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Journal articleEtkin A, Magueijo J, Rassouli FS, 2024,
Vortices, topology and time
, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 855, ISSN: 03702693We 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 onshell becomes fourvolume time. If the theory is restricted to a topological axionic form (viz. a parityodd product of an electric and a magnetic field), such a time variable becomes the spatial integral of the ChernSimons 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. Nonabelian extensions, and targetting parameters other than Λ are briefly examined, exposing different types of vortices and a possible role for interlinking leading to new phenomenology.

Journal articleHull C, Hutt ML, Lindström U, 2024,
Charges and topology in linearised gravity
, Journal of High Energy Physics, Vol: 2024Covariant conserved 2form currents for linearised gravity are constructed by contracting the linearised curvature with conformal KillingYano 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 offshell 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 welldefined 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 gaugeinvariant 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 KaluzaKlein compactifications and check our results in a number of examples.

Journal articleMagueijo J, 2024,
Dark matter and spacetime symmetry restoration
, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 109, ISSN: 15502368We 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 spacetime 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 “paintedon” 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 articleGerhardinger M, Giblin JT, Tolley AJ, et al., 2024,
Simulating a numerical UV completion of quartic Galileons
, Physical Review D, Vol: 109, ISSN: 24700010The 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 lowpass 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 lowenergy behavior. Here we show how the numerical UVcompletion 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.

Journal articleBasile T, Joung E, Mkrtchyan K, et al., 2024,
Spinorhelicity representations of particles of any mass in dS4 and AdS4 spacetimes
, Physical Review D, Vol: 109, ISSN: 24700010The spinorhelicity representations of massive and (partially) massless particles in fourdimensional (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 antide 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 spinorhelicity 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 spinorhelicity 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.

Journal articleCarrillo González M, de Rham C, Jaitly S, et al., 2024,
Positivitycausality competition: a road to ultimate EFT consistency constraints
, Journal of High Energy Physics, Vol: 2024Effective 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 nonlinear positivity bounds) and compare these constraints with the requirement of causal propagation of the photon modes around nontrivial 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.

Journal articleAbend S, Allard B, Alonso I, et al., 2024,
Terrestrial verylongbaseline atom interferometry: Workshop summary
, AVS Quantum Science, Vol: 6This document presents a summary of the 2023 Terrestrial VeryLongBaseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in largescale 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 protocollaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial largescale 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 mid2030s. 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.

Journal articleMentasti G, Contaldi CR, Peloso M, 2024,
Probing the galactic and extragalactic gravitational wave backgrounds with spacebased interferometers
, Journal of Cosmology and Astroparticle Physics, Vol: 2024, Pages: 055055<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 spacebased 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 timedependent 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 LISAonly 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 articleShi D, Shang F, Chen B, et al., 2024,
Local dominance unveils clusters in networks
, Communications Physics, Vol: 7, ISSN: 23993650Clusters or communities can provide a coarsegrained 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 inbetween, via concepts such as the cut, conductance, or modularity. Here we consider another perspective built on the notion of local dominance, where lowdegree nodes are assigned to the basin of influence of highdegree 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 groundtruth 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 articleHanany A, Kumaran G, Li C, et al., 2024,
Actions on the quiver: discrete quotients on the Coulomb branch
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 10298479 
Journal articleHull CM, 2024,
Magnetic charges for the graviton
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 10298479 
Conference paperTseytlin AA, 2024,
AdS/CFT, Wilson loops and M2branes
We discuss testing AdS/CFT correspondence between U(N)k × U(N)k ChernSimonsmatter 3d gauge theory and Mtheory 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.

Journal articleAlbertini E, Dowker F, Nasiri A, et al., 2024,
Inin correlators and scattering amplitudes on a causal set
, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 109, ISSN: 15502368Causal 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 largescale (lowenergy) 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 inin correlators in local scalar field theories with finite polynomial interactions. We outline how these same correlators can be computed using the doublepath integral, which acts as a generating functional for the inin correlators. We modify the inin generating functional to obtain a generating functional for inout correlators. We define a notion of scattering amplitudes on causal sets with noninteracting past and future regions and verify that they are given by 𝑆matrix elements (matrix elements of the timeevolution operator). We describe how these formal developments can be implemented to compute early Universe observables under the assumption that spacetime is fundamentally discrete.

Journal articlede Rham C, Giblin JT, Tolley AJ, 2024,
Scalar radiation with a quartic Galileon
, PHYSICAL REVIEW D, Vol: 109, ISSN: 24700010 
Journal articleLehners JL, Stelle KS, 2024,
Higherorder gravity, finite action, and a safe beginning for the universe
, EUROPEAN PHYSICAL JOURNAL PLUS, Vol: 139, ISSN: 21905444 
Journal articleColas 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: 2024We investigate quantum decoherence in a class of models which interpolates between expanding (inflation) and contracting (ekpyrosis) scenarios. For the cases which result in a scaleinvariant 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 latetime (secular growth) breakdown of perturbation theory often occurs in these cases. Instead, we establish a simple yet powerful latetime 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.

Journal articleGhoderao PS, Rajantie A, 2024,
Curvature perturbations from preheating with scale dependence
, Journal of Cosmology and Astroparticle Physics, Vol: 2024We extend the formalism to calculate nonGaussianity 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 nonperturbative 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 timedependence 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 observationallyviable preheating model motivated by nonminimal coupling to gravity, and study its full parameter dependence.

Journal articleMentasti G, Contaldi CR, 2024,
Observing gravitational waves with solar system astrometry
, Journal of Cosmology and Astroparticle Physics, Vol: 2024, ISSN: 14757516The 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 nonEinsteinian 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 articleGenolini PB, Gauntlett JP, Jiao Y, et al., 2024,
Localization and attraction
, The Journal of High Energy Physics, Vol: 2024, ISSN: 10298479We use equivariant localization to construct ofshell 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 ofshellexpression for the central charge of the dual N = (0, 2), d = 2 SCFT.

Journal articleFigueroa DG, Pieroni M, Ricciardone A, et al., 2024,
Cosmological Background Interpretation of Pulsar Timing Array Data.
, Phys Rev Lett, Vol: 132We discuss the interpretation of the detected signal by pulsar timing array (PTA) observations as a gravitational wave background of cosmological origin. We combine NANOGrav 15years and EPTADR2new datasets and confront them against backgrounds from supermassive black hole binaries (SMBHBs), and cosmological signals from inflation, cosmic (super)strings, firstorder phase transitions, Gaussian and nonGaussian large scalar fluctuations, and audible axions. We find that scalarinduced, 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 nonGaussianity at PTA scales as f_{nl}≲2.34 at 95% C.L.

Journal articleHull CM, 2024,
Covariant action for selfdual <i>p</i>form gauge fields in general spacetimes
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 10298479 
Journal articleIsichei 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: 11241861We study the Hamiltonian structure ofunimodularlike 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, thegaugefixed 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) zeromode receives modified dynamics. The implications are investigated, with the phenomenology dependingcrucially on the target “constant”.

Journal articleBeccaria 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: 05503213 
Journal articleSkrzypek T, Tseytlin AA, 2024,
On AdS/CFT duality in the twisted sector of string theory on <i>AdS</i><sub>5</sub> x <i>S</i><SUP>5</SUP><i>/</i>Z<sub>2</sub> orbifold background
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 10298479 
Journal articleHulik O, Malek E, Valach F, et al., 2024,
Yalgebroids and <i>E</i><sub>7(7)</sub> x R<SUP>+</SUP>generalised geometry
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 10298479 
Journal articleEvnin O, Joung E, Mkrtchyan K, 2024,
Democratic Lagrangians from topological bulk
, PHYSICAL REVIEW D, Vol: 109, ISSN: 24700010 
Journal articleKarapetyan M, Manvelyan R, Mkrtchyan K, 2024,
On correlation functions of higherspin currents in arbitrary dimensions d > 3
, Journal of High Energy Physics, Vol: 2024We revisit the problem of classification and explicit construction of the conformal threepoint correlation functions of currents of arbitrary integer spin in arbitrary dimensions. For the conserved currents, we set up the equations for the conservation conditions and solve them completely for some values of spins, confirming the earlier counting of the number of independent structures matching them with the higherspin cubic vertices in one higher dimension. The general solution for the correlators of conserved currents we delegate to a followup work.

Journal articleCable A, Rajantie A, 2024,
Stochastic parameters for scalar fields in de Sitter spacetime
, PHYSICAL REVIEW D, Vol: 109, ISSN: 24700010 
Journal articleMagueijo J, 2024,
Black holes and foliationdependent physics
, Physical Review D, Vol: 109, ISSN: 24700010In theories where physics depends on a global foliation of spacetime, a black hole’s horizon is surrounded by an “eternity skin”: a pileup of spacelike leaves that in the farout region cover all times from the start of collapse to future eternity. Any future foliationdependent change in the laws of physics would be enacted in this region and affect the last stages of collapse toward black hole formation. We show how in some cases the black hole never forms but, rather, bounces into an explosive event. There is also a nonlocal transfer of energy between the asymptotic Universe and the formed black hole precursor, so that the back hole (if formed) or the exploding star (otherwise) will have a different mass from what was initially thrown in. These last matters are generic to nonlocal theories and can be traced to the breakdown of the local Hamiltonian constraint.

Journal articleGenolini PB, Gauntlett JP, Sparks J, 2024,
Equivariant localization for AdS/CFT
, The Journal of High Energy Physics, Vol: 2024, ISSN: 10298479We explain how equivariant localization may be applied to AdS/CFT to compute various BPS observables in gravity, such as central charges and conformal dimensions of chiral primary operators, without solving the supergravity equations. The key ingredient is that supersymmetric AdS solutions with an Rsymmetry are equipped with a set of equivariantly closed forms. These may in turn be used to impose flux quantization and compute observables for supergravity solutions, using only topological information and the BerlineVergneAtiyahBott fixed point formula. We illustrate the formalism by considering AdS5 × M6 and AdS3 × M8 solutions of D = 11 supergravity. As well as recovering results for many classes of wellknown supergravity solutions, without using any knowledge of their explicit form, we also compute central charges for which explicit supergravity solutions have not been constructed.
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