arXiv subjects

Saul Ramos-Sanchez

Publications and source records attributed to Saul Ramos-Sanchez.

At least 19 recordsLinked to original sources

arXiv2026

A multi-axion model of inflation and dark matter

Models with extra dimensions include a tower of massive states that unavoidably contribute to cosmological dynamics. In particular, after compactification, a higher-dimensional axion gives rise to a set of states whose dynamics at early times exhibit the properties of inflation and, at late times, those of dynamical dark matter. Interestingly, natural choices of parameters imply that the inflationary trajectory in field space is approximately geodesic, meaning that inflation is effectively driven by a single inflaton corresponding to the heaviest state. In this scenario, all inflationary observables, including the emerging spectral distortions, are consistent with current observational constraints, and exact numerical solutions of the equations of motion show that reheating can consistently proceed down to temperatures of a few MeV. Furthermore, all states lighter than the inflaton only come to dominate the energy density of the Universe during the matter-dominated era, thus behaving as dark matter at late times. These states undergo a cascade of decays into radiation, while maintaining a sufficient dark-matter abundance to account for the observed relic density. The lightest dark-matter candidate remains stable on timescales far exceeding the age of the Universe, thereby satisfying even the most conservative observational constraints.

hep-ph↗

arXiv2026

Rolling with modular symmetry: quintessence and de Sitter in heterotic orbifolds

Modular invariance is a fundamental symmetry in string compactifications, constraining both the structure of the effective theory and the dynamics of moduli and matter fields. It has also gained renewed importance in the context of swampland conjectures and, independently, flavour physics. We investigate a modular-invariant scalar potential arising from heterotic orbifolds, where the flavour structure and moduli dynamics are jointly shaped by the underlying geometry. Focusing on a string-inspired, two-moduli truncation, we uncover a rich vacuum structure featuring anti-de Sitter minima and unstable de Sitter saddle points. We identify large regions in moduli space supporting multifield hilltop quintessence consistent with observations. All solutions satisfy refined swampland de Sitter bounds. Our results illustrate how modular symmetry can guide the construction of controlled, string-motivated quintessence scenarios within consistent effective theories.

hep-th↗

arXiv2025

Demystifying stringy miracles with eclectic flavor symmetries

Effective field theories arising from string compactifications are subject to constraints originating from the duality transformations of string theory. Interpreting these so-called selection rules in terms of conventional symmetries has remained challenging. We show that particular selection rules in heterotic orbifolds can be explained from a subtle interplay between modular and traditional flavor symmetries within the eclectic flavor framework.

hep-th↗

arXiv2025

Quark and lepton masses

Quarks and leptons, the fundamental building blocks of the subatomic world, manifest in three families - replicas with identical quantum numbers that differ only in their masses. After summarizing the present data, an overview is presented of the main attempts to explain the origin of the observed patterns and trace it back to an as-yet-unknown fundamental principle.

hep-ph↗

arXiv2025

Non-Abelian orbifolds of the SO(32) heterotic string

Non-Abelian toroidal heterotic orbifolds have received comparatively little attention, mainly because of the significant computational challenges they pose, even at the level of computing their matter spectrum. Similarly, the SO(32) heterotic string remains relatively unexplored. In this paper, we provide some useful tools to handle this situation. We find that certain non-Abelian orbifolds can be studied using the techniques that are common to Abelian compactifications. In such cases, we show how to compute the gauge groups and massless matter spectrum for non-Abelian orbifolds of the SO(32) heterotic string with standard embedding. A general feature of these constructions is the reduction of the rank of the gauge group. Our findings motivate further research on non-Abelian orbifolds with non-standard embedding, where realistic, rank-reduced models are expected to emerge.

hep-th↗

arXiv2025

The Non-SUSY Orbifolder: a tool to build promising non-supersymmetric string models

We introduce the non-SUSY orbifolder, which is a program developed in C++ that computes the low-energy effective theory of non-supersymmetric heterotic orbifold compactifications. The program includes routines to compute the massless spectrum, to automatically generate large sets of orbifold models, to identify phenomenologically interesting models (e.g. models sharing features of the Standard Model (SM) or Grand Unified Theories (GUT)) and to analyze their vacuum configurations.

hep-th↗

arXiv2025

Multiple realizations of modular flavor symmetries and their phenomenology

We point out that specifying the finite modular group does not uniquely fix a modular flavor symmetry. We illustrate this using the finite modular group $T'$. Otherwise equivalent models based on different $T'$ lead to modular forms with different properties and, hence, produce different phenomenological features. We exemplify this in various scenarios, and show that the ability of a given model to accommodate mass and other observed hierarchies depends sensitively on the way the $T'$ is implemented.

hep-ph↗

arXiv2024

Modular flavored dark matter

Discrete flavor symmetries have been an appealing approach for explaining the observed flavor structure, which is not justified in the Standard Model (SM). Typically, these models require a so-called flavon field in order to give rise to the flavor structure upon the breaking of the flavor symmetry by the vacuum expectation value (VEV) of the flavon. Generally, in order to obtain the desired vacuum alignment, a flavon potential that includes additional so-called driving fields is required. On the other hand, allowing the flavor symmetry to be modular leads to a structure where the couplings are all holomorphic functions that depend only on a complex modulus, thus greatly reducing the number of parameters in the model. We show that these elements can be combined to simultaneously explain the flavor structure and dark matter (DM) relic abundance. We present a modular model with flavon vacuum alignment that allows for realistic flavor predictions while providing a successful fermionic DM candidate.

hep-ph↗

arXiv2024

The eclectic flavor symmetries of $\mathbb{T}^2/\mathbb{Z}_K$ orbifolds

Only four $\mathbb{T}^2/\mathbb{Z}_K$ orbifold building blocks are admissible in heterotic string compactifications. We investigate the flavor properties of all of these building blocks. In each case, we identify the traditional and modular flavor symmetries, and determine the corresponding representations and (fractional) modular weights of the available massless matter states. The resulting finite flavor symmetries include Abelian and non-Abelian traditional symmetries, discrete $R$ symmetries, as well as the double-covered finite modular groups $(S_3\times S_3)\rtimes\mathbb{Z}_4$, $T'$, $2D_3$ and $S_3\times T'$. Our findings provide restrictions for bottom-up model building with consistent ultraviolet embeddings.

hep-th↗

arXiv2024

Flavor's Delight

Discrete flavor symmetries provide a promising approach to understand the flavor sector of the standard model of particle physics. Top-down (TD) explanations from string theory reveal two different types of such flavor symmetries: traditional and modular flavor symmetries that combine to the eclectic flavor group. There have been many bottom-up (BU) constructions to fit experimental data within this scheme. We compare TD and BU constructions to identify the most promising groups and try to give a unified description. Although there is some progress in joining BU and TD approaches, we point out some gaps that have to be closed with future model building.

hep-th↗

arXiv2024

Quark and lepton modular models from the binary dihedral flavor symmetry

Inspired by the structure of top-down derived models endowed with modular flavor symmetries, we investigate the yet phenomenologically unexplored binary dihedral group 2D_3. After building the vector-valued modular forms in the representations of 2D_3 with small modular weights, we systematically classify all (Dirac and Majorana) mass textures of fermions with fractional modular weights and all possible 2+1-family structures. This allows us to explore the parameter space of fermion models based on 2D_3, aiming at a description of both quarks and leptons with a minimal number of parameters and best compatibility with observed data. We consider the separate possibilities of neutrino masses generated by either a type-I seesaw mechanism or the Weinberg operator. We identify a model that, besides fitting all known flavor observables, delivers predictions for six not-yet measured parameters and favors normal-ordered neutrino masses generated by the Weinberg operator. It would be interesting to figure out whether it is possible to embed our model within a top-down scheme, such as T2/Z4 heterotic orbifold compactifications.

hep-ph↗

arXiv2024

Spectral distortions from promising single and multifield inflationary models

Forthcoming missions probing the absolute intensity of the CMB are expected to be able to measure spectral distortions, which are deviations from its blackbody distribution. As cosmic inflation can induce spectral distortions, these experiments offer a possibility to further test the various promising inflationary proposals, whose predictions need to be carefully determined. After numerically fitting all inflationary observables to match current observations, we compute the predicted spectral distortions of various promising single and multifield inflationary models. The predictions of single-field inflationary models display deviations between 0.5% and 20% with respect to the standard cosmological model in the observable window, where multi-natural and axion-monodromy inflation stand out in this respect. In the case of multifield inflation, we observe a richer structure of the power spectrum, which, in the case of so-called hybrid attractors, yields spectral distortions about 100 times more intense than the standard signal. These observations open up questions about the relation among our results and other cosmological observables that are also to be probed soon, such as the production of primordial black holes and gravitational waves.

astro-ph.CO↗

arXiv2024

An autoencoder for heterotic orbifolds with arbitrary geometry

Artificial neural networks have become important to improve the search for admissible string compactifications and characterize them. In this paper we construct the heterotic orbiencoder, a general deep autoencoder to study heterotic orbifold models arising from various Abelian orbifold geometries. Our neural network can be easily trained to successfully encode the large parameter space of many orbifold geometries simultaneously, independently of the statistical dissimilarities of their training features. In particular, we show that our autoencoder is capable of compressing with good accuracy the large parameter space of two promising orbifold geometries in just three parameters. Further, most orbifold models with phenomenologically appealing features appear in bounded regions of this small space. Our contribution hints towards a possible simplification of the classification of (promising) heterotic orbifold models.

hep-th↗

arXiv2024

Heterotic Orbifold Models

We review efforts in string model building, focusing on the heterotic orbifold compactifications. We survey how one can, starting from an explicit string theory, obtain models which resemble Nature. These models exhibit the standard model gauge group, three generations of standard model matter and an appropriate Higgs sector. Unlike many unified models, these models do not suffer from problems such as doublet-triplet splitting, too rapid proton decay and the $μ$ problem. Realistic patterns of fermion masses emerge, which are partly explained by flavor symmetries, including their modular variants. We comment on challenges and open questions.

hep-th↗

arXiv2023

The simplest case of dark inflaxion

Dark matter and cosmic inflation represent two of the major puzzles in cosmology. They are typically addressed by introducing separate fields with independent dynamics. On the other hand, extra dimensions might play an important role for observable physics. We introduce a five-dimensional model called dark inflaxion that includes an axion-like particle, whose Kaluza-Klein modes can describe inflation and dark matter. We show that a simple yet natural choice of the mass scale of the effective four-dimensional fields of our model can accommodate simultaneously the observable values of inflationary parameters and dark-matter abundance. It will be interesting to explore the consequences and predictions of more generic scenarios within the scope of our model, which include the possibility of multifield inflation and dark matter.

hep-ph↗

arXiv2023

The Flavor Puzzle: Textures and Symmetries

We discuss aspects of a promising top-down origin of flavor symmetries in particle physics. Modular transformations originating from string theory dualities are shown to play a crucial role. We introduce the notion of an "eclectic" flavor scheme that unifies traditional flavor symmetries, modular symmetries and CP-transformations. It exhibits the phenomenon of "Local Flavor Unification" with enhanced flavor symmetries at fixed points or lines in moduli space. Successful fits of masses and mixing angles of quarks and leptons are found in the vicinity of these points and lines.

hep-ph↗

arXiv2023

Higgs-portal dark matter from non-supersymmetric strings

Large classes of non-supersymmetric string models equipped with standard-model features have been constructed, but very little of their phenomenology is known. Interestingly, their spectra exhibit scalar fields whose only couplings to observed particles is through a multi-Higgs sector. On the other hand, bottom-up models with Higgs portals offer still an acceptable framework for dark matter. We explore realizations of such Higgs portals in promising heterotic orbifold models without supersymmetry. We find that a sample model includes Higgs vacua that are stable at one-loop, in which the Higgs sector is compatible with particle-physics observations and a scalar can account for the measured dark matter abundance. In such vacua, interesting constraints on the masses of the dark matter candidate and the heavy Higgs sector are uncovered. These compelling results are not limited to string models, as they can be embedded in similarly motivated bottom-up schemes.

hep-ph↗

arXiv2023

Matter matters in moduli fixing and modular flavor symmetries

Modular flavor symmetries provide us with a very compelling approach to the flavor problem. It has been argued that moduli values close to some special values like $τ=i$ or $τ=ω$ provide us with the best fits to data. We point out that the presence of hidden "matter" fields, needed to uplift symmetric AdS vacua, gives rise to a dynamical mechanism that leads to such values of $τ$.

hep-th↗