Ashfaque,  Stable Semi-Realistic Non-Supersymmetric Heterotic String Vacua, pdf

We present a non-supersymmetric tachyon free model and discuss its relation to the supersymmetric counterpart. 

 

Atal, Spiral embedings of inflation, pdf

We present spiral embedings of the most common inflationary potentials, and show that some models that are inconsistent with data can become consistent. We show this in particular for the quadratic potential and the natural potential with subplanckian decay constant. The spiral embeding, where the radial field is stabilized at subplanckian field values, means that there are corrections to the effective potential and that there is a reduced speed of sound for the adiabatic fluctuation. Both of these effects makes theories flow in the (ns,r) potential.

 

Athanasopoulos, Free fermionic models and orbifolds, pdf

We discuss the correspondence of the orbifold and free fermion worldsheet constructions of the heterotic string, providing a detailed dictionary about how to translate models from one formalism to the other and discussing some of the more technical issues that arise.

 

Baron, M-theory origin of N=8 gauged supergravities, pdf

Supergravity theories are generally believed to describe some low-energy approximation of string theory models. There is, however, a huge landscape of 4-dimensional supergravity models whose higher-dimensional origin is not clear yet. This is already true for the most constrained scenario of maximal supergravities. In this talk we will review the current understanding of this problem with special emphasis in the uplifting of non compact supergravites and their relation with Exceptional Generalised Geometry. 

 

Damian, Type IIB vacua from G-theory, pdf

We find analytic solutions of type IIB supergravity on geometries that locally take the form Mink x M4 x C with M4 a generalised complex manifold. The solutions involve the metric, the dilaton, NSNS and RR flux potentials (oriented along the M4) parametrised by functions varying only over C. Under this assumption, the supersymmetry equations are solved using the formalism of pure spinors in terms of a finite number of holomorphic functions. Alternatively, the solutions can be viewed as vacua of maximally supersymmetric supergravity in six dimensions with a set of scalar fields varying holomorphically over C. For a class of solutions characterised by up to five holomorphic functions, we outline how the local solutions can be completed to four-dimensional flux vacua of type IIB theory. The fluxes of the global solutions are, as in F-theory, entirely codified in the geometry of an auxiliary K3 fibration over CP1.

 

Dutta, A relation between inflation and non-thermal history of the Universe, pdf

We consider cosmological scenarios in which density perturbations are generated by the quantum fluctuations of the inflaton field at early times; the late time dynamics involves a modulus which first dominates the energy density of the universe and then decays to reheat the visible sector. By examining the evolution of energy density of the universe from the time of horizon exit of a pivot mode to the present day, and the fact that a modulus field decays via Planck suppressed interactions, we arrive at a relation which relates the mass of the modulus, inflationary observables/parameters and broad characteristics of the post inflationary reheating phase. When viewed together with generic expectations regarding reheating and the initial field displacement of the modulus after inflation, the relation gives a strong constraint on inflationary models given a modulus mass or vice versa.

 

Krippendorf, Phenomenology of U(1) charges in F-theory,

I discuss how U(1) symmetries can be used in F-theory GUT model building to avoid rapid proton decay and can generate an interesting flavour structure. The focus is on SU(5) GUT constructions with hypercharge flux breaking that do not suffer from any gauge anomalies and lead to the exact MSSM matter spectrum at low-energies.

 

Kuwakino, Heterotic asymmetric orbifolds, pdf

Model building by heterotic asymmetric orbifold compactification is considered. Narain lattices which can be starting points for model building and gauge symmetry breaking patterns are analysed. Three-generation models we have obtained will be shown.

 

Lüst, Moduli Spaces of AdS Vacua in d=7 Supergravity, pdf

We discuss AdS vacua of N=2 gauged supergravity in seven dimensions and classify the possible gauge groups which lead to maximally supersymmetric AdS vacua. We show that the moduli spaces of these backgrounds can consist only of isolated points. We finally compare this result to the conformal manifold of the corresponding dual SCFT in six dimensions and show that the two spaces agree.

 

Mavroudi, Phenomenology of non-supersymmetric string models, pdf

There exists a class of tachyon-free four-dimensional string models realized through coordinate-dependent compactifications. It is possible to construct models in this class whose low-lying states resemble the Standard Model (or even potential unified extensions thereof)  all without any light superpartners, and without supersymmetry at any energy scale. The existence of such models thus opens the door to general studies of non-supersymmetric string phenomenology. On the phenomenological aspect, I discuss their construction techniques, their particle and charge assignments, their natural energy scales, and the magnitudes of their associated Yukawa couplings and scalar masses. Finally I show how these models exhibit an exponentially suppressed one-loop cosmological constant. 

 

Mehta, Orbifolds as free fermionic models, pdf

We discuss the correspondence of orbifold and free fermion worldsheet constructions of the heterotic string. We contrast the two formalisms and detail scenarios in which each come to the fore, discussing both symmetric and asymmetric cases.

 

Pedro, Multifield dynamics in Higgs-otic inflation, 

In Higgs-otic inflation a complex neutral scalar combination of the MSSM Higgs fields plays the role of inflaton in a chaotic fashion. The structure of the model implies it is inherently 2 field. In this talk I will present the observable signatures of the model, highlighting the effects of multifield dynamics and comparing it with the single field adiabatic projection employed in an earlier analysis of the model.

Pugh, Higher Derivative Terms in M-Theory Reductions, pdf

M-theory, accessed via eleven-dimensional supergravity, admits solutions with eight-dimensional compact internal spaces, exhibiting fluxes and warping. These solutions require higher derivative terms in the 11d action and field equations to be properly handled, for global consistency. We will examine the induced corrections to the 11d vacua and then derive the effective theories corresponding to the reduction on these spaces. This will allow us to analyze the corrections to mass terms and kinetic terms in the 3d effective theories.

 

Scalisi, Cosmological Attractors from alpha-Scale Supergravity, pdf

The Planck value of the spectral index can be interpreted as n_s=1-2/N in terms of the number of e-foldings N. An appealing explanation for this phenomenological observation is provided by $\a$-attractors: the inflationary predictions of these supergravity models are fully determined by the curvature of the Kahler manifold. We provide a novel formulation of $\a$-attractors which only involves a single chiral superfield. Our construction involves a natural deformation of no-scale models, and employs these to construct a De Sitter plateau with an exponential fall-off. Finally, we show how analogous structures with a flat Kahler geometry arise as a singular limit of such $\a$-scale models.

 

Shukla, Towards dimensional oxidation of four-dimensional non-geometric type IIB action, pdf

It is quite remarkable that the four dimensional type II effective potentials could be studied via merely knowing the forms of Kaehler and super-potentials (and without having a full understanding of their ten-dimensional origin). In the context of type IIB superstring compactification on an orientifold of $T^6/(Z2xZ2)$, I will discuss about a proposal of dimensional oxidation of the 4D non-geometric scalar potential into ten dimensions. In the initial step of dimensional oxidation, I will consider the compactification background with standard (H3, F3)-fluxes and non-geometric Q-fluxes only. In a second step, the inclusion of P-flux (which is S-dual to Q-flux) will be considered to make the whole picture more S-duality symmetric. In a final step, we also include involutively-odd B2/C2-axions with a less simple toroidal orientifold which also allows for the presence of geometric flux (omega) and non-geometric R-flux in type IIB framework. In the process of oxidation, we invoke various new flux-orbits which are generalized at each of the three steps leading to modular completed generalized flux-orbits, and the same are useful for writing a conjectural form of the 10D non-geometric action.

 

Sonmez, The Landscape of the Free Fermionic String Vacua, pdf

The existence of discrete properties in the landscape of free fermionic heterotic-string vacua were discovered via their classification by SO(10) GUT models and its subgroups such as the Pati-Salam, Flipped SU(5) and SU(4) x SU(2) x U(1) models. The classification is carried out by fixing a set of basis vectors and varying the GGSO projection coefficients entering the one-loop partition function. The analysis of the models is facilitated by deriving algebraic expressions for the GSO projections that enable a computerised analysis of the entire string spectrum and the scanning of large spaces of vacua. The analysis reveals discrete symmetries like the spinor-vector duality observed at the SO(10) level and the existence of exophobic Pati-Salam vacua. Contrary to the Pati-Salam case the classification shows that there are no exophobic Flipped SU(5) vacua with an odd number of generations. It is observed that the SU(4) x SU(2) x U(1) models are substantially more constrained.I will present a short survey of multi-fiberation in Complete Intersection Calabi-Yau threefold, its construction and numerical statistic.

 

Sun, What can heterotic DFT give for string phenomenology?, pdf

We will introduce the non-geometric side of heterotic DFT, and based on this we complete the gauge flux chain with the non-geometric gauge flux explicit given. Hopefully this can bring new element for string phenomenology to play with. 

 

Welling, Multiple field inflation with additional heavy fields, pdf

In this talk we give a pedagogical introduction to multiple field inflation with additional heavy fields.

 

Wieck, Backreaction of heavy fields in string-effective inflation models, pdf

We study the compatibility of large-field inflation and Kähler moduli stabilization in N=1 supergravity models. By calculating the backreaction of a single volume modulus on the inflaton potential we show that both inflation and moduli stabilization face a series of obstacles. In chaotic inflation, the initial conditions must be chosen very carefully and the scale of supersymmetry breaking must be very large for popular models to remain viable. In no-scale embeddings of the Starobinsky model, inflation is either severely constrained or impossible once all moduli are stabilized consistently.

 

Zoccarato, Yukawa Hierarchies at the point of E8 in F-theory, pdf

In this talk I will present the analysis of Yukawa couplings in a local SU(5) Grand Unified Theory close to a point of E8 enhancement. In this setting all masses for the fermions are generated and only one generation acquires a mass. Taking into account non-perturbative effects the other two families acquire a mass which is hierarchically smaller compared to the mass of the first generation. I will show how, while many different pattern for the embedding of the MSSM fields inside E8 are available, only a limited number of these allow for suitable hierarchies in the fermion masses. I will show how in one of these models it is possible to achieve masses compatible with the empirical data, and finally discuss the computation of the CKM matrix in this particular model.