arXiv subjects

Ivano Basile

Publications and source records attributed to Ivano Basile.

At least 19 recordsLinked to original sources

arXiv2026

String dualities and wedge singularities

We study strings propagating in backgrounds with a wedge singularity, namely whose internal sector describes a wedge sum of closed manifolds. We focus on the wedge sum of two circles, which was recently argued to provide a quantum geometry for an M-theoretic description of type 0 strings, along with a much wider non-supersymmetric duality web stemming from quotients thereof. In the context of this proposal, we investigate whether the worldsheet features of type IIA strings, together with strong-coupling ingredients, can consistently reproduce the expectation of a weakly coupled type 0A frame. To this end, we combine worldsheet effects due to the wedge singularity with the emergence proposal applied to D0-branes probing it. We find that the resulting potential reproduces the correct tree-level mass of the tachyon in a specific scaling limit. We also discuss the possibility of kinematic obstructions to our worldsheet approach using the framework of topological modular forms, and comment on some puzzles and open questions.

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arXiv2026

String theory in the infrared

I briefly summarize a recent research program aiming to probe the landscape of low-energy phases of string theory from a global perspective. Borrowing conceptual lessons from the swampland program, I will discuss how the effective theories of gravity produced by low-energy string theory are far from generic; rather, their infrared data is connected by universal scaling relations which become non-trivial in species limits. In particular, a worldsheet analysis reveals that higher-derivative Wilson coefficients and the vacuum energy exhibit UV/IR relations which are invisible from the viewpoint of effective field theory, leading to parametric inequalities which take the form of holographic bounds. This lends a more solid theoretical support to swampland-motivated phenomenological scenarios, and to the broader hopes of extracting less direct, but empirically accessible, signatures of string theory from cosmological observations.

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arXiv2026

Non-supersymmetric heterotic strings on $AdS_{4}\times S^{3}\times S^{3}$

We analyze the stability properties of a family of anti-de Sitter flux compactifications of the tachyon-free non-supersymmetric heterotic string in ten dimensions. In contrast with simpler such solutions, the solutions include two independent unbounded fluxes, leading to richer instability phenomena. In particular, when the two fluxes are sufficiently close in magnitude, the perturbative spectrum develops tachyonic modes, which can be projected out by an orbifold action. When the fluxes are far apart, tachyonic modes are absent, and the geometry displays inverse scale separation, where a factor of the internal manifold becomes parametrically larger than the anti-de Sitter factor. Still, non-perturbative instabilities in the form of brane nucleation are always available decay channels, and tend to drive the two fluxes closer together, eventually triggering the tachyonic instability when present.

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arXiv2026

UV/IR relations from the worldsheet

We derive universal scaling relations for the low-energy effective action of string theory, connecting the vacuum energy and gauge couplings to higher-derivative Wilson coefficients. At one-loop in string perturbation theory, these generic parametric relations follow from modular and conformal invariance of the worldsheet, independently of the specific low-energy phase of the theory, and they become non-trivial in species limits. As a result, we substantially strengthen our previous case for the emergent string conjecture and connect UV/IR mixing to swampland principles. We argue that our results persist to higher loops, hinting at a pathway to study strong couplings using dualities. Further accounting for open-string contributions, if any, our results lead to parametric inequalities which reproduce holographic bounds and support the magnetic weak-gravity conjecture and the dark dimension scenario.

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arXiv2026

Higher-Spin and Higher-Point Constraints on Stringy Amplitudes

We employ multiparticle factorization to constrain deformations of tree-level open string amplitudes. Assuming minimal degeneracy among intermediate states of the same spin up through the second excited level, we find that the Regge intercept among all amplitudes of the Koba-Nielsen type can be uniquely fixed using seven-point factorization, precisely matching the bosonic string. Moreover, we produce novel constraints on deformations of the worldsheet integrand. We then turn to deformations of superstrings, with massless external states and arbitrary spectral degeneracy, using soft kinematics. Accounting for the infinite tower of higher-spin resonances, we obtain novel multipositivity bounds to leading and subleading order in the large-level limit. We apply these bounds to the simplest factorizable satellite deformation in the family of amplitudes found by Gross, showing that any deformation of four-point string amplitudes of this type is forbidden by unitarity. Our results reinforce the folklore that the higher-spin tower of string excitations is dramatically more rigid than any finite number of species.

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arXiv2025

Instabilities in scale-separated Casimir vacua

Parametric scale separation is notoriously difficult to achieve in flux compactifications of gravitational effective theories. An appealing alternative to conventional Freund-Rubin vacua involves Ricci-flat internal manifolds, where the energy supplied by fluxes is balanced not by curvature but by the Casimir energy. The internal volume can be stabilized by this mechanism producing anti-de Sitter geometries with parametric scale separation, including an explicit example in eleven-dimensional supergravity. We study deformations of these geometries, showing the presence of perturbative and non-perturbative instabilities.

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arXiv2025

Non-supersymmetric branes and discrete topological terms

In a recent work, Tachikawa and Zhang proved the existence of a discrete topological term in the unique non-supersymmetric heterotic string with no tachyons in ten dimensions. This theory features NS5-branes, whose chiral degrees of freedom are not well-understood due to the absence of dualities or supersymmetry. In this paper, we test the consistency of a tentative spectrum obtained by anomaly inflow, studying the relation between the worldvolume theory and the discrete topological term in spacetime. Furthermore, we conduct a bottom-up investigation of lower-dimensional gravitational theories with the same methods.

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arXiv2025

Dark bubble cosmology and the equivalence principle

The main goal of string phenomenology is to find realistic models of particle physics and cosmology within string theory. Dark bubble cosmology is an alternative to string compactifications, where our universe lives on a bubble expanding in a higher-dimensional spacetime. This construction is inherently non-supersymmetric and can yield a four-dimensional realistic cosmology, where radiation behaves as expected due to its coupling to higher-dimensional fields. We study the coupling of the electroweak and strong sectors to the induced braneworld gravity via the same mechanism. While the electroweak sector is unaffected, the gravitational and inertial masses of the proton differ significantly, severely violating measurements of the equivalence principle.

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arXiv2025

Center Symmetry Breaking in Calabi--Yau Compactifications

It is widely believed that global symmetries must be broken in Quantum Gravity. This includes higher-form symmetries, which are commonplace in supergravity coupled to vector multiplets. Recently, a quantitative criterion for the breaking of (higher-form) symmetries in effective field theories of gravity has been proposed. We studied this criterion in the context of center one-form symmetries broken by BPS states in Calabi--Yau compactifications of type IIA string theory and M-theory. In a simple toy model, we evaluated the parameters quantifying the extent of symmetry breaking for large and small values of the moduli, comparing the scales of significant breaking with other relevant physical scales.

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arXiv2025

Corrections to the CRV pattern

We investigate a pattern in the string landscape recently discovered by Castellano, Ruiz and Valenzuela, extending the analysis to subleading order in some calculable infinite-distance limits of supersymmetric compactifications. We find that in the investigated setups the proposed relation between the (gradients of the) mass gap of light towers and the species scale is satisfied. Moreover, we study an analogous relation between the species scale and the recently proposed black-hole scale, which can detect the mass gap of light species via black-hole thermodynamics. We find that, while the slope of the species scale is uniformly bounded as expected, the inner products involving the mass gap does not obey an analogous bound. Replacing the mass gap by the black-hole scale introduces subtleties, preventing us from drawing the same conclusion.

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arXiv2025

Dynamical dark energy in 0'B braneworlds

We build a novel realization of dark bubble cosmology in non-supersymmetric string theory. Among the simplest models in ten dimensions, the type 0'B orientifold is the unique option which yields a scale-separated construction. The resulting setting produces a logarithmically varying dynamical dark energy, reflecting its holographic counterpart in terms of running gauge couplings. We analyze in detail the phenomenological consequences of the model for particle physics, inflation and late-time cosmology. We find that, although particle physics may be consistently realized, neither early-time nor late-time are observationally viable.

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arXiv2025

Asymptotic safety, quantum gravity, and the swampland: a conceptual assessment

We provide a conceptual assessment of some aspects of fundamental quantum field theories of gravity in light of foundational aspects of the swampland program. On the one hand, asymptotically safe quantum gravity may provide a simple and predictive framework, thanks to a finite number of relevant parameters. On the other hand, a (sub-)set of intertwined swampland conjectures on the consistency of quantum gravity can be argued to be universal via effective field theory considerations. We answer whether some foundational features of these frameworks are compatible. This involves revisiting and refining several arguments (and loopholes) concerning the relation between field-theoretic descriptions of gravity and general swampland ideas. We identify the thermodynamics of black holes, spacetime topology change, and holography as the core aspects of this relation. We draw lessons on the features that a field theoretic description of gravity must (not) have to be consistent with fundamental principles underlying the swampland program, and on the universality of the latter.

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arXiv2024

Visions in Quantum Gravity

To deepen our understanding of Quantum Gravity and its connections with black holes and cosmology, building a common language and exchanging ideas across different approaches is crucial. The Nordita Program "Quantum Gravity: from gravitational effective field theories to ultraviolet complete approaches" created a platform for extensive discussions, aimed at pinpointing both common grounds and sources of disagreements, with the hope of generating ideas and driving progress in the field. This contribution summarizes the twelve topical discussions held during the program and collects individual thoughts of speakers and panelists on the future of the field in light of these discussions.

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arXiv2024

Lectures in Quantum Gravity

Formulating a quantum theory of gravity lies at the heart of fundamental theoretical physics. This collection of lecture notes encompasses a selection of topics that were covered in six mini-courses at the Nordita PhD school "Towards Quantum Gravity". The scope was to provide a coherent picture, from its foundation to forefront research, emphasizing connections between different areas. The lectures begin with perturbative quantum gravity and effective field theory. Subsequently, two ultraviolet-complete approaches are presented: asymptotically safe gravity and string theory. Finally, elements of quantum effects in black hole spacetimes are discussed.

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arXiv2024

Banks-Zaks Stabilisation of Non-SUSY Strings

It appears to be difficult within string theory to obtain genuine scale separation between spacetime and the internal sector. In this paper, we propose a novel mechanism for scale-separated vacua which hinges on stringy effects that are invisible at the level of effective field theory. We show that (meta)stable vacua can form if a super no-scale one-loop potential combines with generic two-loop contributions to the vacuum energy, in a manner analogous to Banks-Zaks fixed points. Weak string coupling and scale separation arise from the accidental smallness of the one-loop term, which receives contributions only from massive states, relative to the two-loop term. We provide a proof of concept of this mechanism in explicit non-supersymmetric heterotic toroidal orbifolds by balancing the complete one-loop contribution against the estimated two-loop term and numerically minimizing the resulting effective potential in a restricted sector of moduli space. We note that this mechanism is generically possible within any fundamental theory that has a one-loop energy that gets contributions only from massive modes.

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arXiv2024

Dark dimension with (little) strings attached

We motivate a relation between dark energy and the scale of new physics in weakly coupled string theory. This mixing between infrared and ultraviolet physics leads to a unique corner for real-world phenomenology: barring fine-tunings, we are naturally led to the ``dark dimension'' scenario, a single mesoscopic extra dimension of micron size with the standard model localized on D-branes. Our explicit top-down worldsheet derivation establishes it on a more solid grounding. Allowing some fine-tuning, such that the vacuum energy only arise at higher orders in string perturbation theory, the ``little string theory'' scenario with a very weakly coupled string is an alternative possibility. In this case, the string scale lies at the edge of detectability of particle accelerators.

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arXiv2024

Species scale, worldsheet CFTs and emergent geometry

We study infinite-distance limits in the moduli space of perturbative string vacua. The remarkable interplay of string dualities seems to determine a highly non-trivial dichotomy, summarized by the emergent string conjecture, by which in some duality frame either internal dimensions decompactify or a unique critical string becomes tensionless. We investigate whether this pattern persists in potentially non-geometric settings, showing that (a proxy for) the cutoff of the gravitational effective field theory in perturbative type II vacua extracted from a graviton scattering amplitude vanishes if and only if a light tower of states appears. Moreover, under some technical assumptions on the spectrum of conformal weights, the cutoff scales with the spectral gap of the internal conformal field theory in the same manner as in decompactification or emergent string limits, regardless of supersymmetry or whether the internal sector is geometric. As a byproduct, we elucidate the role of the species scale in (de)compactifications and show compatibility between effective field theory and worldsheet approaches in geometric settings with curvature.

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arXiv2024

Minimal Black Holes and Species Thermodynamics

The species scale provides a lower bound on the shortest possible length that can be probed in gravitational effective theories. It may be defined by the size of the minimal black hole in the theory and, as such, it has recently been given an interpretation along the lines of the celebrated black hole thermodynamics. In this work, we extend this interpretation to the case of charged species. We provide working definitions of minimal black holes for the case of uncharged and charged species constituents. Then, examining the modifications in the thermodynamic properties of near-extremal charged species compared to the uncharged case, we uncover interesting implications for the cosmology of an expanding universe, particularly within the context of the Dark Dimensions Scenario. Finally, we explore possible microscopic constructions in non-supersymmetric string theories in which towers of charged near-extremal species may arise.

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