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

Anomalies, Anomalous U(1)'s and generalized Chern-Simons terms

A detailed analysis of anomalous U(1)'s and their effective couplings is performed both in field theory and string theory. It is motivated by the possible relevance of such couplings in particle physics, as well as a potential signal distinguishing string theory from other UV options. The most general anomaly related effective action is analyzed and parameterized. It contains Stuckelberg, axionic and Chern-Simons-like couplings. It is shown that such couplings are generically non-trivial in orientifold string vacua and are not in general fixed by anomalies. A similar analysis in quantum field theories provides similar couplings. The trilinear gauge boson couplings are also calculated and their phenomenological relevance is advocated. We do not find qualitative differences between string and field theory in this sector.Comment: 52 pages, 2 eps figures, LaTeX, feynmf & youngtab packages (v2 - Minor corrections, references added

Minimal Anomalous U(1)' Extension of the MSSM

We study an extension of the MSSM by an anomalous abelian vector multiplet and a St\"uckelberg multiplet. The anomalies are cancelled by the Green-Schwarz mechanism and the addition of Chern-Simons terms. The advantage of this choice over the standard one is that it allows for arbitrary values of the quantum numbers of the extra U(1). As a first step towards the study of hadron annihilations producing four leptons in the final state (a clean signal which might be studied at LHC) we then compute the decays Z'\to Z_0 \g and $Z'\to Z_0 Z_0$. We find that the largest values of the decay rate is $\sim 10^{-4}$ GeV, while the expected number of events per year at LHC is at most of the order of 10.Comment: 45 pages, 8 eps figures, feynmf. Phenomenological section expanded. 2 plots and references adde

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

Reheating and Leptogenesis after Vector inflation

We study the reheating and leptogenesis in the case of a vector inflaton. We concentrate on particle production during the phase of oscillating background, especially gravitational production induced by the presence of non-minimal coupling imposed by an isotropic and homogeneous Universe. Including processes involving the exchange of graviton, we then extend our study to decay into fermions via direct or anomalous couplings. The necessity of non-minimal gravitational coupling and the gauge nature of couplings to fermions implies a much richer phenomenology than for a scalar inflaton.Comment: 27 pages, 4 figures, 15 tikzpicture Feynman diagrams, 2 tables. v2: minor corrections and new discussions about ghost instablity, Gauss-Bonnet coupling, kinetic mixing and couplings with off-shell RHN include

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