Quantum decay of false vacuum states via the nucleation of bubbles may have played an important role in the early history of our Universe. For example, in multiverse models that utilize false vacuum eternal inflation, the Big Bang of our observable Universe corresponds to one of these bubble nucleation events. Further, our observable Universe may have undergone a series of symmetry-breaking firs ... More

We offer a geometric interpretation of attractor theories with singular kinetic terms as a union of multiple canonical models. We demonstrate that different domains (separated by poles) can drastically differ in their phenomenology. We illustrate this with the help of a "master model'' that leads to distinct predictions depending on which side of the pole the field evolves before examining the ... More

In this talk, we present whether the new ekpyrotic scenario can be embedded into ten-dimensional supergravity. We use that the scalar potential obtained from flux compactifications of type II supergravity with sources has a universal scaling with respect to the dilaton and the volume mode. Similar to the investigation of inflationary models, we find very strong constraints ruling out ekpyrosis fro ... More

Matrix Inflation, or M-flation in brevity, is a string theory motivated model of inflation that uses the matrix degrees of freedom of a stack of D3 branes in appropriate fluxes to realize inflation. In its minimal format, inflatons are minimally coupled to gravity. In order to match M-flation with observation, one needs a large number of D3-branes that can backreact on the background geometry. Pa ... More

While most particle physics models from string theory have been constructed in settings with some amount of supersymmetry, there has not been any experimental evidence, that it is actually realized in nature. We show that by starting from non-supersymmetric heterotic strings it is possible to construct models which have particle spectra surprisingly close to that of the Standard Model of particle ... More

Solving non-perturbative, real-time dynamics of quantum field theory is big challenge. In this presentation we shall describe how Cauchy's theorem, and a sojourn into complex field-space, allows for the solution of the real-time path integral. This is achieved by showing that the Schwinger-Keldysh calculation may be split into two pieces, which ultimately guarantees a single saddle point in the Mo ... More

The Wilsonian renormalization group (RG) requires Euclidean signature. The conformal factor of the metric then has a wrong-sign kinetic term, which has a profound effect on its RG properties. In particular around the Gaussian fixed point, it supports a Hilbert space of renormalizable interactions involving arbitrarily high powers of the gravitational fluctuations. These interactions are characteri ... More

In this talk I will describe how to use effective field theory techniques to calculate quantum gravitational corrections to different physical systems ranging from stars and black holes to inflationary models.

4-dimensional Starobinsky model, whose action has a curvature squared R^2 term, is one of the most promising inflation models. However the origin of the higher curvature term is still unknown. From the viewpoint of high energy physics, higher curvature terms should appear as a series of curvature, i.e. there must exist R^m (2<m) terms. In previous research, the authors added a R^m (2<m) term to 4- ... More

We review scenarios of baryogenesis through leptogenesis at early epochs of the universe, in string-inspired minimal extensions of the Standard Model (SM), involving heavy right-handed Majorana neutrinos. Spontaneous violation of CPT symmetry is induced by appropriate (in general, temperature-dependent) backgrounds of the Kalb-Ramond (KR) axion field, which has its origins in the (bosonic) massle ... More

We construct type I string models where supersymmetry is spontaneously broken, which have exponentially small cosmological constant and are tachyon free at 1-loop. These theories have rigid Wilson lines associated with stacked branes. Models with positive effective potentials of runaway type are also presented.

The effective field theory of cosmic inflation has been highly constrained by the swampland conditions recently. In brane inflation the Friedmann equation is modified to include an additional parameter λ called brane tension that modifies the slow-roll parameters such that the restrictive swampland conditions can be naturally evaded. We discuss superconformal α-attractor E-models that are consis ... More

String theory often predicts the incorporation of a plentitude of ultralight scalars or axion like particles stemming from the topological complexity of the extra-dimensional spacetime manifold, defining the phenomenological landscape of the string axiverse. Randomised axiverse landscapes offer an inviting approach to probing the complexities of the axion field potentials in a self-consistent but ... More

We consider string theory compactifications where the effective four-dimensional space-time, the internal space and the background fluxes are all time-dependent. For these cases we analyse the existence of four-dimensional effective field theories.

Flavor symmetry plays a crucial role in the standard model of particle physics but its origin is still unknown. A new method is presented to determine flavor symmetries within compactified string theory. This method is based on the outer automorphisms of the Narain space group of an orbifold. The resulting flavor symmetries are hence closely related to modular symmetries (i.e. T-duality). By apply ... More