11 research outputs found
Geometric Origin of CP Violation in an Extra-Dimensional Brane World
The fermion mass hierarchy and finding a predictive mechanism of the flavor
mixing parameters remain two of the least understood puzzles facing particle
physics today. In this work, we demonstrate how the realization of the Dirac
algebra in the presence of two extra spatial dimensions leads to complex
fermion field profiles in the extra dimensions. Dimensionally reducing to four
dimensions leads to complex quark mass matrices in such a fashion that CP
violation necessarily follows. We also present the generalization of the
Randall-Sundrum scenario to the case of a multi-brane, six-dimensional
brane-world and discuss how multi-brane worlds may shed light on the generation
index of the SM matter content.Comment: 24 pages, 1 figure; references adde
Signals from extra dimensions decoupled from the compactification scale
Multilocalization provides a simple way of decoupling the mass scale of new
physics from the compactification scale of extra dimensions. It naturally
appears, for example, when localization of fermion zero modes is used to
explain the observed fermion spectrum, leaving low energy remnants of the
geometrical origin of the fermion mass hierarchy. We study the phenomenology of
the simplest five dimensional model with order one Yukawa couplings reproducing
the standard fermion masses and mixing angles and with a light Kaluza-Klein
quark Q_{2/3} saturating experimental limits on V_{tb} and m_Q, and then with
observable new effects at Tevatron.Comment: 18 pages, 7 figs; v2 reference and comments added to match the
published version. A discussion of the limits from precision electroweak data
is included. Conclusions are unchange
Massive Gravity on a Brane
At present no theory of a massive graviton is known that is consistent with
experiments at both long and short distances. The problem is that consistency
with long distance experiments requires the graviton mass to be very small.
Such a small graviton mass however implies an ultraviolet cutoff for the theory
at length scales far larger than the millimeter scale at which gravity has
already been measured. In this paper we attempt to construct a model which
avoids this problem. We consider a brane world setup in warped AdS spacetime
and we investigate the consequences of writing a mass term for the graviton on
a the infrared brane where the local cutoff is of order a large (galactic)
distance scale. The advantage of this setup is that the low cutoff for physics
on the infrared brane does not significantly affect the predictivity of the
theory for observers localized on the ultraviolet brane. For such observers the
predictions of this theory agree with general relativity at distances smaller
than the infrared scale but go over to those of a theory of massive gravity at
longer distances. A careful analysis of the graviton two-point function,
however, reveals the presence of a ghost in the low energy spectrum. A mode
decomposition of the higher dimensional theory reveals that the ghost
corresponds to the radion field. We also investigate the theory with a brane
localized mass for the graviton on the ultraviolet brane, and show that the
physics of this case is similar to that of a conventional four dimensional
theory with a massive graviton, but with one important difference: when the
infrared brane decouples and the would-be massive graviton gets heavier than
the regular Kaluza--Klein modes, it becomes unstable and it has a finite width
to decay off the brane into the continuum of Kaluza-Klein states.Comment: 26 pages, LaTeX. v2: extended version with an appendix added about
non Fierz-Pauli mass terms. Few typos corrected. Final version appeared in
PR
Successful Yukawa structures in Warped Extra Dimensions
For a RS model, with SM fields in the bulk and the Higgs boson on the
TeV-brane, we suggest two specific structures for the Yukawa couplings, one
based on a permutation symmetry and the other on the Universal Strength of
Yukawa couplings hypothesis (USY). In USY, all Yukawa couplings have equal
strength and the difference in the Yukawa structure lies in some complex phase.
In both scenarios, all Yukawa couplings are of the same order of magnitude.
Thus, the main features of the fermion hierarchies are explained through the RS
geometrical mechanism, and not because some Yukawa coupling is extremely small.
We find that the RS model is particularly appropriate to incorporate the
suggested Yukawa configurations. Indeed, the RS geometrical mechanism of
fermion locations along the extra dimension, combined with the two Yukawa
scenarios, reproduces all the present experimental data on fermion masses and
mixing angles. It is quite remarkable that in the USY case, only two complex
phases of definite value +-Pi/2 are sufficient to generate the known neutrino
mass differences, while at same time, permitting large leptonic mixing in
agreement with experiment.Comment: 11 page
Fermion localization on branes with generalized dynamics
In this letter we consider a specific model of braneworld with nonstandard
dynamics diffused in the literature, specifically we focus our attention on the
matter energy density, the energy of system, the Ricci scalar and the thin
brane limit. As the model is classically stable and capable of localize
gravity, as a natural extension we address the issue of fermion localization of
fermions on a thick brane constructed out from one scalar field with
nonstandard kinetic terms coupled with gravity. The contribution of the
nonstandard kinetic terms in the problem of fermion localization is analyzed.
It is found that the simplest Yukawa coupling support
the localization of fermions on the thick brane. It is shown that the zero mode
for left-handed can be localized on the thick brane depending on the values for
the coupling constant .Comment: 6 pages, 3 figure
Wave Function of the Radion in the dS and AdS Brane Worlds
We study the linearized metric perturbation corresponding to the radion for
the generalization of the five dimensional two brane setup of Randall and
Sundrum to the case when the curvature of each brane is locally constant but
non-zero. We find the wave fuction of the radion in a coordinate system where
each brane is sitting at a fixed value of the extra coordinate. We find that
the radion now has a mass, which is negative for the case of de Sitter
branes but positive for anti de Sitter branes. We also determine the couplings
of the radion to matter on the branes, and construct the four dimensional
effective theory for the radion valid at low energies. In particular we find
that in AdS space the wave function of the radion is always normalizable and
hence its effects, though small, remain finite at arbitrarily large brane
separations.Comment: Version which appears in Phys. Rev.
Dynamical Stability of Six-Dimensional Warped Brane-Worlds
We study a generalization of the Randall-Sundrum mechanism for generating the
weak/Planck hierarchy, which uses two rather than one warped extra dimension,
and which requires no negative tension branes. A 4-brane with one exponentially
large compact dimension plays the role of the Planck brane. We investigate the
dynamical stability with respect to graviton, graviphoton and radion modes. The
radion is shown to have a tachyonic instability for certain models of the
4-brane stress-energy, while it is stable in others, and massless in a special
case. If stable, its mass is in the milli-eV range, for parameters of the model
which solve the hierarchy problem. The radion is shown to couple to matter with
gravitational strength, so that it is potentially detectable by
submillimeter-range gravity experiments. The radion mass can be increased using
a bulk scalar field in the manner of Goldberger and Wise, but only to order
MeV, due to the effect of the large extra dimension. The model predicts a
natural scale of 10^{13} GeV on the 4-brane, making it a natural setting for
inflation from the ultraviolet brane.Comment: 28 pages, 7 figure
Multigravity in six dimensions: Generating bounces with flat positive tension branes
We present a generalization of the five dimensional multigravity models to
six dimensions. The key characteristic of these constructions is that that we
obtain solutions which do not have any negative tension branes while at the
same time the branes are kept flat. This is due to the fact that in six
dimensions the internal space is not trivial and its curvature allows bounce
configurations with the above feature. These constructions give for the first
time a theoretically and phenomenologically viable realization of multigravity.Comment: 27 pages, 13 figures, typos correcte
Radion Dynamics and Electroweak Physics
The dynamics of a stabilized radion in the Randall-Sundrum model (RS) with
two branes is investigated, and the effects of the radion on electroweak
precision observables are evaluated. The radius is assumed to be stabilized
using a bulk scalar field as suggested by Goldberger and Wise. First the mass
and the wavefunction of the radion is determined including the backreaction of
the bulk stabilization field on the metric, giving a typical radion mass of
order the weak scale. This is demonstrated by a perturbative computation of the
radion wavefunction. A consequence of the background configuration for the
scalar field is that after including the backreaction the Kaluza-Klein (KK)
states of the bulk scalars couple directly to the Standard Model fields on the
TeV brane. Some cosmological implications are discussed, and in particular it
is found that the shift in the radion at late times is in agreement with the
four-dimensional effective theory result. The effect of the radion on the
oblique parameters is evaluated using an effective theory approach. In the
absence of a curvature-scalar Higgs mixing operator, these corrections are
small and give a negative contribution to S. In the presence of such a mixing
operator, however, the corrections can be sizable due to the modified Higgs and
radion couplings.Comment: 42 pages, LaTeX, 14 figures; v2: minor changes and references added.
To appear in PR