Global Embedding of Fibre Inflation Models

We present concrete embeddings of fibre inflation models in globally consistent type IIB Calabi-Yau orientifolds with closed string moduli stabilisation. After performing a systematic search through the existing list of toric Calabi-Yau manifolds, we find several examples that reproduce the minimal setup to embed fibre inflation models. This involves Calabi-Yau manifolds with $h^{1,1}= 3$ which are K3 fibrations over a $\mathbb{P}^1$ base with an additional shrinkable rigid divisor. We then provide different consistent choices of the underlying brane set-up which generate a non-perturbative superpotential suitable for moduli stabilisation and string loop corrections with the correct form to drive inflation. For each Calabi-Yau orientifold setting, we also compute the effect of higher derivative contributions and study their influence on the inflationary dynamics.Comment: 27 pages + appendix, 2 figures; references adde

Affleck-Dine Baryogenesis in Type IIB String Models

We present a viable string embedding of Affleck-Dine baryogenesis in type IIB sequestered models where the late-time decay of the lightest modulus reheats the universe to relatively low temperatures. We show that if inflation is driven by a blow-up Kaehler modulus, the Affleck-Dine field can become tachyonic during inflation if the Kaehler metric for matter fields has an appropriate inflaton-dependent contribution. We find that the Affleck-Dine mechanism can generate the observed baryon asymmetry for natural values of the underlying parameters which lead also to successful inflation and low-energy gaugino masses in a split supersymmetry scenario. The reheating temperature from the lightest modulus decay is high enough to allow thermal Higgsino-like dark matter.Comment: 24 pages, 1 figur

Hidden Sectors in String Theory: Kinetic Mixings, Fifth Forces and Quintessence

Light moduli fields in string compactifications can have interesting implications for particle physics and cosmology. Fifth force bounds impose stringent constraints on the interactions of such moduli with the visible sector. To be consistent with the bounds, they need to be part of hidden sectors which interact with the Standard Model with weaker-than-Planck suppressed interactions. We consider scenarios in which the visible sector degrees of freedom are localised in the compactification and light moduli arise as closed string degrees of freedom associated with hidden sectors which are geometrically separated (in the extra-dimensions) from the Standard Model. Kinetic mixings lead to interactions between the moduli and the visible sector - we compute these using Kaehler potentials of string/M-theory compactifications. We argue that in general these interactions provide a lower bound on the strength of the interactions between the moduli and the visible sector. The interactions scale with inverse powers of the volume of the compactification, thus fifth force bounds can be translated to lower bounds on the volume of the extra-dimensions. We find that compactification volumes have to be large to evade the bounds. This imposes interesting constraints on quintessence model building in string theory. Our results for the strength of the interactions can also be used to quantify the fine-tuning necessary for the stability of the potential of a light modulus against quantum corrections involving visible sector loops

Oscillons from String Moduli

A generic feature of string compactifications is the presence of many scalar fields, called moduli. Moduli are usually displaced from their post-inflationary minimum during inflation. Their relaxation to the minimum could lead to the production of oscillons: localised, long-lived, non-linear excitations of the scalar fields. Here we discuss under which conditions oscillons can be produced in string cosmology and illustrate their production and potential phenomenology with two explicit examples: the case of an initially displaced volume modulus in the KKLT scenario and the case of a displaced blow-up Kaehler modulus in the Large Volume Scenario (LVS). One, in principle, observable consequence of oscillon dynamics is the production of gravitational waves which, contrary to those produced from preheating after high scale inflation, could have lower frequencies, closer to the currently observable range. We also show that, for the considered parameter ranges, oscillating fibre and volume moduli do not develop any significant non-perturbative dynamics. Furthermore, we find that the vacua in the LVS and the KKLT scenario are stable against local overshootings of the field into the decompatification region, which provides an additional check on the longevity of these metastable configurations.Comment: 32 pages + appendix, 23 figures, for videos of the simulations see https://particlesandcosmology.unibas.ch/downloads/oscillons-from-string-moduli-movies.htm

Emerging chromo-natural inflation

The shift-symmetric coupling of a pseudo-scalar particle driving inflation to gauge fields provides a unique way of probing cosmic inflation. We show for an SU(2) gauge group how a classical isotropic background gauge field develops from the standard quantum mechanical vacuum in the far past. Over the course of inflation, the theory dynamically evolves from an approximately abelian regime into an inherently non-abelian regime, with distinct predictions for the scalar and tensor power spectra. The latter regime closely resembles a setup known as chromo-natural inflation, although our main focus here is on a new part of the parameter space which has received little attention so far. For single-field slow roll inflation models, large scales may exit the horizon in the abelian regime, ensuring agreement with the observations of the anisotropies in the cosmic microwave background, whereas smaller scales experience the non-abelian effects. This results in a strong enhancement of the stochastic gravitational wave background at small scales, e.g. at frequencies accessible with ground-based interferometers. For the scalar power spectrum, a similar enhancement arises due to non-linear contributions.Comment: 53 pages, 6 appendixe

Sequestered de Sitter String Scenarios: Soft-terms

We analyse soft supersymmetry breaking in type IIB de Sitter string vacua after moduli stabilisation, focussing on models in which the Standard Model is sequestered from the supersymmetry breaking sources and the spectrum of soft-terms is hierarchically smaller than the gravitino mass $m_{3/2}$. Due to this feature, these models are compatible with gauge coupling unification and TeV scale supersymmetry with no cosmological moduli problem. We determine the influence on soft-terms of concrete realisations of de Sitter vacua constructed from supersymmetric effective actions. One of these scenarios provides the first study of soft-terms for consistent string models embedded in a compact Calabi-Yau manifold with all moduli stabilised. Depending on the moduli dependence of the Kaehler metric for matter fields and on the mechanism responsible to obtain a de Sitter vacuum, we find two scenarios for phenomenology: (i) a split-supersymmetry scenario where gaugino masses are suppressed with respect to scalar masses: $M_{1/2} \sim m_{3/2} \epsilon \ll m_0 \sim m_{3/2} \sqrt{\epsilon} \ll m_{3/2}$ for $\epsilon \sim m_{3/2}/M_P \ll 1$; (ii) a typical MSSM scenario where all soft-terms are of the same order: $M_{1/2} \sim m_0 \sim m_{3/2} \epsilon \ll m_{3/2}$. Background fluxes determine the numerical coefficients of the soft-terms allowing for small variations of parameters as is necessary to confront data and to interpolate between different scenarios. We comment on different stringy origins of the mu-term and potential sources of desequestering.Comment: 27 pages + appendices, 2 figure

T-duality and generalized complex geometry

Since a massless state with spin two was found in the spectrum of closed strings, the String theory has become the most promising field theory in trying to unify all the fundamental interactions in a unique framework. The introduction of fermionic matter in the String Theory brings to consider the supersymmetric extension of this, also called Superstrings Theory. These have critical dimension d = 10. The discrepancy with phenomenology, which provides only four dimensions, is filled by one of the most interesting theoretical aspects of Superstring Theory, that is the compactification of the 6 extra dimensions. The most used way to compactify the extra dimensions is called Kaluza-Klein reduction. It consists in taking the 6 extra dimensions as compact ones and ``small''. By assuming that the typical lenght of the compactified dimensions is of order 1/M_P - where M_P \sim 10^{19} Gev is the Planck mass - by Kaluza-Klein reduction a tower of states is obtained, each of which has mass proportional to n/R. At low energies, the only observable states are the massless ones. These are the vacua of the theory, and are intimately connected to the geometry of the 6-manifold on which the theory is compactified, also called the internal space K. The present work concerns the study of different aspects of the geometry of the internal space. Since the matter content of the theory is strictly related to the geometry of the internal space, phenomenology puts strong constraints on the geometry of K. The most accredited phenomenological models are currently those which provide for a N = 1 supersymmetric extension of the Standard model. The examples studied in the present work always assume that the compactification is done with the constraint of preserving N = 1 supersymmetry in the effective 4-dimensional theory. The vacua states of the Superstrings Theory are described by a tern of objects, namely (g, H, \phi), where g is the Riemannian metric, H is a three-form also called the Neveu-Schwarz flux, while \phi is the dilaton. Compactifications with vanishing H-flux have been intensively studied until the first half of the '90s, and they brought to the study of Calabi-Yau manifolds. In the present work we will deal only with non-vanishing H-fluxes. For non-vanishing H-flux the internal space geometry is not more \Kahler: it is called generalized \Kahler. The first part of the present work is devoted to the study of G-structures, which allow us to describe such a kind of manifolds. In particular we will see that the generalized \Kahler structures are SU(3) structures, and how they can be described also in terms of spinors on a manifold. T-duality is a non-local symmetry of the String theory. In the case of compactifications with H flux, the T-duality consists of a map T which associate to a background (g, H, \phi) its dual background (g', H', \phi'). At the level of local supergravity backgrounds, there exists a standard way to find the dual background, which is given by the Buscher rules. These consist in introducing a gauge field by gauging the non-linear sigma model defined by (g, H, \phi). The dual background can be simply obtained by integrating the gauge field out. One of the aspects of the present work is to understand under which conditions a dual background can be defined in a global manner. C. Hull has furnished general arguments to understand if the non-linear sigma model associated to a global background can be gauged in a way which defines a global dual background. It's in this context that the double field theory was born. In the present work we will explicitly study the non-physical example of the three-torus T^3. Even if this example can't be used as an actual background (its dimension is 3!) it is very useful since it allows us to highlight the mathematical details of the question. Moreover, even if a global treatment is possible in this case, we will see explicitly that the results locally agree with those given by Buscher rules. In particular we will explicitly show that the three-torus represents the simplest example in which an ungaugeable isometry can actually be gauged by using the double space technique. In particular, as it was formalized by V. Mathai, J. Evslin and P. Bouwknegt the topology of the background can change after T-duality. We will explicitly see this phenomenon in the T^3 example. The main point of the present work is however the systematic study of the Generalized Complex Geometry. It turns out to be the natural framework to describe generalized \Kahler structures. Since it provides a doubling of the degrees of freedom due to the fact that tangent space and cotangent spaces are merged togheter, it can be used to describe the doubled space in a natural way. In particular the T-duality map takes a very simple form when written in terms of generalized structures. It will be shown that Generalized Complex Geometry provides the right way to describe type II supergravity backgrounds, and in this context we will consider two explicit examples which are SU(3) structures. In particular we will study the form of the T-duality map written in terms of pure spinors for these examples, and we will see explicitly that the local form of such a map is equivalent to that prescribed by Buscher rules. Doubtless the most interesting point is to understand if such local dual supergravity backgrounds can be extended to global Superstring backgrounds. We will see explicitly that the examples considered are T-folds according to the definition given by Hull and we will study the mathematical details which descend from it. In particular we will concentrate on the generalized geometry consequences for T-folds

Sequestered String Models: Supersymmetry Breaking and Cosmological Applications

In the present thesis I focused on the study of the phenomenology arising from a class of string models called sequestered compactifications, which were born with the aim of getting low-energy SUSY from strings. This is not an easy task if combined with cosmological constraints, since the mechanism of moduli stabilization fixes both the scale of supersymmetric particles and the scale of moduli, which tend to be of the same order. However, if on the one hand supersymmetric particles with TeV mass are desired in order to address the electroweak hierarchy problem, on the other hand the cosmological moduli problem requires the moduli to be heavier than 100 TeV. The specific setup of sequestered compactifications makes this hierarchy achievable, at least in principle: as in these models the visible sector is located on a stack of D3-branes at singularities, a physical separation between the visible degrees of freedom and the SUSY-breaking sources takes place. Such decoupling translates into a hierarchy between the scale of SUSY-breaking and the spectrum of supersymmetric particles. Interestingly, moduli are the four-dimensional manifestation of the existence of extra-dimensions. Since they are only gravitationally coupled, they could decay late in the history of the universe, affecting in a significant way its cosmological evolution. Possible deviations of the cosmological observables from the values predicted by the standard Hot Big Bang Theory constitute an interesting alternative for the discovery of new physics beyond the Standard Model, which is complementary to the particle physics search. For this reason in addition to SUSY-breaking in sequestered models, I also studied several cosmological scenarios arising from them, such as production of non-thermal dark matter and dark radiation, reheating from moduli decay and inflation

Oscillon formation during inflationary preheating with general relativity

We study the non-perturbative evolution of inflationary fluctuations during preheating using fully non-linear general-relativistic field-theory simulations. We choose a single-field inflationary model that is consistent with observational constraints and start the simulations at the end of inflation with fluctuations both in the field and its conjugate momentum. Gravity enhances the growth of density perturbations, which then collapse and virialize, forming long-lived stable oscillon-like stars that reach compactnesses $\mathcal{C}\equiv GM/R \sim 10^{-3}-10^{-2}$. We find that $\mathcal{C}$ increases for larger field models, until it peaks due to the interplay between the overdensity growth and Hubble expansion rates. Whilst gravitational effects can play an important role in the formation of compact oscillons during preheating, the objects are unlikely to collapse into primordial black holes without an additional enhancement of the initial inflationary fluctuations.Comment: 7 pages. 4 figures. Movie: https://youtu.be/vTl9agMfPB0. Matches version published in PR

Non-thermal CMSSM with a 125 GeV Higgs

We study the phenomenology of the CMSSM/mSUGRA with non-thermal neutralino dark matter. Besides the standard parameters of the CMSSM we include the reheating temperature as an extra parameter. Imposing radiative electroweak symmetry breaking with a Higgs mass around 125 GeV and no dark matter overproduction, we contrast the scenario with different experimental bounds from colliders (LEP, LHC), cosmic microwave background (Planck), direct (LUX, XENON100, CDMS, IceCube) and indirect (Fermi) dark matter searches. The allowed parameter space is characterised by a Higgsino-like LSP with a mass around 300 GeV. The observed dark matter abundance can be saturated for reheating temperatures around 2 GeV while larger temperatures require extra non-neutralino dark matter candidates and extend the allowed parameter space. Sfermion and gluino masses are in the few TeV region. These scenarios can be achieved in string models of sequestered supersymmetry breaking which avoid cosmological moduli problems and are compatible with gauge coupling unification. Astrophysics and particle physics experiments will fully investigate this non-thermal scenario in the near future