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  • Working paper
    Arav I, Cheung KCM, Gauntlett JP, Roberts MM, Rosen Cet al., 2020,

    Spatially modulated and supersymmetric mass deformations of N=4 SYM

    , Publisher: arXiv

    We study mass deformations of $\mathcal{N}=4$, $d=4$ SYM theory that arespatially modulated in one spatial dimension and preserve some residualsupersymmetry. We focus on generalisations of $\mathcal{N}=1^*$ theories andshow that it is also possible, for suitably chosen supersymmetric masses, topreserve $d=3$ conformal symmetry associated with a co-dimension one interface.Holographic solutions can be constructed using $D=5$ theories of gravity thatarise from consistent truncations of $SO(6)$ gauged supergravity and hence typeIIB supergravity. For the mass deformations that preserve $d=3$ superconformalsymmetry we construct a rich set of Janus solutions of $\mathcal{N}=4$ SYMtheory which have the same coupling constant on either side of the interface.Limiting classes of these solutions give rise to RG interface solutions with$\mathcal{N}=4$ SYM on one side of the interface and the Leigh-Strassler (LS)SCFT on the other, and also to a Janus solution for the LS theory. Anotherlimiting solution is a new supersymmetric $AdS_4\times S^1\times S^5$ solutionof type IIB supergravity.
  • Journal article
    Ashmore A, Strickland-Constable C, Tennyson D, Waldram Det al., 2020,

    Heterotic backgrounds via generalised geometry: moment maps and moduli

    , The Journal of High Energy Physics, Vol: 2020, Pages: 1-46, ISSN: 1029-8479

    We describe the geometry of generic heterotic backgrounds preserving minimal supersymmetry in four dimensions using the language of generalised geometry. They are characterised by an SU(3) × Spin(6 + n) structure within O(6, 6 + n) × ℝ+ generalised geometry. Supersymmetry of the background is encoded in the existence of an involutive subbundle of the generalised tangent bundle and the vanishing of a moment map for the action of diffeomorphisms and gauge symmetries. We give both the superpotential and the Kähler potential for a generic background, showing that the latter defines a natural Hitchin functional for heterotic geometries. Intriguingly, this formulation suggests new connections to geometric invariant theory and an extended notion of stability. Finally we show that the analysis of infinitesimal deformations of these geometric structures naturally reproduces the known cohomologies that count the massless moduli of supersymmetric heterotic backgrounds.
  • Journal article
    Catterall S, Giedt J, Jha RG, Schaich D, Wiseman Tet al., 2020,

    Three-dimensional super-Yang-Mills theory on the lattice and dual black branes

    , PHYSICAL REVIEW D, Vol: 102, ISSN: 2470-0010
  • Journal article
    Hoare B, Levine N, Tseytlin AA, 2020,

    Sigma models with local couplings: a new integrability-RG flow connection

    , The Journal of High Energy Physics, Vol: 20, ISSN: 1029-8479

    We consider several classes of σ-models (on groups and symmetric spaces, η-models, ⋋-models) with local couplings that may depend on the 2d coordinates, e.g. on time τ . We observe that (i) starting with a classically integrable 2d σ-model, (ii) formally promoting its couplings hα to functions hα(τ ) of 2d time, and (iii) demanding that the resulting time-dependent model also admits a Lax connection implies that hα(τ ) must solve the 1-loop RG equations of the original theory with τ interpreted as RG time. This provides a novel example of an ‘integrability-RG flow’ connection. The existence of a Lax connection suggests that these time-dependent σ-models may themselves be understood as integrable. We investigate this question by studying the possibility of constructing non-local and local conserved charges. Such σ-models with D-dimensional target space and time-dependent couplings subject to the RG flow naturally appear in string theory upon fixing the light-cone gauge in a (D + 2)-dimensional conformal σ-model with a metric admitting a covariantly constant null Killing vector and a dilaton linear in the null coordinate.
  • Journal article
    Chester SM, Green MB, Pufu SS, Wang Y, Wen Cet al., 2020,

    Modular invariance in superstring theory from $$ \mathcal{N} $$ = 4 super-Yang-Mills

    , Journal of High Energy Physics, Vol: 2020

    <jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>We study the four-point function of the lowest-lying half-BPS operators in the <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \mathcal{N} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>N</mml:mi> </mml:math></jats:alternatives></jats:inline-formula> = 4 SU(<jats:italic>N</jats:italic>) super-Yang-Mills theory and its relation to the flat-space four-graviton amplitude in type IIB superstring theory. We work in a large-<jats:italic>N</jats:italic> expansion in which the complexified Yang-Mills coupling <jats:italic>τ</jats:italic> is fixed. In this expansion, non-perturbative instanton contributions are present, and the SL(2<jats:italic>,</jats:italic> ℤ) duality invariance of correlation functions is manifest. Our results are based on a detailed analysis of the sphere partition function of the mass-deformed SYM theory, which was previously computed using supersymmetric localization. This partition function determines a certain integrated correlator in the undeformed <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \mathcal{N} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>N</mml:mi> </mml:math></jats:alternatives></jats:inline-formula> = 4 SYM theory, which in turn constrains the four-point correlator at separated points. In a normalization where the two-point functions are proportional to <jats:italic>N</jats:italic><jats:sup>2</jats:sup><jats:italic>−</jats:italic> 1 and are independent of <jats:italic>τ</jats:italic> and <jats:inline-formula><jat
  • Working paper
    Arav I, Cheung KCM, Gauntlett JP, Roberts MM, Rosen Cet al., 2020,

    Superconformal RG interfaces in holography

    , Publisher: arXiv

    We construct gravitational solutions that holographically describe twodifferent $d=4$ SCFTs joined together at a co-dimension one, planar RGinterface and preserving $d=3$ superconformal symmetry. The RG interface joins$\mathcal{N}=4$ SYM theory on one side with the $\mathcal{N}=1$ Leigh-StrasslerSCFT on the other. We construct a family of such solutions, which in generalare associated with spatially dependent mass deformations on the$\mathcal{N}=4$ SYM side, but there is a particular solution for which thesedeformations vanish. We also construct a Janus solution with theLeigh-Strassler SCFT on either side of the interface. Gravitational solutionsassociated with superconformal interfaces involving ABJM theory and two $d=3$$\mathcal{N}=1$ SCFTs with $G_2$ symmetry are also discussed and shown to havesimilar properties, but they also exhibit some new features.
  • Journal article
    de Rham C, Tolley AJ, 2020,

    Causality in curved spacetimes: The speed of light and gravity

    , PHYSICAL REVIEW D, Vol: 102, Pages: 1-33, ISSN: 1550-7998

    Within the low-energy effective field theories of quantum electrodynamics and gravity, the low-energy speed of light or that of gravitational waves can typically be mildly superluminal in curved spacetimes. Related to this, small scattering time advances relative to the curved background can emerge from known effective field theory coefficients for photons or gravitons. We clarify why these results are not in contradiction with causality, analyticity or Lorentz invariance, and highlight various subtleties that arise when dealing with superluminalities and time advances in the gravitational context. Consistent low-energy effective theories are shown to self-protect by ensuring that any time advance and superluminality calculated within the regime of validity of the effective theory is necessarily unresolvable, and cannot be argued to lead to a macroscopically larger light cone. Such considerations are particularly relevant for putting constraints on cosmological and gravitational effective field theories and we provide explicit criteria to be satisfied so as to ensure causality.
  • Journal article
    Giombi S, Tseytlin AA, 2020,

    Strong coupling expansion of circular Wilson loops and string theories in AdS5 x S^5 and AdS4 x CP^3

    , The Journal of High Energy Physics, Vol: 2020, Pages: 1-27, ISSN: 1029-8479

    We revisit the problem of matching the strong coupling expansion of the$\frac{1}{2}$ BPS circular Wilson loops in ${\cal N}=4$ SYM and ABJM gaugetheories with their string theory duals in ${\rm AdS}_5 \times S^5$ and ${\rmAdS}_4 \times CP^3$, at the first subleading (one-loop) order of the expansionaround the minimal surface. We observe that, including the overall factor$1/g_{\rm s}$ of the inverse string coupling constant, as appropriate for theopen string partition function with disk topology, and a universal prefactorproportional to the square root of the string tension $T$, both the SYM andABJM results precisely match the string theory prediction. We provide anexplanation of the origin of the $\sqrt T$ prefactor based on special featuresof the combination of one-loop determinants appearing in the string partitionfunction. The latter also implies a natural generalization $Z_\chi \sim (\sqrtT/g_{\rm s})^\chi$ to higher genus contributions with the Euler number $\chi$,which is consistent with the structure of the $1/N$ corrections found on thegauge theory side.
  • Journal article
    Hilton B, Sood AP, Evans TS, 2020,

    Predictive limitations of spatial interaction models: a non-Gaussian analysis

    , Scientific Reports, ISSN: 2045-2322

    We present a method to compare spatial interaction models against data basedon well known statistical measures which are appropriate for such models anddata. We illustrate our approach using a widely used example: commuting data,specifically from the US Census 2000. We find that the radiation model performssignificantly worse than an appropriately chosen simple gravity model. Variousconclusions are made regarding the development and use of spatial interactionmodels, including: that spatial interaction models fit badly to data in anabsolute sense, that therefore the risk of over-fitting is small and addingadditional fitted parameters improves the predictive power of models, and thatappropriate choices of input data can improve model fit.
  • Journal article
    Lee D-S, Lin C-Y, Rivers RJ, 2020,

    Large phonon time-of-flight fluctuations in expanding flat condensates of cold Fermi gases

    , JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 32, ISSN: 0953-8984
  • Journal article
    Fischetti S, Wallis L, Wiseman T, 2020,

    Does the round sphere maximize the free energy of (2+1)-dimensional QFTs?

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    de Rham C, Pozsgay V, 2020,

    New class of Proca interactions

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 1-18, ISSN: 1550-2368

    We propose a new class of Proca interactions that enjoy a nontrivial constraint and hence propagates the correct number of degrees of freedom for a healthy massive spin-1 field. We show that the scattering amplitudes always differ from those of the Generalized Proca. This implies that the new class of interactions proposed here are genuinely different from the Generalized Proca and there can be no local field redefinitions between the two. In curved spacetime, massive gravity is the natural covariantization, but we show how other classes of covariantizations can be considered.
  • Journal article
    Margalit A, Contaldi CR, Pieroni M, 2020,

    Phase decoherence of gravitational wave backgrounds

    , Physical Reveiw D

    Metric perturbations affect the phase of gravitational waves as theypropagate through the inhomogeneous universe. This effect causes StochasticGravitational Wave Backgrounds (SGWBs) to lose any phase coherence that mayhave been present at emission or horizon entry. We show that, for a standardcosmological model, this implies complete loss of coherence above frequencies$f \sim 10^{-12}$ Hz. The result is that any attempts to map SGWBs usingphase-coherent methods have no foreseeable applications. Incoherent methodsthat solve directly for the intensity of the SGWBs are the only methods thatcan reconstruct the angular dependence of any SGWB.
  • Journal article
    Erickson CW, Harrold AD, Leung R, Stelle KSet al., 2020,

    Covert symmetry breaking

    , The Journal of High Energy Physics, Vol: 2020, Pages: 1-26, ISSN: 1029-8479

    Reduction from a higher-dimensional to a lower-dimensional field theory can display special features when the zero-level ground state has nontrivial dependence on the reduction coordinates. In particular, a delayed ‘covert’ form of spontaneous symmetry breaking can occur, revealing itself only at fourth order in the lower-dimensional effective field theory action. This phenomenon is explored in a simple model of (d + 1)-dimensional scalar QED with one dimension restricted to an interval with Dirichlet/Robin boundary conditions on opposing ends. This produces an effective d-dimensional theory with Maxwellian dynamics at the free theory level, but with unusual symmetry breaking appearing in the quartic vector-scalar interaction terms. This simple model is chosen to illuminate the mechanism of effects which are also noted in gravitational braneworld scenarios.
  • Journal article
    Bourget A, Grimminger JF, Hanany A, Sperling M, Zafrir G, Zhong Zet al., 2020,

    Magnetic quivers for rank 1 theories

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    Hanany A, Zajac A, 2020,

    Ungauging schemes and Coulomb branches of non-simply laced quiver theories

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    Grimminger JF, Hanany A, 2020,

    Hasse diagrams for 3d N=4 quiver gauge theories - Inversion and the full moduli space

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    Magueijo J, Zlosnik T, Speziale S, 2020,

    Quantum cosmology of a dynamical Lambda

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 064006 – 1-064006 – 14, ISSN: 1550-2368

    By allowing torsion into the gravitational dynamics one can promote the cosmological constant Λ to a dynamical variable in a class of quasitopological theories. In this paper we perform a minisuperspace quantization of these theories in the connection representation. If Λ is kept fixed, the solution is a delta-normalizable version of the Chern-Simons (CS) state, which is the dual of the Hartle and Hawking and Vilenkin wave functions. We find that the CS state solves the Wheeler–De Witt equation also if Λ is rendered dynamical by an Euler quasitopological invariant, in the parity-even branch of the theory. In the absence of an infrared (IR) cutoff, the CS state suggests the marginal probability P(Λ)=δ(Λ). Should there be an IR cutoff (for whatever reason), the probability is sharply peaked at the cut off. In the parity-odd branch, however, we can still find the CS state as a particular (but not most general) solution, but further work is needed to sharpen the predictions. For the theory based on the Pontryagin invariant (which only has a parity-odd branch) the CS wave function no longer is a solution to the constraints. We find the most general solution in this case, which again leaves room for a range of predictions for Λ.
  • Journal article
    Ho DL-J, Rajantie A, 2020,

    Electroweak sphaleron in a strong magnetic field

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, ISSN: 1550-2368

    In an external magnetic field, the energy of the electroweak sphaleron—representing the energy barrier to baryon and lepton number violation—decreases but remains nonzero until the upper Ambjørn–Olesen critical field strength set by the Higgs mass and the electric charge. At this point the sphaleron energy vanishes. We demonstrate this by numerically computing the sphaleron configuration in the presence of an external magnetic field over the full range of field strengths until the energy barrier vanishes. We discuss the implications for baryogenesis in the early universe and the possibility of observing of baryon and lepton number violation in heavy-ion collisions.
  • Journal article
    Pieroni M, Barausse E, 2020,

    Foreground cleaning and template-free stochastic background extraction for LISA (vol 07, 021, 2020)

    , Journal of Cosmology and Astroparticle Physics, Vol: 2020, Pages: 1-3, ISSN: 1475-7516

    This erratum corrects the published version to keep track of a typo in the code, which artificially increased, by a factor ~ 2, the amplitude of the foreground from binaries of stellar origin black holes and neutron stars. While the conclusions of the paper are qualitatively unaffected, the figures and some numbers have been corrected accordingly. After correction, the SNR of the foreground as defined in the published version is ~ 53.
  • Journal article
    Barausse E, Berti E, Hertog T, Hughes SA, Jetzer P, Pani P, Sotiriou TP, Tamanini N, Witek H, Yagi K, Yunes N, Abdelsalhin T, Achucarro A, van Aelst K, Afshordi N, Akcay S, Annulli L, Arun KG, Ayuso I, Baibhav V, Baker T, Bantilan H, Barreiro T, Barrera-Hinojosa C, Bartolo N, Baumann D, Belgacem E, Bellini E, Bellomo N, Ben-Dayan I, Bena I, Benkel R, Bergshoefs E, Bernard L, Bernuzzi S, Bertacca D, Besancon M, Beutler F, Beyer F, Bhagwat S, Bicak J, Biondini S, Bize S, Blas D, Boehmer C, Boller K, Bonga B, Bonvin C, Bosso P, Bozzola G, Brax P, Breitbach M, Brito R, Bruni M, Bruegmann B, Bulten H, Buonanno A, Burko LM, Burrage C, Cabral F, Calcagni G, Caprini C, Cardenas-Avendano A, Celoria M, Chatziioannou K, Chernoff D, Clough K, Coates A, Comelli D, Compere G, Croon D, Cruces D, Cusin G, Dalang C, Danielsson U, Das S, Datta S, de Boer J, De Luca V, De Rham C, Desjacques V, Destounis K, Filippo FD, Dima A, Dimastrogiovanni E, Dolan S, Doneva D, Duque F, Durrer R, East W, Easther R, Elley M, Ellis JR, Emparan R, Ezquiaga JM, Fairbairn M, Fairhurst S, Farmer HF, Fasiello MR, Ferrari V, Ferreira PG, Ficarra G, Figueras P, Fisenko S, Foffa S, Franchini N, Franciolini G, Fransen K, Frauendiener J, Frusciante N, Fujita R, Gair J, Ganz A, Garcia P, Garcia-Bellido J, Garriga J, Geiger R, Geng C, Gergely LA, Germani C, Gerosa D, Giddings SB, Gourgoulhon E, Grandclement P, Graziani L, Gualtieri L, Haggard D, Haino S, Halburd R, Han W-B, Hawken AJ, Hees A, Heng IS, Hennig J, Herdeiro C, Hervik S, Holten JV, Hoyle CD, Hu Y, Hull M, Ikeda T, Isi M, Jenkins A, Julie F, Kajfasz E, Kalaghatgi C, Kaloper N, Kamionkowski M, Karas V, Kastha S, Keresztes Z, Kidder L, Kimpson T, Klein A, Klioner S, Kokkotas K, Kolesova H, Kolkowitz S, Kopp J, Koyama K, Krishnendu NV, Kroon JAV, Kunz M, Lahav O, Landragin A, Lang RN, Poncin-Lafitte CL, Lemos J, Li B, Liberati S, Liguori M, Lin F, Liu G, Lobo FSN, Loll R, Lombriser L, Lovelace G, Macedo RP, Madge E, Maggio E, Maggiore M, Marassi S, Marcoet al., 2020,

    Prospects for fundamental physics with LISA

    , General Relativity and Gravitation, Vol: 52, Pages: 1-33, ISSN: 0001-7701

    In this paper, which is of programmatic rather than quantitative nature, we aim to further delineate and sharpen the future potential of the LISA mission in the area of fundamental physics. Given the very broad range of topics that might be relevant to LISA,we present here a sample of what we view as particularly promising fundamental physics directions. We organize these directions through a “science-first” approach that allows us to classify how LISA data can inform theoretical physics in a variety of areas. For each of these theoretical physics classes, we identify the sources that are currently expected to provide the principal contribution to our knowledge, and the areas that need further development. The classification presented here should not be thought of as cast in stone, but rather as a fluid framework that is amenable to change with the flow of new insights in theoretical physics.
  • Journal article
    Alexander S, Jenks L, Jirousek P, Magueijo J, Zlosnik Tet al., 2020,

    Gravity waves in parity-violating Copernican universes

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 044039 – 1-044039 – 13, ISSN: 1550-2368

    In recent work minimal theories allowing the variation of the cosmological constant, Λ, by means of a balancing torsion, have been proposed. It was found that such theories contain parity violating homogeneous and isotropic solutions, due to a torsion structure called the Cartan spiral staircase. Their dynamics are controlled by Euler and Pontryagin quasitopological terms in the action. Here we show that such theories predict a dramatically different picture for gravitational wave fluctuations in the parity violating branch. If the dynamics are ruled solely by the Euler-type term, then linear tensor mode perturbations are entirely undetermined, hinting at a new type of gauge invariance. The Pontryagin term not only permits for phenomenologically sounder background solutions (as found in previous literature), but for realistic propagation of gravitational wave modes. These have the general property that the right and left handed gravitational waves propagate with different speeds. More generally they imply modified dispersion relations for the graviton, with both parity violating and non-violating deformations, including an effective mass for both gravitational wave polarizations. We discuss the observational constraints and predictions of these theories.
  • Journal article
    Magueijo J, 2020,

    Equivalence of the chern-simons state and the Hartle-Hawking and Vilenkin wave functions

    , PHYSICAL REVIEW D, Vol: 102, Pages: 044034 – 1-044034 – 7, ISSN: 1550-7998

    We show that the Chern-Simons (CS) state when reduced to minisuperspace is the Fourier dual of the Hartle-Hawking (HH) and Vilenkin (V) wave functions of the Universe. This is to be expected, given that the former and latter solve the same constraint equation, written in terms of conjugate variables (loosely, the expansion factor and the Hubble parameter). A number of subtleties in the mapping, related to the contour of integration of the connection, shed light on the issue of boundary conditions in quantum cosmology. If we insist on a real Hubble parameter, then only the HH wave function can be represented by the CS state, with the Hubble parameter covering the whole real line. For the V (or tunneling) wave function, the Hubble parameter is restricted to the positive real line (which makes sense, since the state only admits outgoing waves), but the contour also covers the whole negative imaginary axis. Hence, the state is not admissible if reality conditions are imposed upon the connection. Modifications of the V state, requiring the addition of source terms to the Hamiltonian constraint, are examined and found to be more palatable. In the dual picture, the HH state predicts a uniform distribution for the Hubble parameter over the whole real line; the modified V state a uniform distribution over the positive real line.
  • Journal article
    Pasarin O, Tseytlin AA, 2020,

    Generalised Schwarzschild metric from double copy of point-like charge solution in Born-Infeld theory

    , Physics Letters B, Vol: 807, Pages: 1-6, ISSN: 0370-2693

    We discuss possible application of the classical double copy procedure to construction of a generalisation of the Schwarzschild metric starting from an -corrected open string analogue of the Coulomb solution. The latter is approximated by a point-like charge solution of the Born-Infeld action, which represents the open string effective action for an abelian vector field in the limit when derivatives of the field strength are small. The Born-Infeld solution has a regular electric field which is constant near the origin suggesting that corrections from the derivative terms in the open string effective action may be small there. The generalization of the Schwarschild metric obtained by the double copy construction from the Born-Infeld solution looks non-singular but the corresponding curvature invariants still blow up at . We discuss the origin of this singularity and comment on possible generalizations.
  • Journal article
    Dowker F, Sorkin RD, 2020,

    Symmetry-breaking and zero-one laws

    , Classical and Quantum Gravity, Vol: 37, ISSN: 0264-9381

    We offer further evidence that discreteness of the sort inherent in a causal set cannot, in and of itself, serve to break Poincaré invariance. In particular we prove that a Poisson sprinkling of Minkowski spacetime cannot endow spacetime with a distinguished spatial or temporal orientation, or with a distinguished lattice of spacetime points, or with a distinguished lattice of timelike directions (corresponding respectively to breakings of reflection-invariance, translation-invariance, and Lorentz invariance). Along the way we provide a proof from first principles of the zero-one law on which our new arguments are based.
  • Journal article
    Contaldi CR, Pieroni M, Renzini A, Cusin G, Karnesis N, Peloso M, Ricciardone A, Tasinato Get al., 2020,

    Maximum likelihood map making with the Laser Interferometer Space Antenna

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 043502 – 1-043502 – 13, ISSN: 1550-2368

    Given the recent advances in gravitational-wave detection technologies, the detection and characterization of gravitational-wave backgrounds (GWBs) with the Laser Interferometer Space Antenna (LISA) is a real possibility. To assess the abilities of the LISA satellite network to reconstruct anisotropies of different angular scales and in different directions on the sky, we develop a map-maker based on an optimal quadratic estimator. The resulting maps are maximum likelihood representations of the GWB intensity on the sky integrated over a broad range of frequencies. We test the algorithm by reconstructing known input maps with different input distributions and over different frequency ranges. We find that, in an optimal scenario of well understood noise and high frequency, high SNR signals, the maximum scales LISA may probe are ℓmax≲15. The map-maker also allows to test the directional dependence of LISA noise, providing insight on the directional sky sensitivity we may expect.
  • Journal article
    Duff MJ, 2020,

    Weyl, Pontryagin, Euler, Eguchi and Freund

    , Journal of Physics A: Mathematical and Theoretical, Vol: 53, ISSN: 1751-8113

    In a September 1976 PRL Eguchi and Freund considered two topological invariants: the Pontryagin number $P\sim \int {\mathrm{d}}^{4}x\sqrt{g}{R}^{{\ast}}R$ and the Euler number $\chi \sim \int {\mathrm{d}}^{4}x\sqrt{g}{R}^{{\ast}}{R}^{{\ast}}$ and posed the question: to what anomalies do they contribute? They found that P appears in the integrated divergence of the axial fermion number current, thus providing a novel topological interpretation of the anomaly found by Kimura in 1969 and Delbourgo and Salam in 1972. However, they found no analogous role for χ. This provoked my interest and, drawing on my April 1976 paper with Deser and Isham on gravitational Weyl anomalies, I was able to show that for conformal field theories the trace of the stress tensor depends on just two constants: ${g}^{\mu \nu }\langle {T}_{\mu \nu }\rangle =\frac{1}{{\left(4\pi \right)}^{2}}\left(cF-aG\right)$ where F is the square of the Weyl tensor and $\int {\mathrm{d}}^{4}x\sqrt{g}G/{\left(4\pi \right)}^{2}$ is the Euler number. For free CFTs with N s massless fields of spin s $720c=6{N}_{0}+18{N}_{1/2}+72{N}_{1}720a=2{N}_{0}+11{N}_{1/2}+124{N}_{1}$.
  • Journal article
    Bourget A, Grimminger JF, Hanany A, Sperling M, Zhong Zet al., 2020,

    Magnetic quivers from brane webs with O5 planes

    , The Journal of High Energy Physics, Vol: 2020, Pages: 1-82, ISSN: 1029-8479

    Magnetic quivers have led to significant progress in the understanding of gauge theories with 8 supercharges at UV fixed points. For a given low-energy gauge theory realised via a Type II brane construction, there exist magnetic quivers for the Higgs branches at finite and infinite gauge coupling. Comparing these moduli spaces allows one to study the non-perturbative effects when transitioning to the fixed point. For 5d N = 1 SQCD, 5-brane webs have been an important tool for deriving magnetic quivers. In this work, the emphasis is placed on 5-brane webs with orientifold 5-planes which give rise to 5d theories with orthogonal or symplectic gauge groups. For this set-up, the magnetic quiver prescription is derived and contrasted against a unitary magnetic quiver description extracted from an O7− construction. Further validation is achieved by a derivation of the associated Hasse diagrams. An important class of families considered are the orthogonal exceptional En families (−∞ < n ≤ 8), realised as infinite coupling Higgs branches of Sp(k) gauge theories with fundamental matter. In particular, the moduli spaces are realised by a novel type of magnetic quivers, called unitary-orthosymplectic quivers.
  • Journal article
    de Rham C, Francfort J, Zhang J, 2020,

    Black hole gravitational waves in the effective field theory of gravity

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 024079 – 1-024079 – 14, ISSN: 1550-2368

    We investigate the propagation of gravitational waves on a black hole background within the low-energy effective field theory of gravity, where effects from heavy fields are captured by higher-dimensional curvature operators. Depending on the spin of the particles integrated out, the speed of gravitational waves at low energy can be either superluminal or subluminal as compared to the causal structure observed by other species. Interestingly, however, gravitational waves are always exactly luminal at the black hole horizon, implying that the horizon is identically defined for all species. We further compute the corrections on quasinormal frequencies caused by the higher-dimensional curvature operators and highlight the corrections arising from the low-energy effective field.
  • Journal article
    Drukker N, Giombi S, Tseytlin AA, Zhou Xet al., 2020,

    Defect CFT in the 6d (2,0) theory from M2 brane dynamics in AdS7×S4

    , The Journal of High Energy Physics, Vol: 2020, ISSN: 1029-8479

    Surface operators in the 6d (2,0) theory at large $N$ have a holographicdescription in terms of M2 branes probing the AdS$_7 \times S^4$ M-theorybackground. The most symmetric, 1/2-BPS, operator is defined over a planar orspherical surface, and it preserves a 2d superconformal group. This includes,in particular, an $SO(2,2)$ subgroup of 2d conformal transformations, so thatthe surface operator may be viewed as a conformal defect in the 6d theory. Thedual M2 brane has an AdS$_3$ induced geometry, reflecting the 2d conformalsymmetry. Here we use the holographic description to extract the defect CFTdata associated to the surface operator. The spectrum of transversefluctuations of the M2 brane is found to be in one-to-one correspondence with aprotected multiplet of operator insertions on the surface, which includes thedisplacement operator. We compute the one-loop determinants of fluctuations ofthe M2 brane, and extract the conformal anomaly coefficient of the sphericalsurface to order $N^0$. We also briefly discuss the RG flow from thenon-supersymmetric to the 1/2-BPS defect operator, and its consistency with a"$b$-theorem" for the defect CFT. Starting with the M2 brane action, we thenuse AdS$_3$ Witten diagrams to compute the 4-point functions of the elementarybosonic insertions on the surface operator, and extract some of the defect CFTdata from the OPE. The 4-point function is shown to satisfy superconformal Wardidentities, and we discuss a related subsector of "twisted" scalar insertions,whose correlation functions are constrained by the residual superconformalsymmetry.

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