Results
- Showing results for:
- Reset all filters
Search results
-
Journal articleBasile T, Joung E, Mkrtchyan K, et al., 2024,
Spinor-helicity representations of particles of any mass in dS 4 and AdS 4 spacetimes
, PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010 -
Journal articleMentasti 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, ISSN: 1475-7516We 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 ≳ 3σ, 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.
-
Journal articleAbend S, Allard B, Alonso I, et al., 2024,
Terrestrial very-long-baseline atom interferometry: workshop summary
, AVS Quantum Science, Vol: 6, ISSN: 2639-0213This 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 articleShi D, Shang F, Chen B, et al., 2024,
Local dominance unveils clusters in networks
, Communications Physics, Vol: 7, ISSN: 2399-3650Clusters 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 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: 1029-8479 -
Journal articleHull CM, 2024,
Magnetic charges for the graviton
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479 -
Conference paperTseytlin 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 articleAlbertini E, Dowker F, Nasiri A, et al., 2024,
In-in correlators and scattering amplitudes on a causal set
, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 109, ISSN: 1550-2368Causal 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 articlede Rham C, Giblin JT, Tolley AJ, 2024,
Scalar radiation with a quartic Galileon
, PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010 -
Journal articleMentasti G, Contaldi CR, 2024,
Observing gravitational waves with solar system astrometry
, Journal of Cosmology and Astroparticle Physics, Vol: 2024, ISSN: 1475-7516The 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 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, ISSN: 1475-7516 -
Journal articleLehners J-L, Stelle KS, 2024,
Higher-order gravity, finite action, and a safe beginning for the universe
, European Physical Journal Plus, Vol: 139, ISSN: 2190-5444General relativity allows for inhomogeneous and anisotropic universes with finite action. By contrast, in quadratic gravity such solutions obtain infinite action and are thus eliminated. What remains are homogeneous and isotropic solutions undergoing accelerated expansion, thereby automatically inducing an early inflationary phase. In this manner, semi-classical consistency may explain some of the basic, coarse-grained features of the early universe. This includes suitable initial conditions for the second law of thermodynamics, in the spirit of the Weyl curvature hypothesis. We note that quadratic gravity is a renormalisable theory and may admit an asymptotically safe regime at high energies, rendering the theory trustworthy to high energies. We also comment on theories containing curvature terms up to infinite derivative order, and on the contrast with no-boundary initial conditions.
-
Journal articleGenolini PB, Gauntlett JP, Jiao Y, et al., 2024,
Localization and attraction
, The Journal of High Energy Physics, Vol: 2024, ISSN: 1029-8479We 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 articleGhoderao PS, Rajantie A, 2024,
Curvature perturbations from preheating with scale dependence
, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516 -
Journal articleFigueroa DG, Pieroni M, Ricciardone A, et al., 2024,
Cosmological Background Interpretation of Pulsar Timing Array Data
, PHYSICAL REVIEW LETTERS, Vol: 132, ISSN: 0031-9007 -
Journal articleCarrillo González M, 2024,
Bounds on EFT’s in an expanding universe
, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 109, ISSN: 1550-2368We find bounds on the Wilson coefficients of effective field theories (EFTs) living in a universe undergoing expansion by requiring that its modes do not propagate further than a minimally coupled photon by a resolvable amount. To do so, we compute the spatial shift suffered by the EFT modes at a fixed time slice within the WKB approximation and the regime of validity of the EFT. We analyze the bounds arising on shift-symmetric scalars and curved space generalizations of Galileons.
-
Journal articleHull 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 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: 1124-1861We 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 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: 0550-3213 -
Journal articleKarapetyan M, Manvelyan R, Mkrtchyan K, 2024,
On correlation functions of higher-spin currents in arbitrary dimensions <i>d</i> > 3
, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479 -
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: 1029-8479 -
Journal articleHulik O, Malek E, Valach F, et 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 articleEvnin O, Joung E, Mkrtchyan K, 2024,
Democratic Lagrangians from topological bulk
, PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010 -
Journal articleCable A, Rajantie A, 2024,
Stochastic parameters for scalar fields in de Sitter spacetime
, PHYSICAL REVIEW D, Vol: 109, ISSN: 2470-0010 -
Journal articleMagueijo J, 2024,
Black holes and foliation-dependent physics
, Physical Review D, Vol: 109, ISSN: 2470-0010In 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 articleGenolini PB, Gauntlett JP, Sparks J, 2024,
Equivariant localization for AdS/CFT
, The Journal of High Energy Physics, Vol: 2024, ISSN: 1029-8479We 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 articleAlexandre B, Gielen S, Magueijo J, 2024,
Overall signature of the metric and the cosmological constant
, Journal of Cosmology and Astroparticle Physics, Vol: 2024, ISSN: 1475-7516We 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.
-
Journal articleRoberts MM, Wiseman T, 2024,
Analog gravity and continuum effective theory of the graphene tight-binding lattice model
, PHYSICAL REVIEW B, Vol: 109, ISSN: 2469-9950 -
Journal articleHo M, Price HCW, Evans TS, et al., 2024,
Dynamics of technology emergence in innovation networks
, Scientific Reports, Vol: 14, ISSN: 2045-2322To create the next innovative product, participants in science need to understand which existing technologies can be combined, what new science must be discovered, and what new technologies must be invented. Knowledge of these often arrives by means of expert consensus or popularity metrics, masking key information on how intellectual efforts accumulate into technological progress. To address this shortcoming, we first present a method to establish a mathematical link between technological evolution and complex networks: a path of events that narrates innovation bottlenecks. Next, we quantify the position and proximity of documents to these innovation paths. The result is an innovation network that more exhaustively captures deterministic knowledge flows with respect to a marketed innovative product. Our dataset, containing over three million biomedical citations, demonstrates the possibility of quantifying the accumulation, speed, and division of labour in innovation over a sixty-year time horizon. The significance of this study includes the (i) use of a purpose-generated dataset showing causal paths from research to development to product; (ii) analysis of the innovation process as a directed acyclic graph; (iii) comparison between calendar time and network time; (iv) ordering of science funders along technology lifecycles; (v) quantification of innovative activities' importance to an innovative outcome; and (vi) integration of publication, patent, clinical trial, regulatory data to study innovation holistically.
-
Journal articleBassani PM, Magueijo J, 2024,
Unimodular-like times, evolution and Brans–Dicke gravity
, International Journal of Modern Physics D: Gravitation, Astrophysics and Cosmology, Vol: 33, ISSN: 0218-2718In unimodular-like theories, the constants of nature are demoted from pre-given parameters to phase space variables. Their canonical duals provide physical time variables. We investigate how this interacts with an alternative approach to varying constants, where they are replaced by dynamical scalar fields. Specifically, we investigate the Brans–Dicke theory of gravity and its interaction with clocks dual to the cosmological constant, the Planck mass, etc. We crucially distinguish between the different role of Newton’s G in this process, leading to the possibility of local Lorentz invariance violation. A large number of possible theories emerge, for example where the Brans–Dicke coupling, ω, depends on unimodular-like times (in a generalization of scalar-tensor theories), or even become the dual variable to unimodular-like clocks ticking variations in other demoted constants, such as the cosmological constant. We scan the space of possible theories and select those most interesting regarding the joint variations of the Brans–Dicke ω and other parameters, (such as the cosmological constant); and also regarding their energy conservation violation properties. This ground work is meant to provide the formalism for further developments, namely regarding cosmology, black holes and the cosmological constant problem.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.
Note to staff: Adding new publications to a research group
- Log in to Symplectic.
- Click on Menu > Create Links
- Choose what you want to create links between – in this case ‘Publications’ and ‘Organisational structures’.
- Choose the organisational structure (research group) into which you want to link the publications and check the box next to it.
- Now check the box of any publication you want to add to that group. You can use the filters to find what you want and select multiple publications if necessary.
- Scroll to the bottom and click the blue ‘Create new link’ button to link them.
- The publications will be added to the group, and will be displayed on the group publications feed within 24 hours (it is not immediate).
Any problems, talk to Tim Evans or the Faculty Web Team.