38 research outputs found
String Unification at Intermediate Energies: Phenomenological Viability and Implications
Motivated by the fact that the string scale can be many orders of magnitude
lower than the Planck mass, we investigate the required modifications in the
MSSM --functions in order to achieve intermediate (GeV)
scale unification, keeping the traditional logarithmic running of the gauge
couplings. We present examples of string unified models with the required extra
matter for such a unification while we also check whether other MSSM properties
(such as radiative symmetry breaking) are still applicable.Comment: 11 pages, 2 figure included in the ps file, uses psfig.st
Towards a realistic Standard Model from D-brane configurations
Effective low energy models arising in the context of D-brane configurations
with Standard Model (SM) gauge symmetry extended by several gauged abelian
factors are discussed. The models are classified according to their hypercharge
embeddings consistent with the SM spectrum hypercharge assignment. Particular
cases are analyzed according to their perspectives and viability as low energy
effective field theory candidates. The resulting string scale is determined by
means of a two-loop renormalization group calculation. Their implications in
Yukawa couplings, neutrinos and flavor changing processes are also presented.Comment: 22 pages, 12 EPS figures, some clarifications/references adde
Modular Weights, U(1)'s and Mass Matrices
We derive the scalar mass matrices in effective supergravity models augmented
by a family symmetry. Simple relations between charges and
modular weights of the superfields are derived and used to express the matrices
with a minimum number of parameters. The model predicts a branching ratio for
the process close to the present experimental limits.Comment: LaTex file, 11 pages, 1 Figure.Typos corrected and a reference has
been added. Accepted in Phys. Lett.
Gauge Unification and Quark Masses in a Pati-Salam Model from Branes
We investigate the phase space of parameters in the Pati-Salam model derived
in the context of D-branes scenarios, requiring low energy string scale. We
find that a non-supersymmetric version complies with a string scale as low as
10 TeV, while in the supersymmetric version the string scale raises up to ~2 x
10^7 TeV. The limited energy region for RGE running demands a large tan(beta)
in order to have experimentally acceptable masses for the top and bottom
quarks.Comment: 11 pages, LaTeX, 7 figures include
Gauge coupling flux thresholds, exotic matter and the unification scale in F-SU(5) GUT
We explore the gauge coupling relations and the unification scale in F-theory
SU(5) GUT broken down to the Standard Model by an internal U(1)Y gauge flux. We
consider variants with exotic matter representations which may appear in these
constructions and investigate their role in the effective field theory model.
We make a detailed investigation on the conditions imposed on the extraneous
matter to raise the unification scale and make the color triplets heavy in
order to avoid fast proton decay. We also discuss in brief the implications on
the gaugino masses.Comment: 20 pages, 3 figures, references and extended comments on KK
thresholds effects adde
Unification, KK-thresholds and the top Yukawa coupling in F-theory GUTs
In a class of F-theory SU(5) GUTs the low energy chiral mass spectrum is
obtained from rank one fermion mass textures with a hierarchical structure
organised by U(1) symmetries embedded in the exceptional E_8 group. In these
theories chiral fields reside on matter `curves' and the tree level masses are
computed from integrals of overlapping wavefuctions of the particles at the
triple intersection points. This calculation requires knowledge of the exact
form of the wavefuctions. In this work we propose a way to obtain a reliable
estimate of the various quantities which determine the strength of the Yukawa
couplings. We use previous analysis of KK threshold effects to determine the
(ratios of) heavy mass scales of the theory which are involved in the
normalization of the wave functions. We consider similar effects from the
chiral spectrum of these models and discuss possible constraints on the
emerging matter content. In this approach, we find that the Yukawa couplings
can be determined solely from the U(1) charges of the states in the
`intersection' and the torsion which is a topological invariant quantity. We
apply the results to a viable SU(5) model with minimal spectrum which satisfies
all the constraints imposed by our analysis. We use renormalization group
analysis to estimate the top and bottom masses and find that they are in
agreement with the experimental values.Comment: 28 pages, 2 figure
Supersymmetric Monojets at the Large Hadron Collider
Supersymmetric monojets may be produced at the Large Hadron Collider by the
process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a
jet recoiling against missing transverse momentum. We discuss the feasibility
and utility of the supersymmetric monojet signal. In particular, we examine the
possible precision with which one can ascertain the neutralino_1-squark-quark
coupling via the rate for monojet events. Such a coupling contains information
on the composition of the neutralino_1 and helps bound dark matter direct
detection cross-sections and the dark matter relic density of the neutralino_1.
It also provides a check of the supersymmetric relation between gauge couplings
and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an
error that appears in all previous versions of the appendix. This error has
no effect on the results in the main body of the pape