LIV energy scale from the direct observation of very high energy cosmic
photon events by telescopes of gamma-rays.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Busan, Kore
Radion Cosmology in Theories with Universal Extra Dimensions
We discuss cosmology of models with universal extra dimensions, where the
Standard Model degrees of freedom live in a dimensional brane, with
compact and small extra spatial dimensions. In these models, the simplest way
to obtain the conventional 4-dimensional Planck scale starting with a low
string scale is to have also some larger extra dimensions, where only gravity
propagates. In such theories, dimensional reduction generically leads to at
least two radion fields, one associated with the total volume of the extra
spatial dimensions, and the other with the ratio of the sizes of small and
large extra dimensions. In this paper, we discuss the impact of the radion
fields on cosmology. We emphasize various aspects of radion physics such as
radion coupling to the Standard Model fields, bare and dressed radion masses
during inflation, dynamical stabilization of radions during and after
inflation, radion decay life time and its late dominance in thermal history of
the Universe as well as its quantum fluctuations during inflation. We argue
that models where the radion plays the role of an inflaton or the inflaton is a
brane scalar field, run into problems. We then present a successful inflation
model with bulk scalar fields that seems to have all the desired properties. We
also briefly discuss the possibility of radion as a cold dark matter candidate.Comment: 37 pages + 3 figure
- …