86305487
Origin of family symmetries
Discrete (family) symmetries might play an important role in models of elementary particle physics. We discuss the origin of such symmetries in the framework of consistent ultraviolet completions of the standard model in field and string theory. The symmetries can arise due to special geometrical properties of extra compact dimensions and the localization of fields in this geometrical landscape. We also comment on anomaly constraints for discrete symmetries.
119225168
An involuted orbifold MSSM
A compactification of the E8 × E8 heterotic string on a ℤ2 × ℤ2 orbifold equipped with an additional freely acting involution is presented. This model reproduces the exact chiral MSSM spectrum with matter parity and a non-trivial Yukawa structure. The key ingredient is a freely acting Wilson line associated to the involution, breaking SU(5) to SU(3) × SU(2) × U(1)Y. This work is based on a talk given at the “9th Hellenic School and Workshop on Elementary Particle Physics and Gravity” and reviews the results of a collaboration with M. Blaszczyk, S. Groot Nibbelink, M. Ratz, F. Ruhle and M. Trapletti.
119283726
Schoen manifold with line bundles as resolved magnetized orbifolds
A bstractWe give an alternative description of the Schoen manifold as the blow-up of a $ {{\mathbb{Z}}_2}\times {{\mathbb{Z}}_2} $ orbifold in which one $ {{\mathbb{Z}}_2} $ factor acts as a roto-translation. Since for this orbifold the fixed tori are only identified in pairs but not orbifolded, four-dimensional chirality can never be obtained in heterotic string compactifications using standard techniques alone. However, chirality is recovered when its tori become magnetized. To exemplify this, we construct an E8 × E8′ heterotic SU(5) GUT on the Schoen manifold with Abelian gauge fluxes, which becomes an MSSM with three generations after an appropriate Wilson line is associated to its freely acting involution. We reproduce this model as a standard heterotic orbifold CFT of the (partially) blown down Schoen manifold with a magnetic flux. Finally, in analogy to a proposal for non-perturbative heterotic models by Aldazabal et al. we suggest modifications to the heterotic orbifold spectrum formulae in the presence of magnetized tori.
126022661
Discrete symmetries in semi-realistic orientifold compactiﬁcations
This proceeding is based on arXiv:1211.1017 [hep-th] where we study the presence of discrete gauge symmetries in D-brane semi-realistic quivers. After establishing the constraints on the transformation behaviour of the chiral matter for the presence of a discrete gauge symmetry we perform a systematic search for discrete gauge symmetries within semi-realistic local D-brane realizations, based on four D-brane stacks. This search reveals that Proton hexality, a discrete symmetry which ensures the absence of R-parity violating terms as well as the absence of dangerous dimension 5 proton decay operators, is only rarely realized. Furthermore, we do not find any semi-realistic local D-brane configurations exhibiting a family dependent discrete gauge symmetry.
119190647
No-go theorems for R symmetries in four-dimensional GUTs
We prove that it is impossible to construct a grand unified model, based on a simple gauge group, in four dimensions that leads to the exact MSSM, nor to a singlet extension, and possesses an unbroken R symmetry. This implies that no MSSM model with either a ZM⩾3R or U(1)R symmetry can be completed by a four-dimensional GUT in the ultraviolet. However, our no-go theorem does not apply to GUT models with extra dimensions. We also show that it is impossible to construct a 4D GUT that leads to the MSSM plus an additional anomaly-free symmetry that forbids the μ term.
1249780
(Non-)Abelian discrete anomalies
Abstract We derive anomaly constraints for Abelian and non-Abelian discrete symmetries using the path integral approach. We survey anomalies of discrete symmetries in heterotic orbifolds and find a new relation between such anomalies and the so-called ‘anomalous’ U(1).
119592670
Trans-Planckian Issue in the Milne Universe
The ``trans-Planckian'' challenge in cosmology appears when we trace the present physical wavelengths of fluctuations backwards in time. They become smaller and smaller until crossing the Planck scale where conventional QFT is challenged, so that unknown ultraviolet physics may be traced in the observable cosmological fluctuations. Usually this issue is addressed in the inflationary context, but trans-Planckian reasoning is much broader. We examine this logic in a simple example of scalar quantum field theory in the expanding and contracting Milne universes, where wavelengths of the eigenmodes are red- or blue-shifted. Trans-Planckian modifications of QFT should result in a UV-dependent VeV of the energy momentum tensor of a scalar field in the Milne universe. On the other hand, the Milne universe is another coordinate systems of flat Minkowski space-time, and the covariant energy momentum tensor should be the same (but vacuum-dependent) in different coordinates of flat space time. We explicitly demonstrate that in conventional QFT the energy momentum tensor, choosing the adiabatic vacuum, is identical to zero in Minkowski coordinates, and remains zero in the contracting Milne universe (due to non-trivial cancellations of contributions from particles which appear in the accelerating frame and from vacuum polarization there). In contrast to this, the trans-Planckian modification of the energy momentum tensor is not motivated. We provide a similar argument for the expanding Milne universe, where the energy momentum tensor in the conformal vacuum is non-zero. Similar arguments are applicable for other cosmological models where the curvature is much lower than Planckian which leads to conflicts with trans-Planckian considerations.
117445431
Gravity waves from the non-renormalizable Electroweak Vacua phase transition
It is currently believed that the Standard Model is an effective low energy theory which in principle may contain higher dimensional non-renormalizable operators. These operators may modify the standard model Higgs potential in many ways, one of which being the appearance of a second vacuum. For a wide range of parameters, this new vacuum becomes the true vacuum. It is then assumed that our universe is currently sitting in the false vacuum. Thus the usual second-order electroweak phase transition at early times will be followed by a second, first-order phase transition. In cosmology, a first-order phase transition is associated with the production of gravity waves. In this paper we present an analysis of the production of gravitational waves during such a second electroweak phase transition. We find that, for one certain range of parameters, the stochastic background of gravitational waves generated by bubble nucleation and collision have an amplitude which is estimated to be of order $\Omega_{GW}h^2\sim10^{-11}$ at $f=3\times 10^{-4}$Hz, which is within reach of the planned sensitivity of LISA. For another range of parameters, we find that the amplitude is estimated o be of order $\Omega_{GW}h^2\sim10^{-25}$ around $f=10^3$Hz, which is within reach of LIGO. Hence, it is possible to detect gravity waves from such a phase transition at two different detectors, with completely different amplitude and frequency ranges.
15531733
Roulette inflation with Kahler moduli and their axions
We study 2-field inflation models based on the 'large-volume' flux compactification of type IIB string theory. The role of the inflaton is played by a Kaehler modulus {tau} corresponding to a 4-cycle volume and its axionic partner {theta}. The freedom associated with the choice of Calabi-Yau manifold and the nonperturbative effects defining the potential V({tau},{theta}) and kinetic parameters of the moduli brings an unavoidable statistical element to theory prior probabilities within the low-energy landscape. The further randomness of ({tau},{theta}) initial conditions allows for a large ensemble of trajectories. Features in the ensemble of histories include 'roulette trajectories', with long-lasting inflations in the direction of the rolling axion, enhanced in the number of e-foldings over those restricted to lie in the {tau}-trough. Asymptotic flatness of the potential makes possible an eternal stochastic self-reproducing inflation. A wide variety of potentials and inflaton trajectories agree with the cosmic microwave background and large scale structure data. In particular, the observed scalar tilt with weak or no running can be achieved in spite of a nearly critical de Sitter deceleration parameter and consequently a low gravity wave power relative to the scalar curvature power.