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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
    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.
  • 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
    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.
  • 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.
  • 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
    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.
  • 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
  • Journal article
    Hull CM, 2024,

    Magnetic charges for the graviton

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • 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.
  • 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
    Genolini PB, Gauntlett JP, Jiao Y, Luescher A, Sparks Jet al., 2024,

    Localization and attraction

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    de Rham C, Giblin JT, Tolley AJ, 2024,

    Scalar radiation with a quartic Galileon

    , PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010
  • 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
  • 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.
  • 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.
  • 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
  • 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”.
  • 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
  • Journal article
    Skrzypek 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: 1029-8479
  • Journal article
    Hulik O, Malek E, Valach F, Waldram Det al., 2024,

    Y-algebroids and <i>E</i><sub>7(7)</sub> x R<SUP>+</SUP>-generalised geometry

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    Evnin O, Joung E, Mkrtchyan K, 2024,

    Democratic Lagrangians from topological bulk

    , PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010
  • Journal article
    Karapetyan M, Manvelyan R, Mkrtchyan K, 2024,

    On correlation functions of higher-spin currents in arbitrary dimensions d &gt; 3

    , Journal of High Energy Physics, Vol: 2024

    We revisit the problem of classification and explicit construction of the conformal three-point 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 higher-spin cubic vertices in one higher dimension. The general solution for the correlators of conserved currents we delegate to a follow-up work.
  • Journal article
    Cable A, Rajantie A, 2024,

    Stochastic parameters for scalar fields in de Sitter spacetime

    , PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010
  • Journal article
    Magueijo J, 2024,

    Black holes and foliation-dependent physics

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

    In theories where physics depends on a global foliation of space-time, a black hole’s horizon is surrounded by an “eternity skin”: a pile-up of spacelike leaves that in the far-out region cover all times from the start of collapse to future eternity. Any future foliation-dependent 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 article
    Genolini PB, Gauntlett JP, Sparks J, 2024,

    Equivariant localization for AdS/CFT

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

    We 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 R-symmetry 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 Berline-Vergne-Atiyah-Bott 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 well-known supergravity solutions, without using any knowledge of their explicit form, we also compute central charges for which explicit supergravity solutions have not been constructed.
  • Journal article
    Alexandre B, Gielen S, Magueijo J, 2024,

    Overall signature of the metric and the cosmological constant

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

    We consider a little known aspect of signature change, where the overall sign of the metric is allowed to change, with physical implications. We show how, in different formulations of general relativity, this type of classical signature change across boundaries with a degenerate metric can be made consistent with a change in sign (and value) of the cosmological constant Λ. In particular, the separate "mostly plus" and "mostly minus" signature sectors of Lorentzian gravity are most naturally associated with different signs of Λ. We show how this general phenomenon allows for classical solutions where the open dS patch can arise from a portion of AdS space time. These can be interpreted as classical "imaginary space" extensions of the usual Lorentzian theory, with a2 < 0.

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