arXiv subjects

Marco Scalisi

Publications and source records attributed to Marco Scalisi.

At least 19 recordsLinked to original sources

arXiv2026

Quintessential $\alpha$-attractors fit DESI

We study quintessence in $\alpha$-attractor models in light of recent DESI indications for dynamical dark energy. We show that the \emph{knee} of the attractor potential provides an excellent approximation to the axion-like quintessence model used as a DESI benchmark. This leads to a simple relation between the axion decay constant $f_a$ and the attractor parameter $\alpha$, allowing the experimental constraints to be translated into a preference for $\alpha=\mathcal{O}(1)$, in agreement with string-motivated expectations. We solve the background dynamics numerically and find good agreement with the DESI-preferred evolution of $w(z)$ up to $z\sim\mathcal{O}(1)$. More generally, we point out that the agreement between axion-like and attractor potentials reflects a common requirement imposed by the data: today's potential energy and slope are both of order the Hubble scale in Planck units. We finally comment on the origin of the required initial conditions, which can naturally arise in multifield attractor scenarios.

hep-th↗

arXiv2026

Supersymmetry, Large Extra Dimensions and the Gravitino Conjecture

We investigate whether the absence of experimental signals for supersymmetry and extra dimensions can be understood as a correlated phenomenon. Assuming the Gravitino Conjecture, we study the relation between the gravitino mass and the Kaluza-Klein scale in four-dimensional $\mathcal{N}=1$ supergravity from Type II compactifications with large extra dimensions. We parametrize the scaling of the full internal volume with respect to that of a large $p$-cycle through an anisotropy exponent $\alpha$, and derive the corresponding volume contributions to the K\"ahler potential. This leads to constraints on the scaling exponent $n$, linking the gravitino mass to the KK scale, and on the effective number $\alpha p$ of large dimensions. We find that the linear relation $n=1$ is compatible only with one or two large extra dimensions, precisely the cases that can still be probed at micron distances. In such scenarios, micron-sized extra dimensions imply a light gravitino and gauge-mediated supersymmetry breaking, whereas gravity mediation corresponds to compactification scales beyond current experimental reach.

hep-th↗

arXiv2025

Inflationary Particle Production and the Swampland

We investigate the impact of particle production during inflation in scenarios where an infinite tower of states features a mass scale that decreases exponentially along the inflationary trajectory. Such couplings naturally arise in string effective field theories and are in fact motivated by the Swampland Distance Conjecture (SDC). We show that the corrections to inflationary observables sourced by the tower scale as $(H/\Lambda_{\text{sp}})^{2+p}$, with $H$ being the Hubble scale, $\Lambda_{\text{sp}}$ being the species scale, that is the quantum gravity cut-off, and $p\geq 1$ characterizes the density of states in the tower. As a result, in gravitationally weakly coupled cosmological effective theories, the tower-induced contributions are suppressed relative to the standard single-field predictions, leaving the inflationary phenomenology essentially unchanged. We demonstrate this explicitly across a set of well-motivated inflationary potentials, and we compare the resulting predictions with the most recent observational constraints, including those from the Atacama Cosmology Telescope.

hep-th↗

arXiv2025

Bulk/boundary Modular Quintessence and DESI

The latest DESI DR2 results, when combined with other independent cosmological data on the Cosmic Microwave Background and supernovas, suggest a preference for dynamical dark energy. We propose a novel cosmological scenario, which features two distinct scalar fields. One governs the magnitude of the present-day dark energy density and is related to the size of extra-dimensions. Accounting for the observed smallness of this energy density requires the scalar to reside near the boundary of field space. The second field, responsible for the time evolution of dark energy and associated with the string coupling, must instead lie in the bulk to remain consistent with the non-observation of light string states. We show that a natural candidate for such dark energy dynamics is a quintessence modular-invariant potential, in which the second scalar field rolls down a negatively curved slope, starting from a self-dual critical point. We find that this scenario is in good agreement with the latest findings by DESI.

hep-th↗

arXiv2025

On the Origin of Species Thermodynamics and the Black Hole - Tower Correspondence

Species thermodynamics has been proposed in analogy to black hole thermodynamics. The entropy scales like an area and is given by the mere counting of the number of the species. In this work, we $\textit{derive}$ the constitutive relations of species thermodynamics and explain how those $\textit{originate}$ from standard thermodynamics. We consider configurations of species in thermal equilibrium inside a box of size $L$, and show that the temperature $T$ of the system, which plays a crucial role, is always upper bounded above by the species scale $Λ_{\rm sp}$. We highlight three relevant regimes: (i) when $L^{-1}< T<Λ_{\rm sp}$, and gravitational collapse is avoided, the system exhibits standard thermodynamics features, for example, with the entropy scaling like the volume of the box; (ii) in the limit $L^{-1}\simeq T\rightarrow Λ_{\rm sp}$ we recover the rules of species thermodynamics with the entropy scaling like the area of the box; (iii) an intermediate regime with $ L^{-1}\simeq T< Λ_{\rm sp}$ that avoids gravitational collapse and fulfills the Covariant Entropy Bound; this interpolates between the previous two regimes and its entropy is given simply in terms of the counting of the species contributing to the thermodynamic ensemble. This study also allows us to find a novel and independent bottom-up rationale for the Emergent String Conjecture. Finally, we present the $\textit{Black Hole - Tower Correspondence}$ as a generalization of the celebrated Black Hole - String Correspondence. This provides us with a robust framework to interpret the results of our thermodynamic investigation. Moreover, it allows us to qualitatively account for the entropy of black holes in terms of the degrees of freedom of the weakly coupled species in the tower.

hep-th↗

arXiv2024

Starobinsky Inflation in the Swampland

We argue that the Starobinsky model of inflation, realised via an $R^2$ term in the Lagrangian, can originate from quantum effects due to a tower of light species. By means of two separate arguments, we show how this implies that the scale of the $R^2$ term must be of order of the species scale $Λ_s$, namely the energy at which gravity becomes strongly coupled. We discuss the implications and challenges of this scenario for inflation, inflationary reheating, and string theory embeddings. In this context, we collect strong evidence to conclude that Starobinsky inflation lies in the Swampland.

hep-th↗

arXiv2024

Species Scale and Primordial Gravitational Waves

The species scale is a field-dependent UV cut-off for any effective field theory weakly coupled to gravity. In this letter we show that, in the context of inflationary cosmology, a detection of primordial gravitational waves will set an upper bound on the decay rate $|Λ'_s/Λ_s|$ of the species scale. Specifically, we derive this in terms of the tensor-to-scalar ratio $r$ of power spectra of primordial perturbations. Given the targets of current and next generation experiments, we show that any successful detection would signify that this upper limit is of the order of unity, which is consistent with recent discussions in the literature.

hep-th↗

arXiv2023

Primordial black holes and their gravitational-wave signatures

In the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers observed in gravitational wave detectors and an important component of the dark matter in the Universe. Significant progress has been achieved both on the theory side and from the point of view of observations, including new models and more accurate calculations of PBH formation, evolution, clustering, merger rates, as well as new astrophysical and cosmological probes. In this work, we review, analyse and combine the latest developments in order to perform end-to-end calculations of the various gravitational wave signatures of PBHs. Different ways to distinguish PBHs from stellar black holes are emphasized. Finally, we discuss their detectability with LISA, the first planned gravitational-wave observatory in space.

astro-ph.CO↗

arXiv2023

Cosmic Acceleration and Turns in the Swampland

We argue that field trajectories, which lead to cosmic acceleration and feature rapid turns near the boundary of the moduli space, are in the Swampland. We obtain this result by assuming the validity of the Swampland Distance Conjecture (SDC) in the presence of a positive scalar potential and by focusing on hyperbolic spaces, as prototype geometries of infinite distance limits of Calabi-Yau compactifications. We find that, in a quasi-de Sitter space with Hubble rate $H$ and acceleration parameter $ε$, the turning rate $Ω$ is upper bounded such as $Ω/H<\mathcal{O}(\sqrtε)$. Therefore, field trajectories consistent with the SDC can only have a negligible deviation from geodesics. This has direct implications for the realization and consistency of multi-field scenarios in string theory. Moreover, it implies a tension between asymptotic accelerating expansion, consistent with observations, and the de Sitter conjecture.

hep-th↗

arXiv2023

The Scale of Supersymmetry Breaking and the Dark Dimension

We argue for a relation between the supersymmetry breaking scale and the measured value of the dark energy density $Λ$. We derive it by combining two quantum gravity consistency swampland constraints, which tie the dark energy density $Λ$ and the gravitino mass $M_{3/2}$, respectively, to the mass scale of a light Kaluza-Klein tower and, therefore, to the UV cut-off of the effective theory. Whereas the constraint on $Λ$ has recently led to the Dark Dimension scenario, with a prediction of a single mesoscopic extra dimension of the micron size, we use the constraint on $M_{3/2}$ to infer the implications of such a scenario for the scale of supersymmetry breaking. We find that a natural scale for supersymmetry signatures is $M={\cal O}\left(Λ^{1/8}\right)={\cal O}({\rm TeV})$. This mass scale is within reach of LHC and of the next generation of hadron colliders. Finally, we discuss possible string theory and effective supergravity realizations of the Dark Dimension scenario with broken supersymmetry.

hep-th↗

arXiv2023

Early Dark Energy in Type IIB String Theory

Early Dark Energy (EDE) is a promising model to resolve the Hubble Tension, that, informed by Cosmic Microwave Background data, features a generalization of the potential energy usually associated with axion-like particles. We develop realizations of EDE in type IIB string theory with the EDE field identified as either a $C_4$ or $C_2$ axion and with full closed string moduli stabilization within the framework of either KKLT or the Large Volume Scenario. We explain how to achieve a natural hierarchy between the EDE energy scale and that of the other fields within a controlled effective field theory. We argue that the data-driven EDE energy scale and decay constant can be achieved without any tuning of the microscopic parameters for EDE fields that violate the weak gravity conjecture, while for states that respect the conjecture it is necessary to introduce a fine-tuning. This singles out as the most promising EDE candidates, amongst several working models, the $C_2$ axions in LVS with 3 non-perturbative corrections to the superpotential generated by gaugino condensation on D7-branes with non-zero world-volume fluxes.

hep-th↗

arXiv2023

On the correspondence between black holes, domain walls and fluxes

We revisit and extend the correspondence between black holes, domain walls and fluxes in type IIA compactifications. We argue that these three systems can be described by the same supergravity effective action, modulo proper identifications and adjustments. Then, we apply the correspondence to investigate swampland conjectures on de Sitter and anti-de Sitter vacua, as well as on the black hole entropy. We show that, in certain cases, swampland conjectures can be motivated from properties of black hole solutions, such as positiveness of the entropy. This provides a bottom-up rationale which is complementary to the usual tests in string theory. When asking for an agreement between the anti-de Sitter and the black hole entropy distance conjectures, we are led to an extension of the correspondence which includes geometric fluxes and the associated Kaluza-Klein monopoles domain walls. Finally, we point out that the anti-de Sitter distance conjecture is naturally implemented in certain asymptotically anti-de Sitter black holes as a consequence of a constraint involving black hole charges and supergravity gauge couplings.

hep-th↗

arXiv2022

Large and Small Non-extremal Black Holes, Thermodynamic Dualities, and the Swampland

In this paper we discuss black hole solutions parametrized by their entropy $\mathcal{S}$ and temperature $\mathcal{T}$ in gravitational effective theories. We are especially interested in the analysis of the boundary regions in the $\mathcal{T}-\mathcal{S}$ diagram, i.e. large/small values of entropy and temperature, and their relation to Swampland constraints. To explore this correlation, we couple the gravitational theories to scalar fields and connect limits of thermodynamic quantities of black holes to scalar field excursions in the corresponding solutions. Whenever the scalar fields traverse an infinite field distance, the Swampland Distance Conjecture allows for a reformulation in terms of {\it entropy-} or {\it temperature-distance}. The effective theories with scalars we investigate are Einstein-Maxwell-dilaton theory as well as $\mathcal{N} = 2$ supergravity in four dimensions. The relation of the latter to type II string theory compactified on Calabi-Yau 3-folds often allows for a direct identification of the corresponding light tower of states. These setups also point towards various dualities between asymptotic regions of the black hole solution. In the context of $\mathcal{N} = 2$ supergravity black holes, these {\it thermodynamic dualities} have an interpretation in terms of T- and S-dualities along the internal directions and their natural action on Kaluza-Klein and winding states.

hep-th↗

arXiv2022

Towards Early Dark Energy in String Theory

Early Dark Energy (EDE) is a prominent model to resolve the Hubble tension, which employs a dynamical axion with a periodic potential. In this work, we take first steps towards the embedding of this model into stable compactifications of string theory. First, we provide a pedagogical review of the EDE scenario and its main challenges. Second, we construct a simple supergravity toy model using only minimal ingredients. Already at this level, we can understand the origin of the harmonics of the EDE scalar potential in terms of a delicate balance of the leading terms from separate non-perturbative effects. Third and final, we embed the model into a KKLT-type compactification, with the EDE scalar field realized by a two-form axion. We find that a successful embedding, with all moduli stabilized, requires restrictive assumptions both on the Pfaffians and on the exponents of the non-perturbative terms responsible for the EDE dynamics. We point out that such non-generic conditions reflect well known challenges of the EDE model and further investigation might guide us towards a conclusive resolution.

hep-th↗

arXiv2022

Cosmology with the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational wave observations by LISA to probe the universe.

astro-ph.CO↗

arXiv2021

The Gravitino and the Swampland

We propose a new swampland conjecture stating that the limit of vanishing gravitino mass corresponds to the massless limit of an infinite tower of states and to the consequent breakdown of the effective field theory. We test our proposal in large classes of models coming from compactification of string theory to four dimensions, where we identify the Kaluza-Klein nature of the tower of states becoming light. We point out a general relation between the gravitino mass and abelian gauge coupling in models with extended supersymmetry, which can survive also in examples with minimal supersymmetry. This allows us to connect our conjecture to other well established swampland conjectures, such as the weak gravity conjecture or the absence of global symmetries in quantum gravity. We discuss phenomenological implications of our conjecture in (quasi-)de Sitter backgrounds and extract a lower bound for the gravitino mass in terms of the Hubble parameter.

hep-th↗

arXiv2020

Inflation, Higher Spins and the Swampland

We study the implications on inflation of an infinite tower of higher-spin states with masses falling exponentially at large field distances, as dictated by the Swampland Distance Conjecture. We show that the Higuchi lower bound on the mass of the tower automatically translates into an upper bound on the inflaton excursion. Strikingly, the mere existence of all spins in the tower forbids any scalar displacement whatsoever, at arbitrarily small Hubble scales, and it turns out therefore incompatible with inflation. A certain field excursion is allowed only if the tower has a cut-off in spin. Finally, we show that this issue is circumvented in the case of a tower of string excitations precisely because of the existence of such a cut-off, which decreases fast enough in field space.

hep-th↗

arXiv2020

Conifold dynamics and axion monodromies

It has recently been appreciated that the conifold modulus plays an important role in string-phenomenological set-ups involving warped throats, both by imposing constraints on model building and for obtaining a 10-dimensional picture of SUSY-breaking. In this note, we point out that the stability of the conifold modulus furthermore prevents large super- Planckian axion monodromy field ranges caused by brane-flux decay processes down warped throats. Our findings imply a significant challenge for concrete string theory embeddings of the inflationary flux-unwinding scenario.

hep-th↗