Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    de Rham C, Melville S, Noller J, 2021,

    Positivity bounds on dark energy: when matter matters

    , Journal of Cosmology and Astroparticle Physics, Vol: 2021, Pages: 1-25, ISSN: 1475-7516

    Positivity bounds — constraints on any low-energy effective field theory imposed by the fundamental axioms of unitarity, causality and locality in the UV — have recently been used to constrain scalar-tensor theories of dark energy. However, the coupling to matter fields has so far played a limited role. We show that demanding positivity when including interactions with standard matter fields leads to further constraints on the dark energy parameter space. We demonstrate how implementing these bounds as theoretical priors affects cosmological parameter constraints and explicitly illustrate the impact on a specific Effective Field Theory for dark energy. We also show in this model that the existence of a standard UV completion requires that gravitational waves must travel superluminally on cosmological backgrounds.
  • Journal article
    Page J, Magueijo J, 2021,

    Linking the Baum-Hawking-Coleman mechanism with unimodular gravity and Vilenkin's probability flux

    , Journal of Cosmology and Astroparticle Physics, Vol: 2021, Pages: 1-14, ISSN: 1475-7516

    We revisit a mechanism proposed by Hawking to resolve the cosmological constant problem (and the controversy it generated) to identify possibly more palatable alternatives and explore new connections and interpretations. In particular, through the introduction of a new action coupling the four-form field strength F = dA to the cosmological constant via a dynamical field λ(x), a novel Baum-Hawking-Coleman type mechanism is presented. This mechanism can be seen as a generalisation of Unimodular Gravity. A theory with a similar coupling to "F2" is also presented, with promising results. We show how in such theories the 3-form is closely related to the Chern-Simons density, and its associated definition of time. On the interpretational front, we propose a method avoiding the standard Euclidean action prescription, which makes use of Vilenkin's probability flux.
  • Journal article
    Goodhew H, Jazayeri S, Lee MHG, Pajer Eet al., 2021,

    Cutting cosmological correlators

    , Journal of Cosmology and Astroparticle Physics, Vol: 2021, ISSN: 1475-7516

    The initial conditions of our universe appear to us in the form of a classical probability distribution that we probe with cosmological observations. In the current leading paradigm, this probability distribution arises from a quantum mechanical wavefunction of the universe. Here we ask what the imprint of quantum mechanics is on the late time observables. We show that the requirement of unitary time evolution, colloquially the conservation of probabilities, fixes the analytic structure of the wavefunction and of all the cosmological correlators it encodes. In particular, we derive in perturbation theory an infinite set of single-cut rules that generalize the Cosmological Optical Theorem and relate a certain discontinuity of any tree-level n-point function to that of lower-point functions. Our rules are closely related to, but distinct from the recently derived Cosmological Cutting Rules. They follow from the choice of the Bunch-Davies vacuum and a simple property of the (bulk-to-bulk) propagator and are astoundingly general: we prove that they are valid for fields with a linear dispersion relation and any mass, any integer spin and arbitrary local interactions with any number of derivatives. They also apply to general FLRW spacetimes admitting a Bunch-Davies vacuum, including de Sitter, slow-roll inflation, power-law cosmologies and even resonant oscillations in axion monodromy. We verify the single-cut rules in a number of non-trivial examples, including four massless scalars exchanging a massive scalar, as relevant for cosmological collider physics, four gravitons exchanging a graviton, and a scalar five-point function.
  • Journal article
    Alday F, Argyres P, Lemos M, Martone M, Rastelli L, Taronna M, Mukhi S, Cordova L, He Y, Kruczenski M, Vieira P, Pomoni E, Bourget A, Hanany A, Fazzi M, Giacomelli S, Yamazaki M, Kristjansen C, Closset C, Zhou X, Bissi A, Sleight Cet al., 2021,

    The Pollica perspective on the (super)-conformal world

    , JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL, Vol: 54, ISSN: 1751-8113
  • Journal article
    Gould O, Ho DL-J, Rajantie A, 2021,

    Schwinger pair production of magnetic monopoles: momentum distribution for heavy-ion collisions

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 104, ISSN: 1550-2368

    Magnetic monopoles may be produced by the dual Schwinger effect in strong magnetic fields. Today, thestrongest known magnetic fields in the Universe are produced fleetingly in heavy-ion collisions. We use thecomplex worldline instanton method to calculate the momentum distribution of magnetic monopolesproduced in heavy-ion collisions, in an approximation that includes the effect of the magnetic field to allorders but neglects monopole self-interactions. The result saturates the preparation time-energy uncertaintyprinciple, and yields a necessary ingredient for experimental monopole searches in heavy-ion collisions.
  • Journal article
    Yao Q, Evans T, Chen B, Christensen KIMet al., 2021,

    Higher-order temporal network effects through triplet evolution

    , Scientific Reports, Vol: 11, Pages: 1-17, ISSN: 2045-2322

    We study the evolution of networks through ‘triplets’ — three-node graphlets. We develop a method to compute a transitionmatrix to describe the evolution of triplets in temporal networks. To identify the importance of higher-order interactions inthe evolution of networks, we compare both artificial and real-world data to a model based on pairwise interactions only.The significant differences between the computed matrix and the calculated matrix from the fitted parameters demonstratethat non-pairwise interactions exist for various real-world systems in space and time, such as our data sets. Furthermore,this also reveals that different patterns of higher-order interaction are involved in different real-world situations.To test our approach, we then use these transition matrices as the basis of a link prediction algorithm. We investigate ouralgorithm’s performance on four temporal networks, comparing our approach against ten other link prediction methods.Our results show that higher-order interactions in both space and time play a crucial role in the evolution of networks as wefind our method, along with two other methods based on non-local interactions, give the best overall performance. Theresults also confirm the concept that the higher-order interaction patterns, i.e., triplet dynamics, can help us understandand predict the evolution of different real-world systems.
  • Journal article
    Arav I, Gauntlett JP, Roberts MM, Rosen Cet al., 2021,

    Marginal deformations and RG flows for type IIB S-folds

    , The Journal of High Energy Physics, Vol: 2021, Pages: 1-41, ISSN: 1029-8479

    We construct a continuous one parameter family of AdS4 × S1 × S5 S-fold solutions of type IIB string theory which have nontrivial SL(2, ℤ) monodromy in the S1 direction. The solutions span a subset of a conformal manifold that contains the known N = 4 S-fold SCFT in d = 3, and generically preserve N = 2 supersymmetry. We also construct RG flows across dimensions, from AdS5 × S5, dual to N = 4, d = 4 SYM compactified with a twisted spatial circle, to various AdS4 ×S1 ×S5 S-fold solutions, dual to d = 3 SCFTs. We construct additional flows between the AdS5 dual of the Leigh-Strassler SCFT and an N = 2 S-fold as well as RG flows between various S-folds.
  • Journal article
    Karam A, Markkanen T, Marzola L, Nurmi S, Raidal M, Rajantie Aet al., 2021,

    Higgs-like spectator field as the origin of structure

    , European Physical Journal C: Particles and Fields, Vol: 81, ISSN: 1124-1861

    We show that the observed primordial perturbations can be entirely sourced by a light spectator scalar field with a quartic potential, akin to the Higgs boson, provided that the field is sufficiently displaced from vacuum during inflation. The framework relies on the indirect modulation of reheating, which is implemented without any direct coupling between the spectator field and the inflaton and does not require non-renormalisable interactions. The scenario gives rise to local non-Gaussianity with fNL≃5 as the typical signal. As an example model where the indirect modulation mechanism is realised for the Higgs boson, we study the Standard Model extended with right-handed neutrinos. For the Standard Model running we find, however, that the scenario analysed does not seem to produce the observed perturbation.
  • Journal article
    Beccaria M, Dunne G, Tseytlin AA, 2021,

    BPS Wilson loop in N=2 superconformal SU(N) "orientifold" gauge theory and weak-strong coupling interpolation

    , The Journal of High Energy Physics, Vol: 2021, Pages: 1-30, ISSN: 1029-8479

    We consider the expectation value ⟨W⟩ of the circular BPS Wilson loop in N = 2 superconformal SU(N) gauge theory containing a vector multiplet coupled to two hypermultiplets in rank-2 symmetric and antisymmetric representations. This theory admits a regular large N expansion, is planar-equivalent to N = 4 SYM theory and is expected to be dual to a certain orbifold/orientifold projection of AdS5 × S5 superstring theory. On the string theory side ⟨W⟩ is represented by the path integral expanded near the same AdS2 minimal surface as in the maximally supersymmetric case. Following the string theory argument in [5], we suggest that as in the N = 4 SYM case and in the N = 2 SU(N) × SU(N) superconformal quiver theory discussed in [19], the coefficient of the leading non-planar 1/N2 correction in ⟨W⟩ should have the universal λ3/2 scaling at large ’t Hooft coupling. We confirm this prediction by starting with the localization matrix model representation for ⟨W⟩. We complement the analytic derivation of the λ3/2 scaling by a numerical high-precision resummation and extrapolation of the weak-coupling expansion using conformal mapping improved Padé analysis.
  • Journal article
    Golat S, Contaldi CR, 2021,

    Geodesic noise and gravitational wave observations by pulsar timing arrays

    , Physics Letters B: Nuclear Physics and Particle Physics, Vol: 818, Pages: 1-4, ISSN: 0370-2693

    Signals from millisecond pulsars travel to us on geodesics along the line-of-sight that are affected by the space–time metric. The exact path-geometry and redshifting along the geodesics determine the observed Time-of-Arrival (ToA) of the pulses. The metric is determined by the distribution of dark matter, gas, and stars in the galaxy and, in the final stages of travel, by the distribution of solar system bodies. The inhomogeneous distribution of stellar masses can have a small but significant statistical effect on the ToAs through the perturbation of geodesics. This will result in additional noise in ToA observations that may affect Pulsar Timing Array (PTA) constraints on gravitational waves at very low frequencies. We employ a simple model for the stellar distribution in our galaxy to estimate the scale of both static and dynamic sources of what we term generically “geodesic noise”. We find that geodesic noise has a standard deviation of (10) ns for typical lines-of-sight. This suggests geodesic noise is relevant for estimates of PTA sensitivity and may limit future efforts for detection of gravitational waves by PTAs.
  • Journal article
    Magueijo J, 2021,

    Cosmological time and the constants of nature

    , Physics Letters B: Nuclear Physics and Particle Physics, Vol: 820, Pages: 1-4, ISSN: 0370-2693

    We propose that cosmological time is effectively the conjugate of the constants of nature. Different definitions of time arise, with the most relevant related to the constant controlling the dynamics in each epoch. The Hamiltonian constraint then becomes a Schrodinger equation. In the connection representation, it is solved by monochromatic plane waves moving in a space generalizing the Chern-Simons functional. Normalizable superpositions exist and for factorizable coherent states we recover the classical limit and a seamless handover between potentially disparate times. There is also a rich structure of alternative states, including entangled constants, opening up the doors to new phenomenology.
  • Journal article
    Magueijo J, 2021,

    Real Chern-Simons wave function

    , Physical Review D, Vol: 104, Pages: 1-10, ISSN: 2470-0010

    We examine the status of the Chern-Simons (or Kodama) state from the point of view of a formulation of gravity that uses only real connection and metric variables and a real action. We may package the real connection variables into the complex self-dual Ashtekar connection (and will do so to make contact with previous work), but that operation is essentially cosmetic and can be undone at any step or even bypassed altogether. The action will remain the (real) Einstein-Cartan action, forgoing the addition of the usual Holst (or Nieh-Yan) term with an imaginary coefficient. It is then found that the constraints are solved by a modification of the Chern-Simons state which is a pure phase (in the Lorentzian theory, we stress), the phase containing only the fully gauge-invariant imaginary part of the Chern-Simons functional. Thus, the state for the “real theory” is nonpathological with regards to the most egregious criticisms facing its “nonreal” cousin, solving the complex theory. A straightforward modification of the real Chern-Simons state is also a solution in quasitopological theories based on the Euler invariant, for which the cosmological constant, Λ, is dynamical. In that case it is enough to shift the usual factor of Λ in the wave function to the inside of the spatial Chern-Simons integral. The trick only works for the quasi-Euler theory with a critical coupling previously identified in the literature. It does not apply to the quasi-Pontryagin theory.
  • Journal article
    Chester SM, 2021,

    Anomalous dimensions of monopole operators in scalar QED3 with Chern-Simons term

    , Journal of High Energy Physics, Vol: 2021

    <jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>We study monopole operators with the lowest possible topological charge <jats:italic>q</jats:italic> = 1/2 at the infrared fixed point of scalar electrodynamics in 2 + 1 dimension (scalar QED<jats:sub>3</jats:sub>) with <jats:italic>N</jats:italic> complex scalars and Chern-Simons coupling <jats:italic>|k|</jats:italic> = <jats:italic>N</jats:italic>. In the large <jats:italic>N</jats:italic> expansion, monopole operators in this theory with spins <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \mathrm{\ell}&lt;O\left(\sqrt{N}\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ℓ</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mi>O</mml:mi> <mml:mfenced> <mml:msqrt> <mml:mi>N</mml:mi> </mml:msqrt> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> and associated flavor representations are expected to have the same scaling dimension to sub-leading order in 1/<jats:italic>N</jats:italic>. We use the state-operator correspondence to calculate the scaling dimension to sub-leading order with the result <jats:italic>N −</jats:italic> 0<jats:italic>.</jats:italic>2743 + <jats:italic>O</jats:italic>(1/<jats:italic>N</jats:italic>), which improves on existing leading order results. We also compute the <jats:italic>ℓ</jats:italic><jats:sup>2</jats:sup>/<jats:italic>N</jats:italic> term that breaks the degeneracy to sub-leading order for monopoles with
  • Journal article
    Ho DL-J, Rajantie A, 2021,

    Instanton solution for Schwinger production of 't Hooft-Polyakov monopoles

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 103, Pages: 1-9, ISSN: 1550-2368

    We present the results of an explicit numerical computation of a novel instanton in Georgi-Glashow SU(2) theory. The instanton is physically relevant as a mediator of Schwinger production of ’t Hooft–Polyakov magnetic monopoles from strong magnetic fields. In weak fields, the pair production rate has previously been computed using the worldline approximation, which breaks down in strong fields due to the effects of finite monopole size. Using lattice field theory we have overcome this limit, including finite monopole size effects to all orders. We demonstrate that a full consideration of the internal monopole structure results in an enhancement to the pair production rate, and confirm earlier results that monopole production becomes classical at the Ambjørn-Olesen critical field strength.
  • Journal article
    Alberte L, de Rham C, Jaitly S, Tolley AJet al., 2021,

    QED positivity bounds

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 103, Pages: 1-26, ISSN: 1550-2368

    We apply positivity bounds directly to a U(1) gauge theory with charged scalars and charged fermions, i.e., QED, minimally coupled to gravity. Assuming that the massless t-channel pole may be discarded, we show that the improved positivity bounds are violated unless new physics is introduced at the parametrically low scale Λnew∼(emMPl)1/2, consistent with similar results for scalar field theories, far lower than the scale implied by the weak gravity conjecture. This is sharply contrasted with previous treatments which focus on the application of positivity bounds to the low energy gravitational Euler-Heisenberg effective theory only. We emphasize that the low cutoff is a consequence of applying the positivity bounds under the assumption that the pole may be discarded. We conjecture an alternative resolution that a small amount of negativity, consistent with decoupling limits, is allowed and is not in conflict with standard UV completions, including weakly coupled ones.
  • Journal article
    Xie Y, Zhang J, Silva HO, de Rham C, Witek H, Yunes Net al., 2021,

    Square peg in a circular hole: choosing the right ansatz for isolated black holes in generic gravitational theories

    , Physical Review Letters, Vol: 126, Pages: 1-7, ISSN: 0031-9007

    The metric of a spacetime can be greatly simplified if the spacetime is circular. We prove that in generic effective theories of gravity, the spacetime of a stationary, axisymmetric, and asymptotically flat solution must be circular if the solution can be obtained perturbatively from a solution in the general relativity limit. This result applies to a broad class of gravitational theories that include arbitrary scalars and vectors in their light sector, so long as their nonstandard kinetic terms and nonmininal couplings to gravity are treated perturbatively.
  • Journal article
    Majidy S, Halliwell JJ, Laflamme R, 2021,

    Detecting violations of macrorealism when the original Leggett-Garg inequalities are satisfied

    , PHYSICAL REVIEW A, Vol: 103, ISSN: 2469-9926
  • Journal article
    Tolley AJ, Wang Z-Y, Zhou S-Y, 2021,

    New positivity bounds from full crossing symmetry

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    Cheamsawat K, Fischetti S, Wallis L, Wiseman Tet al., 2021,

    A surprising similarity between holographic CFTs and a free fermion in (2+1) dimensions

    , JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
  • Journal article
    Arav I, Cheung KCM, Gauntlett JP, Roberts MM, Rosen Cet al., 2021,

    A new family of AdS4 S-folds in type IIB string theory

    , The Journal of High Energy Physics, Vol: 2021, Pages: 1-49, ISSN: 1029-8479

    We construct infinite new classes of AdS4 × S1 × S5 solutions of type IIB string theory which have non-trivial SL(2, ℤ) monodromy along the S1 direction. The solutions are supersymmetric and holographically dual, generically, to N = 1 SCFTs in d = 3. The solutions are first constructed as AdS4 × ℝ solutions in D = 5 SO(6) gauged supergravity and then uplifted to D = 10. Unlike the known AdS4 × ℝ S-fold solutions, there is no continuous symmetry associated with the ℝ direction. The solutions all arise as limiting cases of Janus solutions of d = 4, N = 4 SYM theory which are supported both by a different value of the coupling constant on either side of the interface, as well as by fermion and boson mass deformations. As special cases, the construction recovers three known S-fold constructions, preserving N = 1, 2 and 4 supersymmetry, as well as a recently constructed N = 1 AdS4 × S1 × S5 solution (not S-folded). We also present some novel “one-sided Janus” solutions that are non-singular.
  • Journal article
    Jones H, 2021,

    Comment on 'Solvable model of bound states in the continuum (BIC) in on dimension' (Physica Scripta (2019) 94 105214)

    , Physica Scripta: an international journal for experimental and theoretical physics, Vol: 96, Pages: 1-4, ISSN: 0031-8949

    We elucidate the status of the special scattering states found in this paper and explore further the relationships between scattering states and bound states of different non-analytic segments (depending on midxmid) of the exponential potential.
  • Journal article
    Levine N, Tseytlin AA, 2021,

    Integrability vs. RG flow in G x G and G x G/H sigma models

    , The Journal of High Energy Physics, Vol: 2021, Pages: 1-32, ISSN: 1029-8479

    We consider a class of 2d σ-models on products of group spaces that provide new examples of a close connection between integrability and stability under the RG flow. We first study the integrable G × G model derived from the affine Gaudin construction (for which the 1-loop β-functions were found in arXiv:2010.07879) and show that its condition of integrability is preserved also by the 2-loop RG flow. We then investigate the RG flow in the gauged G × G/H model, in particular the integrable T1,1 model found in arXiv:2010.05573. We also construct a new class of integrable G × G/H models in the case when the subgroup H is abelian. In the simplest case of G = SU2, H = U1 this leads to an integrable σ-model on the T1,q space (with a particular B-field). This model is also shown to be stable under the 2-loop RG flow, and we relate this property to its invariance under T-duality in an isometric U1 direction. This T1,q model may be interpreted as an integrable deformation of the GMM model (of two coupled WZW theories with generic levels) away from the conformal point.
  • Journal article
    Magueijo J, Zlosnik T, 2021,

    Quantum torsion and a Hartle-Hawking beam

    , Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 103, Pages: 1-11, ISSN: 1550-2368

    In the Einstein-Cartan framework the torsion-free conditions arise within the Hamiltonian treatment as second-class constraints. The standard strategy is to solve these constraints, eliminating the torsion from the classical theory, before quantization. Here we advocate leaving the torsion inside the other constraints before quantization, leading at first to wave functions that can be called “kinematical” with regards to the torsion, but not the other constraints. The torsion-free condition can then be imposed as a condition upon the physical wave packets one constructs, satisfying the usual uncertainty relations, and so with room for quantum fluctuations in the torsion. This alternative strategy has the surprising effect of clarifying the sense in which the wave functions solving an explicitly real theory are “delta-function normalizable.” Such solutions with zero (or any fixed) torsion, should be interpreted as plane waves in torsion space. Properly constructed wave packets are therefore normalizable in the standard sense. Given that they are canonical duals, this statement applies equally well to the Chern-Simons state (connection representation) and the Hartle-Hawking wave function (metric representation). We show how, when torsion is taken into account, the Hartle-Hawking wave function is replaced by a Gauss-Airy function, with finite norm, which we call the Hartle-Hawking beam. The Chern-Simons state, instead, becomes a packet with a Gaussian probability distribution in connection space. We conclude the paper with two sections explaining how to generalize these results beyond minisuperspace.
  • Journal article
    Bugden M, Hulik O, Valach F, Waldram Det al., 2021,

    G-Algebroids: a unified framework for exceptional and generalised geometry, and poisson-lie duality

    , Fortschritte Der Physik/Progress of Physics, Vol: 69, Pages: 1-11, ISSN: 0015-8208

    We introduce the notion of urn:x-wiley:00158208:media:prop202100028:prop202100028-math-0001-algebroid, generalising both Lie and Courant algebroids, as well as the algebroids used in urn:x-wiley:00158208:media:prop202100028:prop202100028-math-0002 exceptional generalised geometry for urn:x-wiley:00158208:media:prop202100028:prop202100028-math-0003. Focusing on the exceptional case, we prove a classification of “exact” algebroids and translate the related classification of Leibniz parallelisable spaces into a tractable algebraic problem. After discussing the general notion of Poisson–Lie duality, we show that the Poisson–Lie U-duality is compatible with the equations of motion of supergravity.
  • Journal article
    Alexander S, Herczeg G, Magueijo J, 2021,

    A generalized Hartle-Hawking wave function

    , Classical and Quantum Gravity, Vol: 38, Pages: 1-15, ISSN: 0264-9381

    The Hartle–Hawking wave function is known to be the Fourier dual of the Chern–Simons or Kodama state reduced to mini-superspace, using an integration contour covering the whole real line. But since the Chern–Simons state is a solution of the Hamiltonian constraint (with a given ordering), its Fourier dual should provide a solution (i.e. beyond mini-superspace) of the Wheeler DeWitt equation representing the Hamiltonian constraint in the metric representation. We write down a formal expression for such a wave function, to be seen as the generalization beyond mini-superspace of the Hartle–Hawking wave function. Its explicit evaluation (or simplification) depends only on the symmetries of the problem, and we illustrate the procedure with anisotropic Bianchi models and with the Kantowski–Sachs model. A significant difference of this approach is that we may leave the torsion inside the wave functions when we set up the ansatz for the connection, rather than setting it to zero before quantization. This allows for quantum fluctuations in the torsion, with far reaching consequences.
  • Journal article
    Binder DJ, Chester SM, Jerdee M, Pufu SSet al., 2021,

    The 3d $$ \mathcal{N} $$ = 6 bootstrap: from higher spins to strings to membranes

    , Journal of High Energy Physics, Vol: 2021

    <jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>We study the space of 3d <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> = 6 SCFTs by combining numerical bootstrap techniques with exact results derived using supersymmetric localization. First we derive the superconformal block decomposition of the four-point function of the stress tensor multiplet superconformal primary. We then use supersymmetric localization results for 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> = 6 U(<jats:italic>N</jats:italic>)<jats:sub><jats:italic>k</jats:italic></jats:sub> × U(<jats:italic>N</jats:italic> + <jats:italic>M</jats:italic>)<jats:sub><jats:italic>−k</jats:italic></jats:sub> Chern-Simons-matter theories to determine two protected OPE coefficients for many values of <jats:italic>N, M, k</jats:italic>. These two exact inputs are combined with the numerical bootstrap to compute precise rigorous islands for a wide range of <jats:italic>N, k</jats:italic> at <jats:italic>M</jats:italic> = 0, so that we can non-perturbatively interpolate between SCFTs with M-theory duals at small <jats:italic>k</jats:italic> and string theory duals at large <jats:italic>k</jats:italic>. We also present evidence that the localization results for
  • Journal article
    Beccaria M, Tseytlin AA, 2021,

    1/N expansion of circular Wilson loop in N=2 superconformal SU(N) x SU(N) quiver

    , The Journal of High Energy Physics, Vol: 2021, Pages: 1-33, ISSN: 1029-8479

    Localization approach to N = 2 superconformal SU(N) × SU(N) quiver theory leads to a non-Gaussian two-matrix model representation for the expectation value of BPS circular SU(N) Wilson loop ⟨W⟩. We study the subleading 1/N2 term in the large N expansion of ⟨W⟩ at weak and strong coupling. We concentrate on the case of the symmetric quiver with equal gauge couplings which is equivalent to the ℤ2 orbifold of the SU(2N) N = 4 SYM theory. This orbifold gauge theory should be dual to type IIB superstring in AdS5 × (S5/ℤ2). We present a string theory argument suggesting that the 1/N2 term in ⟨W⟩ in the orbifold theory should have the same strong-coupling asymptotics λ3/2 as in the N = 4 SYM case. We support this prediction on the gauge theory side by a numerical study of the localization matrix model. We also find a relation between the 1/N2 term in the Wilson loop expectation value and the derivative of the free energy of the orbifold gauge theory on 4-sphere.
  • Journal article
    Chester SM, Green MB, Pufu SS, Wang Y, Wen Cet al., 2021,

    New modular invariants in $$ \mathcal{N} $$ = 4 Super-Yang-Mills theory

    , Journal of High Energy Physics, Vol: 2021

    <jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>We study modular invariants arising in the four-point functions of the stress tensor multiplet operators of 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, in the limit where <jats:italic>N</jats:italic> is taken to be large while the complexified Yang-Mills coupling <jats:italic>τ</jats:italic> is held fixed. The specific four-point functions we consider are integrated correlators obtained by taking various combinations of four derivatives of the squashed sphere partition function of 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> = 2<jats:sup><jats:italic>∗</jats:italic></jats:sup> theory with respect to the squashing parameter <jats:italic>b</jats:italic> and mass parameter <jats:italic>m</jats:italic>, evaluated at the values <jats:italic>b</jats:italic> = 1 and <jats:italic>m</jats:italic> = 0 that correspond to 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>
  • Conference paper
    Acharya B, Alexandre J, Beneš P, Bergmann B, Bevan A, Billoud T, Branzas H, Burian P, Campbell M, Cecchini S, Cho YM, de Montigny M, de Roeck A, Ellis JR, El Sawy MMH, Fairbairn M, Felea D, Frank M, Garvey D, Hays J, Hirt AM, Janecek J, Kalliokoski M, Korzenev A, Lacarrère DH, Leroy C, Levi G, Lionti A, Mánek P, Maulik A, Margiotta A, Mauri N, Mavromatos NE, Meduna L, Mermod P, Millward L, Mitsou VA, Ostrovskiy I, Ouimet PP, Papavassiliou J, Parker B, Patrizii L, Pavalas GE, Pinfold JL, Popa LA, Popa V, Pozzato M, Pospíšil S, Rajantie A, de Austri RR, Sahnoun Z, Sakellariadou M, Santra A, Sarkar S, Semenoff G, Shaa A, Sirri G, Sliwa K, Smolyanskiy P, Soluk R, Spurio M, Staelens M, Suk M, Tenti M, Togo V, Tuszynski JA, Upreti A, Vento V, Vives O, Wall A, White Eet al., 2021,

    Timepix3 as a solid-state time-projection chamber in particle and nuclear physics

    Timepix3 devices are hybrid pixel detectors developed within the Medipix3 collaboration at CERN providing a simultaneous measurement of energy (ToT) and time of arrival (ToA) in each of its 256 × 256 pixels (pixel pitch: 55 µm). The timestamp resolution below 2 ns allows a measurement of charge carrier drift times, so that particle trajectories can be reconstructed in 3D on a microscopic level (z-resolution: 30-60 µm). The 3D trajectory reconstruction methodology developed elsewhere is validated against simulated data providing ground truth information of the incident angles. The detector response functions and the achievable track angular resolutions are determined. For the first time, data taken with Timepix3 in the MoEDAL experiment are presented. After extracting singly charged minimum ionizing particle (MIP) tracks from the mixed radiation field using characteristic track features, their impact angles are evaluated. The directionality of the MIP radiation field is shown in elevation angle (?) versus azimuthal angle (?) maps, “unfolded” using the simulated detector responses to an omnidirectional radiation field.
  • Journal article
    Goodhew H, Jazayeri S, Pajer E, 2021,

    The Cosmological Optical Theorem

    , Journal of Cosmology and Astroparticle Physics, Vol: 2021, Pages: 021-021

    <jats:title>Abstract</jats:title> <jats:p>The unitarity of time evolution, or colloquially the conservation of probability, sits at the heart of our descriptions of fundamental interactions via quantum field theory. The implications of unitarity for scattering amplitudes are well understood, for example through the optical theorem and cutting rules. In contrast, the implications for in-in correlators in curved spacetime and the associated wavefunction of the universe, which are measured by cosmological surveys, are much less transparent. For fields of any mass in de Sitter spacetime with a Bunch-Davies vacuum and general local interactions, which need not be invariant under de Sitter isometries, we show that unitarity implies an infinite set of relations among the coefficients ψ<jats:sub> <jats:italic>n</jats:italic> </jats:sub> of the wavefunction of the universe with n fields, which we name Cosmological Optical Theorem. For contact diagrams, our result dictates the analytic structure of ψ<jats:sub> <jats:italic>n</jats:italic> </jats:sub> and strongly constrains its form. For example, any correlator with an odd number of conformally-coupled scalar fields and any number of massless scalar fields must vanish. For four-point exchange diagrams, the Cosmological Optical Theorem yields a simple and powerful relation between ψ<jats:sub>3</jats:sub> and ψ<jats:sub>4</jats:sub>, or equivalently between the bispectrum and trispectrum. As explicit checks of this relation, we discuss the trispectrum in single-field inflation from graviton exchange and self-interactions. Moreover, we provide a detailed derivation of the relation between the total-energy pole of cosmological correlators and flat-space amplitudes. We provide analogous formulae for sub-diagram singularities. Our results co

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.

Request URL: http://www.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=215&limit=30&resgrpMemberPubs=true&resgrpMemberPubs=true&page=9&respub-action=search.html Current Millis: 1741315047438 Current Time: Fri Mar 07 02:37:27 GMT 2025

Note to staff:  Adding new publications to a research group

  1. Log in to Symplectic.
  2. Click on Menu > Create Links
  3. Choose what you want to create links between – in this case ‘Publications’ and ‘Organisational structures’.
  4. Choose the organisational structure (research group) into which you want to link the publications and check the box next to it.
  5. 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. 
  6. Scroll to the bottom and click the blue ‘Create new link’ button to link them.
  7. 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.