arXiv subjects

Ignacio Ruiz

Publications and source records attributed to Ignacio Ruiz.

At least 19 recordsLinked to original sources

arXiv2026

EFT (String) Tower Building

We develop a bottom-up framework to reconstruct the asymptotic spectrum of light towers in four-dimensional $\mathcal{N}=1$ effective field theories directly from their K\"ahler potential. Our construction uses the Integral Scaling Relation, which relates the mass scales of towers becoming light at infinite distance to the tensions of EFT strings, together with the Emergent String Conjecture applied recursively upon decompactification. These conditions organize the tower scaling vectors into a lattice generated by the EFT-string vectors and select the globally consistent tower polytopes. When applied to K\"ahler potentials arising from string compactifications, our algorithm precisely reproduces the known arrangements of towers and duality frames. We then classify the admissible polytopes for asymptotic K\"ahler potentials $K\sim-\log P(s)$, with $P(s)$ a homogeneous polynomial of degree at most seven, and show that certain apparently consistent K\"ahler potentials are incompatible with the assumed quantum-gravity constraints. For general polynomials, additional restrictions arise from gluing the tower arrangements across different growth sectors. Remarkably, every tower polytope allowed by our reconstruction can be obtained as a concrete slice of the polytope associated with M-theory on a Joyce $G_2$-manifold. This provides evidence for a form of string universality in which EFT strings act as the fundamental building blocks of the UV tower structure in the EFT perturbative regimes.

hep-th↗

arXiv2026

A missing link: Brane networks and the Cobordism Conjecture

The absence of global symmetries in a quantum gravity theory often requires the introduction of (new) symmetry-breaking defects, which appear as singular objects in the low-energy description. This has been formalized in the Cobordism Conjecture, which further relates the asymptotics of these defects to non-trivial deformation classes of the effective theory. In this work we investigate the symmetry-breaking defects for theories with a discrete symmetry $G$ encoded in the bordism groups $\Omega^{\xi}_2 (BG)$ and, in particular, its sub-class described in terms of the homology groups $H_2(BG;\mathbb{Z})$. Contrary to expectations we find that the defects are naturally described in terms of networks of codimension-two objects rather than isolated objects in codimension three. While in special situations linking configurations of defects are sufficient, our strategy generically predicts the existence of junctions, thus suggesting an extended applicability of the Cobordism Conjecture. We demonstrate the viability of this approach in four-dimensional supergravity theories originating from string and M-theory with a discrete Heisenberg group acting on its axionic degrees of freedom.

hep-th↗

arXiv2026

Bordisms between 9d type IIB supergravities and commutator widths of duality groups

We study the topological properties of bordisms interpolating between different 9d gauged supergravities obtained from compactification of type IIB string theory on $\mathbb{S}^1$ with a non-trivial $\mathsf{SL}(2,\mathbb{Z})$ bundle. We describe how such bordisms implement the needed monodromies through stacks of $[p,q]$ 7-branes or gravitational solitons of non-trivial topology. For the later mechanism, we see that the topology of the bordism becomes increasingly complicated for large monodromies, which results in the associated bordisms being arbitrarily suppressed, against expectations on the breaking of global symmetries in Quantum Gravity. Motivated by this, we propose a refinement of the Swampland Cobordism Conjecture for the first bordism group $\Omega_1({\rm B}G)$ with a $G$ duality bundle. We argue that even if gravitational solitons can realize the monodromies associated with elements of the commutator subgroup of $G$, if the number of needed commutators is unbounded (in other words, the commutator width of $G$ diverges) then an infinite number of duality defects realizing elements in $G$ need to be included. We test this proposal for different duality groups $G$, and see that our expectations are realized, often in non-trivial ways.

hep-th↗

arXiv2026

Alice in Warpland: KK modes, Warped Compactifications and the Swampland

We investigate the asymptotic behavior of Kaluza-Klein (KK) towers in warped compactifications to Minkowski space. Focusing on the overall decompactification limit, we derive the scaling of KK masses at large KK momentum for scalar fluctuations in lower-dimensional Planck units. In codimension-one warped backgrounds sourced by a higher-dimensional exponential potential, we solve explicitly for the internal profiles and obtain a closed expression for the exponential mass decay rate $\lambda_{\rm KK}$ of the tower in terms of the moduli space distance. We find that warping reduces $\lambda_{\rm KK}$ relative to the unwarped case, in such a way that sufficiently strong warping could in principle violate the Sharpened Distance Conjecture bound. Remarkably, this sharpened bound is still satisfied precisely when the higher-dimensional potential obeys the condition forbidding asymptotic accelerated expansion, establishing a direct link between the Sharpened Distance Conjecture and the Strong de Sitter condition in one higher dimension. We also argue that for higher-codimension warped backgrounds the asymptotic KK scaling remains unmodified.

hep-th↗

arXiv2025

The dark dimension, proton decay, and the length of the M-theory interval

The existence of a large extra dimension in which only gravity propagates would have spectacular consequences for cosmology and laboratory experiments. In the strong coupling limit of the $E_8\times E_8$ heterotic string theory, the gauge and matter fields live at the end of the eleventh dimension, which becomes a natural candidate for a micron-size \textit{dark dimension}. In this work, however, we show that the length of the M-theory interval is severely constrained by proton decay searches. Our results indicate that in such constructions the size of the eleventh dimension is $R\lesssim \mathcal{O}(10^{-28})$ meters.

hep-th↗

arXiv2025

EFT strings and dualities in 4d $\mathcal{N}=1$

We investigate the global structure of the states becoming light at perturbative limits of 4d $\mathcal{N}=1$ string and M-theory compactifications, identifying the different duality frames that emerge asymptotically and how they fit together in moduli space. These limits are characterized by the presence of EFT strings - a special class of axionic BPS strings whose tension, derived from the IR K\"ahler potential, vanishes in Planck units at infinite field distance. An intriguing integer scaling relation, $m \sim \mathcal{T}^w$ with $w = \{1,2,3\}$ in Planck units, connects the tension $\mathcal{T}$ of these strings to the mass scale $m$ of the leading tower of states along the string flow. We show that this relation also holds for the subleading towers below the species scale that generate the tower convex hull, implying that their associated $\vec\zeta = -\vec{\nabla} \log m$ vectors lie in a lattice generated by those of the EFT strings. This reveals a striking UV/IR interplay and offers organizing principles for the parametric hierarchies among the relevant UV scales in a given perturbative limit and the web of dualities governing 4d string vacua.

hep-th↗

arXiv2024

Morse-Bott inequalities, Topology Change and Cobordisms to Nothing

The Cobordism Conjecture predicts spacetime-ending configurations, such as Bubbles of Nothing (BoN), being commonplace. These correspond to vacuum decays in which the compactification manifold $\mathcal{C}_n$ shrinks to a point, with the instability expanding at the speed of light and leaving nothing (not even spacetime) behind. Most constructions of BoN or cobordisms to nothing found in the literature feature simple instances of $\mathcal{C}_n$ or singular cobordisms, which cannot be approached from the effective field theory. Assuming the solution mediating such decay to nothing is homeomorphic to a smooth description, we are able to go a step further, and obtain topological bounds on its homology for generic $\mathcal{C}_n$. Through the use of Morse-Bott theory we then translate this into information on the number and types of topology changes the compact manifold experiences as we move towards the tip of the bordism, as well as the location of possible cobordism defects. We illustrate our results with different detailed examples coming from String Theory. Furthermore, with this approach, we are able to study more complicated arrangements such as BoN collisions or intersection of End of the World branes.

hep-th↗

arXiv2024

Cosmology of light towers and swampland constraints

We study the dynamical evolution of FLRW cosmologies in the presence of a tower of scalar light states and a runaway exponential potential. Some of the attractor solutions have problematic behaviours from the EFT point of view, which we use to argue for restrictions on the possible exponential scalings of the potential and tower characteristic mass as we move towards asymptotic regions in moduli space. These serve as further evidence that the tower mass should not decay faster than the potential or the KK scale associated to the homogeneous decompactification of a single compact dimension. We provide support from different top-down compactifications and connect with previous arguments found in the literature.

hep-th↗

arXiv2024

To curve, or not to curve: Is curvature-assisted quintessence observationally viable?

Single-field models of accelerated expansion with nearly flat potentials, despite being able to provide observationally viable explanations for the early-time cosmic inflation and the late-time cosmic acceleration, are in strong tension with string theory evidence and the associated de Sitter swampland constraints. It has recently been argued that in an open universe, where the spatial curvature is negative (i.e., with $\Omega_k>0$), a new stable fixed point arises, which may lead to viable single-field-based accelerated expansion with an arbitrarily steep potential. Here, we show, through a dynamical systems analysis and a Bayesian statistical inference of cosmological parameters, that the additional cosmological solutions based on the new fixed point do not render steep-potential, single-field, accelerated expansion observationally viable. We mainly focus on quintessence models of dark energy, but we also argue that a similar conclusion can be drawn for cosmic inflation.

hep-th↗

arXiv2024

Cosmological Chameleons, String Theory and the Swampland

We study a scenario with a transient phase of cosmological acceleration that could potentially be realized in asymptotic corners of String Theory moduli space. A very steep scalar potential is temporarily stabilized by the effect of a nonzero density of heavy states, leading to acceleration, in what amounts to a cosmological version of the Chameleon mechanism. The density of heavy states is diluted by cosmological expansion, weakening their effect. After roughly one $e$-fold their effect can no longer stabilize the potential, and the accelerating phase ends. We also study a scenario where there is no potential and the transient acceleration is achieved by the counterbalancing effects of light and heavy towers of states. In both cases we show that it is not possible to obtain more than $\mathcal{O}(1)$ $e$-folds without transplanckian field excursions. We also discuss the general EFT constraints on these models and explore a number of first attempts at concrete embeddings of the scenario in String Theory. These all turn out to face significant challenges.

hep-th↗

arXiv2024

Taxonomy of Infinite Distance Limits

The Emergent String Conjecture constrains the possible types of light towers in infinite-distance limits in quantum gravity moduli spaces. In this paper, we use these constraints to restrict the geometry of the scalar charge-to-mass vectors $(-\vec{\nabla}\log m)$ of the light towers and the analogous vector $(-\vec{\nabla}\log\Lambda_{\text{QG}})$ of the species scale. We derive taxonomic rules that these vectors must satisfy in each duality frame. Under certain assumptions, this allows us to classify the ways in which different duality frames can fit together globally in the moduli space in terms of a finite list of polytopes. Many of these polytopes arise in known string theory compactifications, while others suggest either undiscovered corners of the landscape or new swampland constraints.

hep-th↗

arXiv2023

A Universal Pattern in Quantum Gravity at Infinite Distance

Quantum gravitational effects become significant at a cut-off species scale that can be much lower than the Planck scale whenever we get a parametrically large number of fields becoming light. This is expected to occur at any perturbative limit of an effective field theory coupled to gravity, or equivalently, at any infinite distance limit in the field space of the quantum gravity completion. In this note, we present a universal pattern that links the asymptotic variation rates in field space of the quantum gravity cut-off $\Lambda_{\text{sp}}$ and the characteristic mass of the lightest tower of states $m$: $\frac{\vec\nabla m}{m} \cdot\frac{\vec\nabla \Lambda_{\rm sp}}{ \Lambda_{\rm sp}}=\frac1{d-2}$, where $d$ is the spacetime dimension. This restriction can be used to make more precise several Swampland criteria that constrain the effective field theories that can be consistently coupled to quantum gravity.

hep-th↗

arXiv2023

Stringy Evidence for a Universal Pattern at Infinite Distance

Infinite distance limits in the moduli space of a quantum gravity theory are characterized by having infinite towers of states becoming light, as dictated by the Distance Conjecture in the Swampland program. These towers imply a drastic breakdown in the perturbative regimes of the effective field theory at a quantum gravity cut-off scale known as the species scale. In this paper, we find a universal pattern satisfied in all known infinite distance limits of string theory compactifications, which relates the variation in field space of the mass of the tower and the species scale: $\frac{\vec\nabla m}{m} \cdot\frac{\vec\nabla \Lambda_{\rm sp}}{ \Lambda_{\rm sp}}=\frac{1}{d-2}$ in $d$ spacetime dimensions. This implies a more precise definition of the Distance conjecture and sharp bounds for the exponential decay rates. We provide plethora of evidence in string theory and identify some sufficient conditions that allow the pattern to hold from a bottom-up perspective.

hep-th↗

arXiv2023

A search for pulsars around Sgr A* in the first Event Horizon Telescope dataset

The Event Horizon Telescope (EHT) observed in 2017 the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz ($\lambda$=1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT datasets. The high observing frequency means that pulsars - which typically exhibit steep emission spectra - are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic Center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most-sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the Fast-Folding-Algorithm and single pulse search targeting both pulsars and burst-like transient emission; using the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction ($\lesssim$2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.

astro-ph.HE↗

arXiv2023

Running Decompactification, Sliding Towers, and the Distance Conjecture

We study towers of light particles that appear in infinite-distance limits of moduli spaces of 9-dimensional $\mathcal{N}=1$ string theories, some of which notably feature decompactification limits with running string coupling. The lightest tower in such decompactification limits consists of the non-BPS Kaluza-Klein modes of Type I$'$ string theory, whose masses depend nontrivially on the moduli of the theory. We work out the moduli-dependence by explicit computation, finding that despite the running decompactification the Distance Conjecture remains satisfied with an exponential decay rate $\alpha \ge \frac{1}{\sqrt{d-2}}$ in accordance with the sharpened Distance Conjecture. The related sharpened Convex Hull Scalar Weak Gravity Conjecture also passes stringent tests. Our results non-trivially test the Emergent String Conjecture, while highlighting the important subtlety that decompactification can lead to a running solution rather than to a higher-dimensional vacuum.

hep-th↗

arXiv2023

The FRTB-IMA computational challenge for Equity Autocallables

When the Orthogonal Chebyshev Sliding Technique was introduced it was applied to a portfolio of swaps and swaptions within the context of the FRTB-IMA capital calculation. The computational cost associated to the computation of the ES values - an essential component of the capital caluclation under FRTB-IMA - was reduced by more than $90\%$ while passing PLA tests. This paper extends the use of the Orthogonal Chebyshev Sliding Technique to portfolios of equity autocallables defined over a range of spot underlyings. Results are very positive as computational reductions are of about $90\%$ with passing PLA metrics. Since equity autocallables are a commonly traded exotic trade type, with significant FRTB-IMA computational costs, the extension presented in this paper constitutes an imporant step forward in tackling the computational challenges associated to an efficient FRTB-IMA implementation.

q-fin.RM↗

arXiv2022

Asymptotic Accelerated Expansion in String Theory and the Swampland

We study whether the universal runaway behaviour of stringy scalar potentials towards infinite field distance limits can produce an accelerated expanding cosmology \`{a} la quintessence. We identify a loophole to some proposed bounds that forbid such asymptotic (at parametric control) accelerated expansion in 4d $\mathcal{N}=1$ supergravities, by considering several terms of the potential competing asymptotically. We then analyse concrete string theory examples coming from F-theory flux compactifications on Calabi-Yau fourfolds, extending previous results by going beyond weak string coupling to different infinite distance limits in the complex structure moduli space. We find some potential candidates to yield asymptotic accelerated expansion with a flux potential satisfying $\gamma=\frac{\|\nabla V\|}{V}<\sqrt{2}$ along its gradient flow. However, whether this truly describes an accelerated expanding cosmology remains as an open question until full moduli stabilization including the Kahler moduli is studied. Finally, we also reformulate the condition for forbidding asymptotic accelerated expansion as a convex hull de Sitter conjecture which resembles a convex hull scalar WGC for the membranes generating the flux potential. This provides a pictorial way to quickly determine the asymptotic gradient flow trajectory in multi-moduli setups and the value of $\gamma$ along it.

hep-th↗

arXiv2020

Tensoring volatility calibration

Inspired by a series of remarkable papers in recent years that use Deep Neural Nets to substantially speed up the calibration of pricing models, we investigate the use of Chebyshev Tensors instead of Deep Neural Nets. Given that Chebyshev Tensors can be, under certain circumstances, more efficient than Deep Neural Nets at exploring the input space of the function to be approximated, due to their exponential convergence, the problem of calibration of pricing models seems, a priori, a good case where Chebyshev Tensors can excel. In this piece of research, we built Chebyshev Tensors, either directly or with the help of the Tensor Extension Algorithms, to tackle the computational bottleneck associated with the calibration of the rough Bergomi volatility model. Results are encouraging as the accuracy of model calibration via Chebyshev Tensors is similar to that when using Deep Neural Nets, but with building efforts that range between 5 and 100 times more efficient in the experiments run. Our tests indicate that when using Chebyshev Tensors, the calibration of the rough Bergomi volatility model is around 40,000 times more efficient than if calibrated via brute-force (using the pricing function).

q-fin.RM↗