arXiv subjects

Mariano Quiros

Publications and source records attributed to Mariano Quiros.

At least 19 recordsLinked to original sources

arXiv2026

The linear dilaton in cosmology and particle physics

A warped extra dimension in a five-dimensional (5D) anti de Sitter (AdS) background was introduced in 1999 by Lisa Randall and Raman Sundrum to solve the gauge hierarchy problem in particle physics. As a bonus, a holographic interpretation in terms of four dimensional (4D) conformal field theories (CFT) was found. Interestingly enough, another 5D background, the linear dilaton (LD), was found to have a holographic interpretation in terms of Little String Theory. In this review we will show how a set of 5D backgrounds, parametrized in terms of a real parameter $ν$, generalizes both theories and gives rise, in particular, to AdS for $ν=0$ and to LD for $ν=1$. Furthermore, working in the 5D theory, we will consider applications of the LD background to: i) Particle Physics, so that the 5D Planck scale can be lowered to sub-Planckian values, ii) Brane World Cosmology (BWC), based on the appearance of an extra vacuum characterized by a 5D black hole. In all cases we find a gapped continuum for bulk propagating fields, which makes connection with unparticles. In the case of BWC we also point out on the existence of a pressureless holographic fluid which could play the role of dark matter (DM), with feeble (gravitational) interactions to the Standard Model (SM), decoupled from the thermal SM bath, and generated by a freeze-in mechanism after inflation. We also point out the additional possibility of identifying DM with a long-lived feebly interacting massive graviton, as an isolated resonance generated by radiative corrections to the continuum graviton propagator self-energy.

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arXiv2026

Massive Graviton Dark Matter from a Gapped Continuum

We consider the possibility of dark matter in a warped extra-dimensional theory in presence of a linear dilaton background, with a gapped continuum spectrum, in a brane-world cosmological scenario. Firstly, triggered by self-energy radiative corrections, we study the existence of an isolated resonance of massive gravitons, and its realization as a long-lived feebly interacting dark matter candidate, produced by the freeze-in mechanism. This massive graviton is proved to satisfy all theoretical and experimental constraints, in the sub-MeV mass range. We further consider the close relationship between the existence of this component of dark matter and the presence of an inflaton localized on the brane, with a mass around $10^{11}$ GeV and a sub-TeV reheating temperature, in a brane inflationary scenario that allows to reproduce the most recent cosmological observables. Secondly, the gapped continuum of gravitons, a particular five dimensional realization of the physics of unparticles, is identified as a holographic fluid which can play the role of holographic dark matter. The production of the holographic fluid goes by an ultra-violet freeze-in mechanism, with an abundance mainly depending on the reheating temperature. Depending on the values of the mass gap and the reheating temperature, one or both components of dark matter can be present.

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arXiv2026

Gauge coupling unification and doublet-triplet splitting via GUT dynamical breaking

An interesting framework to achieve gauge coupling unification consists in adding to the Standard Model Lagrangian non-renormalizable operators of $d \geq 5$, which affect the kinetic term of gauge fields. We first review the phenomenology related to this framework in the context of $SU(5)$, identifying which are the most interesting representations for the sake of achieving coupling unification. Secondly, we point out that in the case of a dynamical breaking pattern, it is possible to relate gauge coupling unification with the doublet-triplet splitting problem. We show that condensates of fermions in the $5$ representation do not lead to viable models because of proton decay constraints. At difference, we point out that successful models can be obtained by considering condensates of fermions in the $10$, as well as in the $24$ representations.

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arXiv2026

The Standard Model partial unification scale as a guide to new physics model building

In the Standard Model, partial unification of the non-Abelian running gauge couplings is achieved at the scale $μ^{SM}_{32} \approx 2.8 \times 10^{16}$ GeV. Elaborating on this fact, we discuss a simple general parametrization for the new physics corrections leading to full unification at some scale $M_X$. We show that for any new physics model such that the corrections to the non-Abelian couplings are equal (or nearly so), $M_X$ is equal (or close to) the partial unification scale $μ^{SM}_{32}$; the latter scales could be disentangled only if the corrections to the non-Abelian couplings are significantly different. We explore how the parametrization works for some relevant models with new physics below $M_X$, as low energy supersymmetry, split supersymmetry, etc. As for models with a desert up to $M_X$, we explore in particular how the parametrization works for string inspired corrections; we find a phenomenologically remarkable possibility for unification at about 100 TeV, suggesting a low string scale, in addition to the more conservative possibility for unification at $μ^{SM}_{32}$; for models with power-low running/threshold corrections, we also outline an interesting connection with the number of fermion families propagating in the bulk.

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arXiv2026

Stable Black Strings from Warped Backgrounds

We show that spacetime curvature alone can classically stabilize black strings. Working within a consistent five-dimensional dilaton-gravity system with a flat brane, we find that sufficiently large black strings are classically stable when they extend from the brane to a timelike boundary, which may be either regular or conformal. Black strings are also classically stable in the critical case of the linear dilaton spacetime. In some of the curved backgrounds considered, black strings are stable despite having infinite horizon area.

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arXiv2026

Holographic Dark Matter

Cold dark matter may be a fluid (or plasma) residing in a strongly-interacting hidden sector, rather than a population of weakly-coupled particles. Such a scenario admits a holographic description in terms of a cosmological braneworld embedded in the linear dilaton five-dimensional (5D) spacetime. In this framework, dark matter originates from the linear dilaton bulk black hole, whose phase we show to be thermodynamically favored at all temperatures. We present a natural freeze-in mechanism for the production of holographic dark matter, in which the bulk black hole is fed by energy leaking from the brane after inflation. Our model is characterized by two free parameters, one of which, the position of the black hole horizon, is fixed by the observed dark matter abundance. The remaining parameter, the 5D Planck scale $M_5$, is consistent with all current experimental bounds provided that $M_5\gtrsim 3\times 10^5$ TeV.

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arXiv2025

Complementary Probes of Warped Extra Dimension: Colliders, Gravitational Waves and Primordial Black Holes from Phase Transitions

We study the formation of primordial black holes (PBHs) and stochastic gravitational waves background (SGWB) produced by the supercooled radion phase transition (PT) in warped extra-dimension models solving the gauge hierarchy problem. We first determine how the SGWB and the produced PBH mass and abundance depend on the warped model's infrared energy scale $ρ$, and the number of holographic colors $N$. With this finding, we recast on the plane $\{ρ, N\}$ the current SGWB and PBH constraints, as well as the expected parameter reaches of GW detectors, as LISA and ET, and the gravitational lensing ones, such as NGRST. On the same plane, we also map the collider bounds on massive graviton production, and cosmological bounds on the radion phenomenology. We find that, for $N \sim 10-50$, the considered PT predicts a PBH population mass in the range $M_{\rm PBH}\sim(10^{-1} - 10^{-25}) M_{\odot}$ for $ρ\sim (10^{-4} - 10^{8})\textrm{ TeV}$. In the range $ρ\simeq (0.05 - 0.5)$ GeV, it can explain the recent SGWB hint at nHz frequencies and generate PBH binaries with mass $M_{\rm PBH}\sim(0.1 - 1 ) M_\odot$ detectable at LISA and ET. The experimentally allowed mass region where PBHs can account for the whole dark matter abundance, and are produced with a tuning $\lesssim 10^{-4}$, corresponds to $10$ TeV $\lesssim ρ\lesssim$ $10^4$ TeV. These PBHs can compensate the lack of natural candidates for dark matter in warped extra dimensional models. Such a region represents a great science case where forthcoming and future colliders like HE-LHC and FCC-hh, gravitational-wave observatories and other PBHs probes play a key complementary role.

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arXiv2025

Entanglement Entropy and Thermal Phase Transitions from Curvature Singularities

We study holographic entanglement entropy and revisit thermodynamics and confinement in the dilaton-gravity system. Our analysis focuses on a solvable class of backgrounds that includes AdS and linear dilaton spacetimes as particular cases, with some results extended to general warped metrics. A general lesson is that the behavior of the holographic theory is tied to the bulk curvature singularities. We find that a singular background is confining if and only if i) the singularity coincides with a boundary or ii) it is the linear dilaton. In the former case, for which the singularity cuts off spacetime, we demonstrate that both entanglement entropy and thermodynamics exhibit a first order phase transition. In the linear dilaton case we find instead that both entanglement entropy and thermal phase transitions are of second order. Additionally, along the process we thoroughly derive the radion effective action at quadratic order.

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arXiv2025

An introduction to effective potential methods in field theory

In this chapter we give a pedagogical introduction to effective potential methods in field theories. We first review the general functional methods leading to the concept of effective action and effective potential. Focusing on the effective potential we review the methods to compute radiative contributions, starting from the original 1973 seminal paper by Sidney Coleman and Erick Weinberg on one-loop corrections, along with its improvement by the renormalization group equations, as well as some basic results from thermal field theory, including the one-loop thermal corrections to the effective potential. We concentrate on some physical applications of the effective potential: i) the possibility of spontaneous symmetry breaking by radiative corrections, ii) the metastability of the electroweak vacuum in the Standard Model, and iii) the relevance of quantum effects in the dynamics of Higgs inflation. We then apply the previous results to cosmological phase transitions in the early universe and the possibility of generating a stochastic background of gravitational waves as well as primordial black holes.

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arXiv2024

On electroweak metastability and Higgs inflation

For the central values of the relevant experimental inputs, that is the strong coupling constant and the top quark and Higgs masses, the effective Higgs potential displays two minima, one at the electroweak scale and a deeper one at high energies. We review the phenomenology of the Higgs inflation model, extending the Standard Model to include a non-minimal coupling to gravity; as recently shown [1], even configurations that would be metastable in the Standard Model, become viable for inflation if the non-minimal coupling is large enough to flatten the Higgs potential at field values below the barrier between the minima.

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arXiv2024

Electroweak metastability and Higgs inflation

Extrapolating the Standard Model Higgs potential at high energies, we study the barrier between the electroweak and Planck scale minima. The barrier arises by taking the central values of the relevant experimental inputs, that is the strong coupling constant and the top quark and Higgs masses. We then extend the Standard Model by including a non-minimal coupling to gravity, and explore the phenomenology of the Higgs inflation model. We point out that even configurations that would be metastable in the Standard Model, become viable for inflation if the non-minimal coupling is large enough to flatten the Higgs potential at field values below the barrier; we find that the required value of the non-minimal coupling is smaller than the one needed for the conventional Higgs inflation scenario (which relies on a stable Standard Model Higgs potential, without any barrier); in addition, values of the top mass which are slightly larger than those required in the conventional scenario are allowed.

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arXiv2024

Dark Branes for Dark Matter

We propose a setup for the origin of dark matter based on spacetime with a warped extra dimension and three branes: the Planck brane, the TeV brane, at a (few) TeV scale $ρ_T$, and a dark brane, at a (sub)-GeV scale $ρ_1\lesssim 100$ GeV $\llρ_T$. The Standard Model is localized in the TeV brane, thus solving the Higgs hierarchy problem, while the dark matter $χ$, a Dirac fermion with mass $m_χ<ρ_1$, is localized in the dark brane. The radion, with mass $m_r<m_χ$, interacts strongly ($\sim m_χ/ρ_1\sim\mathcal O(1)$) with dark matter and very weakly ($\sim m_{f}ρ_1/ρ_T^2\ll 1$) with the Standard Model matter $f$. The generic conflict between the bounds on its detection signatures and its proper relic abundance is avoided as dark matter annihilation is $p$-wave suppressed. The former is determined by its very weak interactions with the SM and the latter by its much stronger annihilation into radions. Therefore, there is a vast range in the Dark Matter's parameter space where the correct relic abundance is achieved consistently with the existing bounds. Moreover, for the dark brane with $ρ_1\lesssim 3$ GeV, a confinement/deconfinement first order phase transition, where the radion condensates, produces a stochastic gravitational waves background at the nanoHz frequencies, which can be identified with the signal detected by the Pulsar Timing Array (PTA) experiments. In the PTA window, for $0.15 \textrm{ GeV}\lesssim m_χ\lesssim 2$ GeV the relic abundance is reproduced and all constraints are satisfied.

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arXiv2024

Holographic Fluids from 5D Dilaton Gravity

We study a solvable class of five-dimensional dilaton gravity models that continuously interpolate between anti-de Sitter (AdS$_5$), linear dilaton (LD$_5$) and positively curved spacetimes as a function of a continuous parameter $ν$. The dilaton vacuum expectation value is set by a potential localized on a flat brane. We chart the elementary properties of these backgrounds for any admissible $ν$, and determine stability conditions of the brane-dilaton system. We find that the spectrum of metric fluctuations can be either continuous or discrete. It features a massless graviton mode confined between the brane and the curvature singularity, and a massive radion mode tied to brane-dilaton stability. We show that, in the presence of a bulk black hole, the holographic theory living on the brane features a perfect fluid. The equation of state of the holographic fluid interpolates between radiation, pressureless matter and vacuum energy as a function of $ν$. This extends earlier findings on holographic fluids. Our results suggest that the thermodynamics of the fluid mirrors precisely the thermodynamics of the bulk black hole.

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arXiv2024

Undecay

Unstable particles decay sooner or later, so they are not described by asymptotic one-particle states and they should not be included as independent states in unitarity relations such as the optical theorem. The same applies to any countable collection of unstable particles. We show that the behaviour of unparticle stuff, that is, a continuous collection of particles with different masses and common decay channels, is pretty different: it has a non-vanishing probability of surviving for ever and the corresponding asymptotic states must be taken into account to comply with unitarity. We also discuss compressed spectra and the transition from the discrete to the continuous case.

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arXiv2024

Holography of Linear Dilaton Spacetimes from the Bottom Up

The linear dilaton background is the keystone of a string-derived holographic correspondence beyond AdS$_{d+1}$/CFT$_d$. This motivates an exploration of the $(d+1)$-dimensional linear dilaton spacetime (LD$_{d+1}$) and its holographic properties from the low-energy viewpoint. We first notice that the LD$_{d+1}$ space has simple conformal symmetries, that we use to shape an effective field theory (EFT) on the LD background. We then place a brane in the background to study holography at the level of quantum fields and gravity. We find that the holographic correlators from the EFT feature a pattern of singularities at certain kinematic thresholds. We argue that such singularities can be used to bootstrap the putative $d$-dimensional dual theory using techniques analogous to those of the Cosmological Bootstrap program. Turning on finite temperature, we study the holographic fluid emerging on the brane in the presence of a bulk black hole. We find that the holographic fluid is pressureless for any $d$ due to a cancellation between Weyl curvature and dilaton stress tensor, and verify consistency with the time evolution of the theory. From the fluid thermodynamics, we find a universal temperature and Hagedorn behavior for any $d$. This matches the properties of a CFT$_2$ with large $T\overline T$ deformation, and of little string theory for $d=6$. Both the fluid equation of state and the spectrum of quantum fluctuations suggest that the $d$-dimensional dual theory arising from LD$_{d+1}$ is generically gapped.

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arXiv2024

Drell-Yan Bounds on Gapped Continuum Spectra

Theories with gapped continuum spectra have gotten some attention, either as pure 4D models like unparticles, or in 5D realizations as certain soft walls constructions. In this paper, we derive experimental bounds from Drell-Yan processes ($pp \to \ell^+\ell^-$, $pp \to \ell^\pm ν$) in a particular scenario where the electroweak bosons propagate in an extra dimension that produces a propagator with a continuum spectrum, on top of the isolated corresponding Standard Model pole. Using current LHC data we put a lower bound on the gap of 4.2 TeV (expected), 6.2 TeV (observed, bins with $< 10$ events combined) at 95\% CL, with some dependence in the observed limit on how low statistics bins are treated. We also study the limits for HL-LHC.

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arXiv2023

Pulsar Timing Array Stochastic Background from light Kaluza-Klein resonances

We investigate the potential of the warped-extradimension framework as an explanation for the recently observed stochastic gravitational background at nHz frequencies in pulsar timing arrays (PTA). Our analysis reveals that the PTA data can be effectively accommodated by a first-order phase transition triggered by a radion at the MeV-GeV scale feebly coupled to the Standard Model. Remarkably, this outcome remains robust irrespective of the specific details of the warped extradimension embedding, providing a foundation for future investigations aiming to develop concrete extradimension descriptions of Nature. We also demonstrate that many existing embeddings are not viable, as their radion and graviton phenomenology clash with a MeV-GeV scale radion. As a possible way-out, we sketch a promising solution involving multiple branes, wherein the light radion, graviton, and ensuing light resonances remain consistent with collider bounds and gravity tests.

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arXiv2023

Cosmological Dark Matter from a Bulk Black Hole

We study the cosmology of a three-brane in a specific five-dimensional scalar-gravity (i.e. soft-wall) background, known as the linear dilaton background. We discover that the Friedmann equation of the brane-world automatically contains a term mimicking pressureless matter. We propose to identify this term as dark matter. This dark matter arises as a projection of the bulk black hole on the brane, which contributes to the brane Friedmann equation via both the Weyl tensor and the scalar stress tensor. The nontrivial matter-like behavior is due to an exact cancellation between the Weyl and scalar pressures. We show that the Newtonian potential only receives a mild short-distance correction going as inverse distance squared, ensuring compatibility of the linear dilaton brane-world with observed 4D gravity. Our setup can be viewed as a consistent cosmological description of the holographic theories arising in the linear dilaton background. We also present more general scalar-gravity models where the brane cosmology features an effective energy density whose behavior smoothly interpolates between dark radiation, dark matter and dark energy depending on a model parameter.

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