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 g−2g-2 of the muon

In this work, we evaluate the contributions to the anomalous magnetic moment of the muon ($(g-2)_{\mu}$) 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 $(g-2)_{\mu}$. 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 $(g-2)_{\mu}$. In a low string scale framework with $M_s\sim 10~{\rm TeV}$, we show that an excited Higgs with mass $\mathcal{O}(250~{\rm MeV})$, living in an intersection with an angle of order $\mathcal{O}(10^{-10})$, can provide a significant contribution of one-tenth of the $(g-2)_{\mu}$ discrepancy. This leads to a lower bound for the compact dimension where the branes intersect of order $\mathcal{O}(10^{-8}~{\rm GeV}^{-1})$. 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