Publications

Journal article

Hull C, Hutt ML, Lindström U, 2024,

Gauge-invariant magnetic charges in linearised gravity

, Classical and Quantum Gravity, Vol: 41, Pages: 195012-195012, ISSN: 0264-9381

<jats:title>Abstract</jats:title> <jats:p>Linearised gravity has magnetic charges carried by (linearised) Kaluza–Klein monopoles. A gauge-invariant expression is found for these charges that is similar to Penrose’s gauge-invariant expression for the ADM charges. A systematic search is made for other gauge-invariant charges.</jats:p>

Journal article

Viegas E, Evans T, 2024,

The Behavioural House Indicator: a faster and real time small-area indicative deprivation measure for England

, Environment and Planning B: Urban Analytics and City Science, ISSN: 2399-8083

Researchers have been long preoccupied with the measuring and monitoring of economic and social deprivation at small scales, neighbourhood, level in order to provide official government agencies and policy makers with more precise data insights. Whist valuable methodologies have been developed, the exercise of data collection associated with these methods tends to be expensive, time consuming, published infrequently with significant time delays, and subject to recurring changes to methodology. Here, we propose a novel method based on a straightforward methodology and data sources to generate a faster and real time indicator for deprivation at different scaling, small to larger areas. The results of our work show that our method provides a consistent view of deprivation across the regions of England and Wales, which are in line with the other indexes, but also highlight specific flash points of deep rural and highly dense urban deprivation areas that are not well captured by existing indexes. Our method is intended to aid researchers and policy makers by complementing existing but infrequent indexes.

Journal article

Babak S, Falxa M, Franciolini G, Pieroni Met al., 2024,

Forecasting the sensitivity of pulsar timing arrays to gravitational wave backgrounds

, Physical Review D, Vol: 110, ISSN: 2470-0010

<jats:p>Pulsar timing array (PTA) observations hinted towards the existence of a stochastic gravitational wave background (SGWB) in the nHz frequency band. Still, the nature of the SGWB signal cannot be confidently inferred from current data, and the leading explanation invokes mergers of supermassive black holes. If confirmed, such discovery would not only represent a turning point in our understanding of astrophysics, but it may severely limit the capability of searching for additional cosmological sources in the nHz frequency range. In this work, we build a simple framework to forecast the sensitivity of future pulsar timing array configurations and assess the parameter estimation of SGWB, which could consist of several contributions. We release the code , implementing this framework and ready to use.</jats:p> <jats:sec> <jats:title/> <jats:supplementary-material> <jats:permissions> <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement> <jats:copyright-year>2024</jats:copyright-year> </jats:permissions> </jats:supplementary-material> </jats:sec>

Journal article

Acharya B, Alexandre J, Behera SC, Benes P, Bergmann B, Bertolucci S, Bevan A, Brancaccio R, Branzas H, Burian P, Campbell M, Cecchini S, Cho YM, de Montigny M, De Roeck A, Ellis JR, Fairbairn M, Felea D, Frank M, Gould O, Hays J, Hirt AM, Ho DL-J, Hung PQ, Janecek J, Kalliokoski M, Lacarrère DH, Leroy C, Levi G, Margiotta A, Maselek R, Maulik A, Mauri N, Mavromatos NE, Millward L, Mitsou VA, Musumeci E, Ostrovskiy I, Ouimet P-P, Papavassiliou J, Patrizii L, Păvălaş GE, Pinfold JL, Popa LA, Popa V, Pozzato M, Pospisil S, Rajantie A, Ruiz de Austri R, Sahnoun Z, Sakellariadou M, Sakurai K, Sarkar S, Semenoff G, Shaa A, Sirri G, Sliwa K, Soluk R, Spurio M, Staelens M, Suk M, Tenti M, Togo V, Tuszyński JA, Upreti A, Vento V, Vives Oet al., 2024,

MoEDAL Search in the CMS Beam Pipe for Magnetic Monopoles Produced via the Schwinger Effect.

, Phys Rev Lett, Vol: 133

We report on a search for magnetic monopoles (MMs) produced in ultraperipheral Pb-Pb collisions during Run 1 of the LHC. The beam pipe surrounding the interaction region of the CMS experiment was exposed to 184.07 μb^{-1} of Pb-Pb collisions at 2.76 TeV center-of-mass energy per collision in December 2011, before being removed in 2013. It was scanned by the MoEDAL experiment using a SQUID magnetometer to search for trapped MMs. No MM signal was observed. The two distinctive features of this search are the use of a trapping volume very close to the collision point and ultrahigh magnetic fields generated during the heavy-ion run that could produce MMs via the Schwinger effect. These two advantages allowed setting the first reliable, world-leading mass limits on MMs with high magnetic charge. In particular, the established limits are the strongest available in the range between 2 and 45 Dirac units, excluding MMs with masses of up to 80 GeV at a 95% confidence level.

Journal article

Arav I, Gauntlett JP, Jiao Y, Roberts MM, Rosen Cet al., 2024,

Superconformal monodromy defects in N=4 SYM and LS theory

, Journal of High Energy Physics, Vol: 2024

We study type IIB supergravity solutions that are dual to two-dimensional superconformal defects in d = 4 SCFTs which preserve N = (0, 2) supersymmetry. We consider solutions dual to defects in N = 4 SYM theory that have non-trivial monodromy for U(1)3 ⊂ SO(6) global symmetry and we also allow for the possibility of conical singularities. In addition, we consider the addition of fermionic and bosonic mass terms that have non trivial dependence on the spatial directions transverse to the defect, while preserving the superconformal symmetry of the defect. We compute various physical quantities including the central charges of the defect expressed as a function of the monodromy, the on-shell action as well as associated supersymmetric Rényi entropies. Analogous computations are carried out for superconformal defects in the N = 1, d = 4 Leigh-Strassler SCFT. We also show that the defects of the two SCFTs are connected by a line of bulk marginal mass deformations and argue that they are also related by bulk RG flow.

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Journal article

Seibold FK, Tseytlin AA, 2024,

Scattering on the supermembrane

, Journal of High Energy Physics, Vol: 2024

We compute the one-loop 2 → 2 scattering amplitude of massless scalars on the world volume of an infinite D = 11 supermembrane quantized in the static gauge. The resulting expression is manifestly finite and turns out to be much simpler than in the bosonic membrane case in arXiv:2308.12189 being proportional to the tree-level scattering amplitude. We also consider the case of ℝ1, 1 × S1 membrane with one dimension compactified on a circle of radius R and demonstrate how the supermembrane scattering amplitude reduces to the one on an infinite D = 10 Green-Schwarz superstring in the limit of R→ 0.

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Journal article

Etkin A, Magueijo J, Rassouli F-S, 2024,

Vortices, topology and time

, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 855, ISSN: 0370-2693

We relate physical time with the topology of magnetic field vortices. We base ourselves on a formulation of unimodular gravity where the cosmological constant Λ appears as the canonical dual to a variable which on-shell becomes four-volume time. If the theory is restricted to a topological axionic form (viz. a parity-odd product of an electric and a magnetic field), such a time variable becomes the spatial integral of the Chern-Simons density. The latter equates to helicity, so that unimodular time is transmuted into the linking number of the vortices of the topological magnetic field, times their flux. With the added postulate that this flux is a universal constant, the flow of time can thus be interpreted as the progressive weaving of further links between magnetic field vortices, each link providing a quantum of time with value related to the fixed flux. Non-abelian extensions, and targetting parameters other than Λ are briefly examined, exposing different types of vortices and a possible role for inter-linking leading to new phenomenology.

Journal article

Hull C, Hutt ML, Lindström U, 2024,

Charges and topology in linearised gravity

, Journal of High Energy Physics, Vol: 2024

Covariant conserved 2-form currents for linearised gravity are constructed by contracting the linearised curvature with conformal Killing-Yano tensors. The corresponding conserved charges were originally introduced by Penrose and have recently been interpreted as the generators of generalised symmetries of the graviton. We introduce an off-shell refinement of these charges and find the relation between these improved Penrose charges and the linearised version of the ADM momentum and angular momentum. If the graviton field is globally well-defined on a background Minkowski space then some of the Penrose charges give the momentum and angular momentum while the remainder vanish. We consider the generalisation in which the graviton has Dirac string singularities or is defined locally in patches, in which case the conventional ADM expressions are not invariant under the graviton gauge symmetry in general. We modify them to render them gauge-invariant and show that the Penrose charges give these modified charges plus certain magnetic gravitational charges. We discuss properties of the Penrose charges, generalise to toroidal Kaluza-Klein compactifications and check our results in a number of examples.

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Citations: 1

Journal article

Jiang H, Tseytlin AA, 2024,

On co-dimension 2 defect anomalies in N = 4 SYM and (2,0) theory via brane probes in AdS/CFT

, Journal of High Energy Physics, Vol: 2024

We consider a 12-BPS solution for a D3 brane probe in AdS5× S5 that has world-volume geometry of AdS3× S1. It intersects the boundary over a surface that represents a dimension 2 defect in the boundary N = 4 SYM theory. The effective action of the probe brane is proportional to the logarithmically divergent volume of AdS3 and may thus be interpreted as computing conformal anomaly of supersymmetric S2 defect. The classical action scales as N. We compute the 1-loop correction to it due to quantum fluctuations of the D3 brane world-volume fields and compare the result to an earlier suggested expression for the defect anomaly. We also perform a similar analysis of a 12-BPS M5 brane probe solution in AdS7× S4 with the world-volume geometry of AdS5× S1 that represents a dimension 4 defect in the boundary (2,0) 6d theory. Here the classical M5 brane action computes the leading order N2 term in a-anomaly of the supersymmetric S4 defect. We perform a detailed computation of the 1-loop correction to the M5 brane effective action and thus provide a prediction for the subleading constant in the S4 defect a-anomaly coefficient.

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Journal article

Basile T, Joung E, Mkrtchyan K, Mojaza Met al., 2024,

Spinor-helicity representations of particles of any mass in dS4 and AdS4 spacetimes

, Physical Review D, Vol: 109, ISSN: 2470-0010

The spinor-helicity representations of massive and (partially) massless particles in four-dimensional (anti-)de Sitter (A)dS spacetime are studied within the framework of the dual pair correspondence. We show that the dual groups (also known as "little groups") of the anti-de Sitter and de Sitter groups are, respectively, O(2N) and O∗(2N). For N=1, the generator of the dual algebra so(2)≅so∗(2)≅u(1) corresponds to the helicity operator, and the spinor-helicity representation describes massless particles in (A)dS4. For N=2, the dual algebra is composed of two ideals, s and mΛ. The former ideal s≅so(3) fixes the spin of the particle, while the mass is determined by the latter ideal mΛ, which is isomorphic to so(2,1), iso(2), or so(3) depending on the cosmological constant being positive, zero, or negative. In the case of a positive cosmological constant, namely dS4, the spinor-helicity representation contains all massive particles corresponding to the principal series representations and the partially massless particles corresponding to the discrete series representations leaving out only the light massive particles corresponding to the complementary series representations. The zero and negative cosmological constant cases, which had been addressed in earlier references, are also discussed briefly. Finally, we consider the multilinear form of helicity spinors invariant under (A)dS group, which can serve as the (A)dS counterpart of the scattering amplitude, and discuss technical differences and difficulties of the (A)dS cases compared to the flat spacetime case.

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Journal article

Gerhardinger M, Giblin JT, Tolley AJ, Trodden Met al., 2024,

Simulating a numerical UV completion of quartic Galileons

, Physical Review D, Vol: 109, ISSN: 2470-0010

The Galileon theory is a prototypical effective field theory that incorporates the Vainshtein screening mechanism - a feature that arises in some extensions of general relativity, such as massive gravity. The Vainshtein effect requires that the theory contain higher order derivative interactions, which results in Galileons, and theories like them, failing to be technically well posed. While this is not a fundamental issue when the theory is correctly treated as an effective field theory, it nevertheless poses significant practical problems when numerically simulating this model. These problems can be tamed using a number of different approaches: introducing an active low-pass filter and/or constructing a UV completion at the level of the equations of motion, which controls the high momentum modes. These methods have been tested on cubic Galileon interactions, and have been shown to reproduce the correct low-energy behavior. Here we show how the numerical UV-completion method can be applied to quartic Galileon interactions, and present the first simulations of the quartic Galileon model using this technique. We demonstrate that our approach can probe physics in the regime of the effective field theory in which the quartic term dominates, while successfully reproducing the known results for cubic interactions.

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Journal article

Magueijo J, 2024,

Dark matter and spacetime symmetry restoration

, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 109, ISSN: 1550-2368

We examine local physics in the presence of global variables: variables associated with the whole of the spacelike surfaces of a foliation. These could be the (pseudo)constants of nature and their conjugate times, but our statements are more general. Interactions between the local and the global (for example, dependence of the local action on global times dual to constants) degrades full space-time diffeomorphism invariance down to spatial diffeomorphism invariance, and so an extra degree of freedom appears. When these presumably primordial global interactions switch off, the local action recovers full invariance and so the usual two gravitons, but a legacy matter component is left over, bearing the extra degree of freedom. Under the assumption that the preferred foliation is geodesic, this component behaves like dark matter, except that 3 of its 4 local degrees of freedom are frozen, forcing its rest frame to coincide with the preferred foliation. The nonfrozen degree of freedom (the number density of the effective fluid) is the survivor of the extra “graviton” present in the initial theory and keeps memory of all the past global interactions that took place in a given location in the preferred foliation. Such “painted-on” dark matter is best distinguished from the conventional one in situations where the preferred frame would be preposterous if all 4 degrees of freedom of dark matter were available. We provide one example: an outflowing halo of legacy matter with exact escape speed at each point and a very specific profile, surrounding a condensed structure made of normal matter.

Journal article

Abend S, Allard B, Alonso I, Antoniadis J, Araujo H, Arduini G, Arnold AS, Asano T, Augst N, Badurina L, Balaz A, Banks H, Barone M, Barsanti M, Bassi A, Battelier B, Baynham CFA, Beaufils Q, Belic A, Beniwal A, Bernabeu J, Bertinelli F, Bertoldi A, Biswas IA, Blas D, Boegel P, Bogojevic A, Bohm J, Bohringer S, Bongs K, Bouyer P, Brand C, Brimis A, Buchmueller O, Cacciapuoti L, Calatroni S, Canuel B, Caprini C, Caramete A, Caramete L, Carlesso M, Carlton J, Casariego M, Charmandaris V, Chen YA, Chiofalo ML, Cimbri A, Coleman J, Constantin FL, Contaldi CR, Cui Y, Ros ED, Davies G, Rosendo EDP, Deppner C, Derevianko A, de Rham C, De Roeck A, Derr D, Pumpo FD, Djordjevic GS, Dobrich B, Domokos P, Dornan P, Doser M, Drougakis G, Dunningham J, Duspayev A, Easo S, Eby J, Efremov M, Ekelof T, Elertas G, Ellis J, Evans D, Fadeev P, Fanì M, Fassi F, Fattori M, Fayet P, Felea D, Feng J, Friedrich A, Fuchs E, Gaaloul N, Gao D, Gardner S, Garraway B, Gauguet A, Gerlach S, Gersemann M, Gibson V, Giese E, Giudice GF, Glasbrenner EP, Gundo M, Haehnelt M, Hakulinen T, Hammerer K, Hanımeli ETet al., 2024,

Terrestrial very-long-baseline atom interferometry: Workshop summary

, AVS Quantum Science, Vol: 6

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more kilometer–scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions.

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Citations: 2

Journal article

Mentasti G, Contaldi CR, Peloso M, 2024,

Probing the galactic and extragalactic gravitational wave backgrounds with space-based interferometers

, Journal of Cosmology and Astroparticle Physics, Vol: 2024, Pages: 055-055

<jats:title>Abstract</jats:title> <jats:p>We employ the formalism developed in [1] and [2] to study the prospect of detecting an anisotropic Stochastic Gravitational Wave Background (SGWB) with the Laser Interferometer Space Antenna (LISA) alone, and combined with the proposed space-based interferometer Taiji. Previous analyses have been performed in the frequency domain only. Here, we study the detectability of the individual coefficients of the expansion of the SGWB in spherical harmonics, by taking into account the specific motion of the satellites. This requires the use of time-dependent response functions, which we include in our analysis to obtain an optimal estimate of the anisotropic signal. We focus on two applications. Firstly, the reconstruction of the anisotropic galactic signal without assuming any prior knowledge of its spatial distribution. We find that both LISA and LISA with Taiji cannot put tight constraints on the harmonic coefficients for realistic models of the galactic SGWB. We then focus on the discrimination between a galactic signal of known morphology but unknown overall amplitude and an isotropic extragalactic SGWB component of astrophysical origin. In this case, we find that the two surveys can confirm, at a confidence level ≳ 3<jats:italic>σ</jats:italic>, the existence of both the galactic and extragalactic background if both have amplitudes as predicted in standard models. We also find that, in the LISA-only case, the analysis in the frequency domain (under the assumption of a time average of data taken homogeneously across the year) provides a nearly identical determination of the two amplitudes as compared to the optimal analysis.</jats:p>

Journal article

Carrillo González M, de Rham C, Jaitly S, Pozsgay V, Tokareva Aet al., 2024,

Positivity-causality competition: a road to ultimate EFT consistency constraints

, Journal of High Energy Physics, Vol: 2024

Effective field theories (EFT) are strongly constrained by fundamental principles such as unitarity, locality, causality, and Lorentz invariance. In this paper, we consider the EFT of photons (or other U(1) gauge field) and compare different approaches to obtain bounds on its Wilson coefficients. We present an analytic derivation of the implications of unitarity (linear and non-linear positivity bounds) and compare these constraints with the requirement of causal propagation of the photon modes around non-trivial backgrounds generated by external sources. Within this setup, we find that the low energy causality condition can give complementary constraints to our analytic positivity bounds. In other words, simple analytic techniques can give strong constraints on the allowed region of the photon EFT parameters even when the positivity bounds are not numerically optimized.

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Citations: 1

Journal article

Shi D, Shang F, Chen B, Expert P, Lü L, Stanley HE, Lambiotte R, Evans TS, Li Ret al., 2024,

Local dominance unveils clusters in networks

, Communications Physics, Vol: 7, ISSN: 2399-3650

Clusters or communities can provide a coarse-grained description of complex systems at multiple scales, but their detection remains challenging in practice. Community detection methods often define communities as dense subgraphs, or subgraphs with few connections in-between, via concepts such as the cut, conductance, or modularity. Here we consider another perspective built on the notion of local dominance, where low-degree nodes are assigned to the basin of influence of high-degree nodes, and design an efficient algorithm based on local information. Local dominance gives rises to community centers, and uncovers local hierarchies in the network. Community centers have a larger degree than their neighbors and are sufficiently distant from other centers. The strength of our framework is demonstrated on synthesized and empirical networks with ground-truth community labels. The notion of local dominance and the associated asymmetric relations between nodes are not restricted to community detection, and can be utilised in clustering problems, as we illustrate on networks derived from vector data.

Journal article

Hanany A, Kumaran G, Li C, Liu D, Sperling Met al., 2024,

Actions on the quiver: discrete quotients on the Coulomb branch

, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479

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Journal article

Hull CM, 2024,

Magnetic charges for the graviton

, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479

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Conference paper

Tseytlin AA, 2024,

AdS/CFT, Wilson loops and M2-branes

We discuss testing AdS/CFT correspondence between U(N)k × U(N)-k Chern-Simons-matter 3d gauge theory and M-theory in AdS4 × S7/Zk background. We show that the quantum M2 brane partition function expanded near the corresponding classical solution matches the localization predictions on the gauge theory side in the case of BPS Wilson loop expectation value and instanton corrections to free energy.

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Journal article

Albertini E, Dowker F, Nasiri A, Zalel Set al., 2024,

In-in correlators and scattering amplitudes on a causal set

, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 109, ISSN: 1550-2368

Causal set theory is an approach to quantum gravity in which spacetime is fundamentally discrete at the Planck scale and takes the form of an irregular Lorentzian lattice, or “causal set,” from which continuum spacetime emerges in a large-scale (low-energy) approximation. In this work, we present new developments in the framework of interacting quantum field theory on causal sets. We derive a diagrammatic expansion for in-in correlators in local scalar field theories with finite polynomial interactions. We outline how these same correlators can be computed using the double-path integral, which acts as a generating functional for the in-in correlators. We modify the in-in generating functional to obtain a generating functional for in-out correlators. We define a notion of scattering amplitudes on causal sets with noninteracting past and future regions and verify that they are given by 𝑆-matrix elements (matrix elements of the time-evolution operator). We describe how these formal developments can be implemented to compute early Universe observables under the assumption that spacetime is fundamentally discrete.

Journal article

de Rham C, Giblin JT, Tolley AJ, 2024,

Scalar radiation with a quartic Galileon

, PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010

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Journal article

Lehners J-L, Stelle KS, 2024,

Higher-order gravity, finite action, and a safe beginning for the universe

, EUROPEAN PHYSICAL JOURNAL PLUS, Vol: 139, ISSN: 2190-5444

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Journal article

Ghoderao PS, Rajantie A, 2024,

Curvature perturbations from preheating with scale dependence

, Journal of Cosmology and Astroparticle Physics, Vol: 2024

We extend the formalism to calculate non-Gaussianity of primordial curvature perturbations produced by preheating in the presence of a light scalar field. The calculation is carried out in the separate universe approximation using the non-perturbative delta N formalism and lattice field theory simulations. Initial conditions for simulations are drawn from a statistical ensemble determined by modes that left the horizon during inflation, with the time-dependence of Hubble rate during inflation taken into account. Our results show that cosmic variance, i.e., the contribution from modes with wavelength longer than the size of the observable universe today, plays a key role in determining the dominant contribution. We illustrate our formalism by applying it to an observationally-viable preheating model motivated by non-minimal coupling to gravity, and study its full parameter dependence.

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Journal article

Colas T, de Rham C, Kaplanek G, 2024,

Decoherence out of fire: purity loss in expanding and contracting universes

, Journal of Cosmology and Astroparticle Physics, Vol: 2024

We investigate quantum decoherence in a class of models which interpolates between expanding (inflation) and contracting (ekpyrosis) scenarios. For the cases which result in a scale-invariant power spectrum, we find that ekpyrotic universes lead to complete decoherence of the curvature perturbation before the bounce. This is in stark contrast to the inflationary case, where recoherence has been previously observed in some situations. Although the purity can be computed for couplings of all sizes, we also study the purity perturbatively and observe that late-time (secular growth) breakdown of perturbation theory often occurs in these cases. Instead, we establish a simple yet powerful late-time purity resummation which captures the exact evolution to a remarkable level, while maintaining analytical control. We conclude that the cosmological background plays a crucial role in the decoupling of the heavy fields during inflation and alternatives.

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Journal article

Genolini PB, Gauntlett JP, Jiao Y, Luescher A, Sparks Jet al., 2024,

Localization and attraction

, The Journal of High Energy Physics, Vol: 2024, ISSN: 1029-8479

We use equivariant localization to construct of-shell entropy functions for supersymmetric black holes in N = 2, D = 4 gauged supergravity coupled to matter. This allowsone to compute the black hole entropy without solving the supergravity equations of motionand provides a novel generalization of the attractor mechanism. We consider magneticallycharged black holes in AdS4 which have an AdS2 × M2 near horizon geometry, where M2 isa sphere or a spindle, and we also obtain entropy functions for ungauged supergravity as asimple corollary. We derive analogous results for black strings and rings in D = 5 supergravitywhich have an AdS3 × M2 near horizon geometry, and in this setting we derive an of-shellexpression for the central charge of the dual N = (0, 2), d = 2 SCFT.

Journal article

Mentasti G, Contaldi CR, 2024,

Observing gravitational waves with solar system astrometry

, Journal of Cosmology and Astroparticle Physics, Vol: 2024, ISSN: 1475-7516

The subtle influence of gravitational waves on the apparent positioning of celestial bodies offers novel observational windows [1,2,3,4]. We calculate the expected astrometric signal induced by an isotropic Stochastic Gravitational Wave Background (SGWB) in the short distance limit. Our focus is on the resultant proper motion of Solar System objects, a signal on the same time scales addressed by Pulsar Timing Arrays (PTA). We derive the corresponding astrometric deflection patterns, finding that they manifest as distinctive dipole and quadrupole correlations or, in some cases, may not be present. Our analysis encompasses both Einsteinian and non-Einsteinian polarisations. We estimate the upper limits for the amplitude of SGWBs that could be obtained by tracking the proper motions of large numbers of solar system objects such as asteroids. We find that for SGWBs with negative spectral indices, such as that generated by Super Massive Black Hole Binaries (SMBHB), the constraints from these observations could rival those from PTAs. With the Gaia satellite and the Vera C. Rubin Observatory poised to track an extensive sample of asteroids — ranging from Script O(105) to Script O(106), we highlight the significant future potential for similar surveys to contribute to our understanding of the SGWB.

Journal article

Figueroa DG, Pieroni M, Ricciardone A, Simakachorn Pet al., 2024,

Cosmological Background Interpretation of Pulsar Timing Array Data.

, Phys Rev Lett, Vol: 132

We discuss the interpretation of the detected signal by pulsar timing array (PTA) observations as a gravitational wave background of cosmological origin. We combine NANOGrav 15-years and EPTA-DR2new datasets and confront them against backgrounds from supermassive black hole binaries (SMBHBs), and cosmological signals from inflation, cosmic (super)strings, first-order phase transitions, Gaussian and non-Gaussian large scalar fluctuations, and audible axions. We find that scalar-induced, and to a lesser extent audible axion and cosmic superstring signals, provide a better fit than SMBHBs. These results depend, however, on modeling assumptions, so further data and analysis are needed to reach robust conclusions. Independently of the signal origin, the data strongly constrain the parameter space of cosmological signals, for example, setting an upper bound on primordial non-Gaussianity at PTA scales as |f_{nl}|≲2.34 at 95% C.L.

Journal article

Hull CM, 2024,

Covariant action for self-dual <i>p</i>-form gauge fields in general spacetimes

, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479

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Journal article

Beccaria M, Tseytlin AA, 2024,

Large N expansion of superconformal index of k=1 ABJM theory and semiclassical M5 brane partition function

, NUCLEAR PHYSICS B, Vol: 1001, ISSN: 0550-3213

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Journal article

Isichei R, Magueijo J, 2024,

Unimodular proca theory: breaking the U(1) gauge symmetry of unimodular gravity via a mass term

, European Physical Journal C: Particles and Fields, Vol: 84, ISSN: 1124-1861

We study the Hamiltonian structure ofunimodular-like theories, where the cosmological constant(or other supposed constants of nature) are demoted fromfixed parameters to classical constants of motion. No newlocal degrees of freedom are present as a result of a U(1)gauge invariance of the theory. Hamiltonian analysis of theaction reveals that the only possible gauge fixing that canbe enforced is setting the spatial components of the fourvolume time vector T i ≈ 0. As a consequence of this, thegauge-fixed unimodular path integral is equivalent to the minisuperspace unimodular path integral. However, should webreak the U(1) gauge invariance, two things happen: a massless propagating degree of freedom appears, and the (gaugeinvariant) zero-mode receives modified dynamics. The implications are investigated, with the phenomenology dependingcrucially on the target “constant”.

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AdS/CFT, Wilson loops and M2-branes

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