22 research outputs found

### Limits on Kaluza-Klein Models from COBE Results

The large-angular-scale anisotropy of the cosmic microwave background
radiation in multidimensional cosmological models (Kaluza-Klein models) is
studied. Limits on parameters of the models imposed by the experimental data
are obtained. It is shown that in principle there is a room for Kaluza-Klein
models as possible candidates for the description of the Early Universe.
However, the obtained limits are very restrictive and none of the concrete
models, analyzed in the article, satisfy them.Comment: 9 pages, Latex, one figure available on request at the following
adress: [email protected]

### Model building by coset space dimensional reduction in ten-dimensions with direct product gauge symmetry

We investigate ten-dimensional gauge theories whose extra six-dimensional
space is a compact coset space, $S/R$, and gauge group is a direct product of
two Lie groups. We list up candidates of the gauge group and embeddings of $R$
into them. After dimensional reduction of the coset space,we find fermion and
scalar representations of $G_{\mathrm{GUT}} \times U(1)$ with
$G_{\mathrm{GUT}}=SU(5), SO(10)$ and $E_6$ which accomodate all of the standard
model particles. We also discuss possibilities to generate distinct Yukawa
couplings among the generations using representations with a different
dimension for $G_{\mathrm{GUT}}=SO(10)$ and $E_6$ models.Comment: 14 pages; added local report number, added refferenc

### Decoupling of Heavy Kaluza-Klein Modes In Models With Five-Dimensional Scalar Fields

We investigate the decoupling of heavy Kaluza-Klein modes in $\phi^{4}$
theory and scalar QED with space-time topology $\mathbb{R}^{3,1} \times S^{1}$.
We calculate the effective action due to integrating out heavy KK modes. We
construct generalized RGE's for the couplings with respect to the
compactification scale $M$. With the solutions to the RGE's we find the
$M$-scale dependence of the effective theory due to higher dimensional quantum
effects. We find that the heavy modes decouple in $\phi^{4}$ theory, but do not
decouple in scalar QED. This is due to the zero mode of the 5-th component
$A_{5}$ of the 5-d gauge field. Because $A_{5}$ is a scalar under 4-d Lorentz
transformations, there is no gauge symmetry protecting it from getting mass and
$A_{5}^{4}$ interaction terms after loop corrections. In light of these
unpleasant features, we explore $S^{1}/\mathbb{Z}_{2}$ compactifications, which
eliminate $A_{5}$, allowing for the heavy modes to decouple at low energies. We
also explore the possibility of decoupling by including higher dimensional
operators. It is found that this is possible, but a high degree of fine tuning
is required.Comment: 9 pages, no figures; sign error on equations 20, 36, 37; Added
additional reference

### Scalar Kaluza-Klein modes in a multiply warped braneworld

The Kaluza-Klein (KK) modes of a massive scalar field on a 3-brane embedded
in six dimensional multiply warped spacetime are determined. Due to the
presence of warping along both the extra dimensions the KK mass spectrum splits
into two closely spaced branches which is a distinct feature of this model
compared to the five dimensional Randall-Sundrum model. This new cluster of the
KK mode spectrum is expected to have interesting phenomenological implications
for the upcoming collider experiments. Such a scenario may also be extended for
even larger number of orbifolded extra dimensions.Comment: 10 pages, Revte

### Compactification, Vacuum Energy and Quintessence

We study the possibility that the vacuum energy density of scalar and
internal-space gauge fields arising from the process of dimensional reduction
of higher dimensional gravity theories plays the role of quintessence. We show
that, for the multidimensional Einstein-Yang-Mills system compactified on a $R
\times S^3 \times S^d$ topology, there are classically stable solutions such
that the observed accelerated expansion of the Universe at present can be
accounted for without upsetting structure formation scenarios or violating
observational bounds on the vacuum energy density.Comment: 15 pages, Latex, Third Award in 1999 Essay Competition of the Gravity
Research Foundatio

### Is the String Coupling Constant invariant under T-duality?

It is well known that under T-duality the sigma model dilaton (which is
normally thought to be related to the string coupling constant through the
simple formula $\kappa = exp$), undergoes an additive shift. On the
other hand, Kugo and Zwiebach, using a simplified form of string field theory,
claim that the string coupling constant does not change under the T-duality.
Obviously, what seems to happen is that two different coupling constants,
associated to different dilatons, are used. In this contribution we shall try
to clarify this, and related issues.Comment: LaTeX, 13 pag. Contributions to Santa Margherita and S. Petersburg
meeting

### Matter-gravity interaction in a multiply warped braneworld,

The role of a bulk graviton in predicting the signature of extra dimensions
through collider-based experiments is explored in the context of a multiply
warped spacetime. In particular it is shown that in a doubly warped braneworld
model, the presence of the sixth dimension, results in enhanced concentration
of graviton Kaluza Klein (KK) modes compared to that obtained in the usual
5-dimensional Randall-Sundrum model. Also, the couplings of these massive
graviton KK modes with the matter fields on the visible brane turn out to be
appreciably larger than that in the corresponding 5- dimensional model. The
significance of these results are discussed in the context of KK graviton
search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table

### Inflation in Multidimensional Quantum Cosmology

We extend to multidimensional cosmology Vilenkin's prescription of tunnelling
from nothing for the quantum origin of the observable Universe. Our model
consists of a $D+4$-dimensional spacetime of topology ${\cal R}\times {\cal
S}^3 \times{\cal S}^D$, with a scalar field (``chaotic inflaton'') for the
matter component. Einstein gravity and Casimir compactification are assumed.
The resulting minisuperspace is 3--dimensional. Patchwise we find an
approximate analytic solution of the Wheeler--DeWitt equation through which we
discuss the tunnelling picture and the probability of nucleation of the
classical Universe with compactifying extra dimensions. Our conclusion is that
the most likely initial conditions, although they do not lead to the
compactification of the internal space, still yield (power-law) inflation for
the outer space. The scenario is physically acceptable because the inner space
growth is limited to $\sim 10^{11}$ in 100 e-foldings of inflation, starting
from the Planck scale.Comment: RevTeX, 30 pages, 4 figures available via fax on request to
[email protected], submitted to Phys. Rev.

### Scalar kinks and fermion localisation in warped spacetimes

Scalar kinks propagating along the bulk in warped spacetimes provide a thick
brane realisation of the braneworld. We consider here, a class of such exact
solutions of the full Einstein-scalar system with a sine-Gordon potential and a
negative cosmological constant. In the background of the kink and the
corresponding warped geometry, we discuss the issue of localisation of spin
half fermions (with emphasis on massive ones) on the brane in the presence of
different types of kink-fermion Yukawa couplings. We analyse the possibility of
quasi-bound states for large values of the Yukawa coupling parameter $\gamma_F$
(with $\nu$, the warp factor parameter kept fixed) using appropriate, recently
developed, approximation methods. In particular, the spectrum of the low--lying
states and their lifetimes are obtained, with the latter being exponentially
enhanced for large $\nu \gamma_F$. Our results indicate quantitatively, within
this model, that it is possible to tune the nature of warping and the strength
and form of the Yukawa interaction to obtain trapped massive fermion states on
the brane, which, however, do have a finite (but very small) probability of
escaping into the bulk.Comment: 22 pages, 4 figures, RevTex

### Finite SU(N)^k Unification

We consider N=1 supersymmetric gauge theories based on the group SU(N)_1 x
SU(N)_2 x ... x SU(N)_k with matter content (N,N*,1,...,1) + (1,N,N*,...,1) +
>... + (N*,1,1,...,N) as candidates for the unification symmetry of all
particles. In particular we examine to which extent such theories can become
finite and we find that a necessary condition is that there should be exactly
three families. We discuss further some phenomenological issues related to the
cases (N,k) = (3,3), (3,4), and (4,3), in an attempt to choose those theories
that can become also realistic. Thus we are naturally led to consider the
SU(3)^3 model which we first promote to an all-loop finite theory and then we
study its additional predictions concerning the top quark mass, Higgs mass and
supersymmetric spectrum.Comment: 15 page