44 research outputs found
Revisiting light stringy states in view of the 750 GeV diphoton excess
We investigate light massive string states that appear at brane
intersections. They replicate the massless spectrum in a richer fashion and may
be parametrically lighter than standard Regge excitations. We identify the
first few physical states and determine their BRST invariant vertex operators.
In the supersymmetric case we reconstruct the super-multiplet structure. We
then compute some simple interactions, such as the decay rate of a massive
scalar or vector into two massless fermions. Finally we suggest an alternative
interpretation of the 750 GeV diphoton excess at LHC in terms of a light
massive string state, a replica of the Standard Model Higgs.Comment: 29 pages, 5 eps figures. v
Quark mass hierarchies in D-brane realizations of the Standard Model
This proceeding is based on arXiv:0905.3044. We analyze the problem of the
hierarchy of masses and mixings in orientifold realizations of the Standard
Model. We present a bottom-up brane configuration that can generate such
hierarchies.Comment: Prepared for the 9th Hellenic School on Elementary Particle Physics
(CORFU2009), Corfu, Greece, 30 Aug - 20 Sep 2009. To be published in
Fortsch.Phys. 8 pages, 1 figure, LaTe
Discrete symmetries from hidden sectors
We study the presence of abelian discrete symmetries in globally consistent
orientifold compactifications based on rational conformal field theory. We
extend previous work [1] by allowing the discrete symmetries to be a linear
combination of U(1) gauge factors of the visible as well as the hidden sector.
This more general ansatz significantly increases the probability of finding a
discrete symmetry in the low energy effective action. Applied to globally
consistent MSSM-like Gepner constructions we find multiple models that allow
for matter parity or Baryon triality.Comment: 20 page
Three- and Four-point correlators of excited bosonic twist fields
We compute three- and four-point correlation functions containing excited
bosonic twist fields. Our results can be used to determine properties, such as
lifetimes and production rates, of massive string excitations localised at
D-brane intersections, which could be signatures of a low string scale even if
the usual string resonances are inaccessible to the LHC.Comment: 42 pages, no figure
Light stringy states
We carefully study the spectrum of open strings localized at the
intersections of D6-branes and identify the lowest massive 'twisted' states and
their vertex operators, paying particular attention to the signs of the
intersection angles. We argue that the masses of the lightest states scale as
M^2 ~ \theta M^2_s and can thus be parametrically smaller than the string
scale. Relying on previous analyses, we compute scattering amplitudes of
massless 'twisted' open strings and study their factorization, confirming the
presence of the light massive states as sub-dominant poles in one of the
channels.Comment: 27 pages, 1 figure (v2 Minor corrections, references added
Light stringy states and the of the muon
In this work, we evaluate the contributions to the anomalous magnetic moment
of the muon () coming from light stringy states in a D-brane
semi-realistic configuration. A scalar which couples only to the muon can have
a mass sufficiently light to provide a significant contribution to the
. This scenario can arise in intersecting D-brane models, where
such light scalars correspond to the first stringy excitations of an open
string stretched between two D-branes intersecting with a very small angle. In
this article, we show that there is a region in the space of the geometric
parameters of the internal manifold where such scalar light stringy states can
explain (part) of the observed discrepancy in the . In a low
string scale framework with , we show that an excited
Higgs with mass , living in an intersection with an
angle of order , can provide a significant contribution
of one-tenth of the discrepancy. This leads to a lower bound for
the compact dimension where the branes intersect of order
. We also study patterns in D-brane
configurations that realize our proposal, both in three and four stacks models.Comment: 26 pages, 9 figure
On mass hierarchies in orientifold vacua
We analyze the problem of the hierarchy of masses and mixings in orientifold
realizations of the Standard Model. We find bottom-up brane configurations that
can generate such hierarchies.Comment: 41 pages, 1 figure, LaTeX. (V2) A new section and references have
been adde