3,977 research outputs found

    Towards improved logarithmic descriptions of high energy processes involving jets in hadron colliders

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    The total cross section for QCD processes at the LHC can be expanded perturbatively in the QCD coupling, αs, and then approximated by performing calculations in quantum field theory to a fixed order. However, in the presence of a large separation of energy scales, the convergence of this perturbative expansion is known to be damaged as higher order corrections in αs become more significant. High Energy Jets (HEJ) is a resummation framework designed to include contributions from high energy logarithms in the ratio of centre of mass energy to the transverse scale of particle produced to all orders in perturbation theory. These logs can become significant at the LHC and future colliders, and are significantly enhanced by the requirement of a large dijet invariant mass or large rapidity separation common in vector boson fusion/scattering (VBF/VBS) selection cuts. The work collected together in this thesis was done to extend the HEJ description of high energy collisions; both adding support for new, experimentally relevant processes at leading-log (LL) accuracy and improving the understanding of the currently supported processes. We present the first calculation of the leading log description of same-sign W W boson production plus jets at the LHC, which is important as a necessary background processes for vector boson scattering and which has high energy logarithms which are directly enhanced by VBS cuts. We compare the HEJ LL result to that of pure next-to-leading order and with next-to-leading order matched parton shower using the setup of a recent CMS experimental analysis. We then present results from studies looking at the impact of higher order corrections for two ongoing ATLAS experimental analyses. The setup of these analyses have directly lead to improvements in the HEJ description of both pure QCD jets and W plus jets which we describe in detail. Finally, we present a look ahead to the impact on the perturbative expansion of QCD at future colliders with a higher centre of mass energy, where we expect the impact of higher energy logarithms to be increasingly significant

    Quantum holographic surface anomalies

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    Expectation values of surface operators suffer from logarithmic divergences reflecting a conformal anomaly. In a holographic setting, where surface operators can be computed by a minimal surface in AdS, the leading contribution to the anomaly comes from a divergence in the classical action (or area) of the minimal surface. We study the subleading correction to it due to quantum fluctuations of the minimal surface. In the same way that the divergence in the area does not require a global solution but only a near-boundary analysis, the same holds for the quantum corrections. We study the asymptotic form of the fluctuation determinant and show how to use the heat kernel to calculate the quantum anomaly. In the case of M2-branes describing surface operators in the N=(2,0) theory in 6d, our calculation of the one-loop determinant reproduces expressions for the anomaly that have been found by less direct methods

    The infrared structure of perturbative gauge theories

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    Infrared divergences in the perturbative expansion of gauge theory amplitudes and cross sections have been a focus of theoretical investigations for almost a century. New insights still continue to emerge, as higher perturbative orders are explored, and high-precision phenomenological applications demand an ever more refined understanding. This review aims to provide a pedagogical overview of the subject. We briefly cover some of the early historical results, we provide some simple examples of low-order applications in the context of perturbative QCD, and discuss the necessary tools to extend these results to all perturbative orders. Finally, we describe recent developments concerning the calculation of soft anomalous dimensions in multi-particle scattering amplitudes at high orders, and we provide a brief introduction to the very active field of infrared subtraction for the calculation of differential distributions at colliders. © 2022 Elsevier B.V

    One-Loop Analytic Results for the Higgs Boson Plus Four Partons and Searches for Supersymmetry

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    In this thesis we present compact analytic expressions for the production of the Higgs boson plus two jets at one-loop mediated by both a scalar and a fermion. The results are derived using generalised unitarity methods and retain the full mass dependence of the mediating particle. We use the relationship between the fermion and scalar theories to simplify the algebra in the fermion theory; many of the required integral coefficients are identical and for those that differ, the difference is of a lower rank than the scalar result. We use these calculations to study the production of the Higgs boson plus two jets in the Minimal Supersymmetric Standard Model, assuming stop squarks are the dominant mediator. This is a potential channel for an indirect search for stop squarks, in particular we focus on the region where the lightest stop squark mass is similar to that of the top quark. However, although the 1-jet process shows improved discrimination over the inclusive process, we find there is no benefit gained from the 2-jet process

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Interfaces and Quantum Algebras, I: Stable Envelopes

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    The stable envelopes of Okounkov et al. realize some representations of quantum algebras associated to quivers, using geometry. We relate these geometric considerations to quantum field theory. The main ingredients are the supersymmetric interfaces in gauge theories with four supercharges, relation of supersymmetric vacua to generalized cohomology theories, and Berry connections. We mainly consider softly broken compactified three dimensional N=4\mathcal{N} =4 theories. The companion papers will discuss applications of this construction to symplectic duality, Bethe/gauge correspondence, generalizations to higher dimensional theories, and other topics.Comment: 152 pages; v2: references added, various explanations improve

    Anisotropies and modified gravity theories in stellar and substellar objects

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    In several classes of modified gravity theories, extra degrees of freedom are not completely screened in the interiors of stellar and substellar objects. In such theories, the hydrostatic equilibrium condition inside these objects is altered. Moreover, the interior structures of these objects might have a small pressure anisotropy induced by several physical phenomena, including rotation and magnetic fields. All these effects, both individually and collectively, induce changes in predicted stellar observables. Such changes have an impact on different phases of the stellar life cycle, starting from its birth to its death, covering almost all the branches of the Hertzsprung-Russell diagram. The aim of this work is to systematically review the current literature on the topic. We discuss the main results and constraints obtained on a class of modified gravity theories.Comment: This review article prepared for "Special Issue Metric-Affine Gravity Tartu", 49 pages, 10 figures, 3 tables, version accepted to Int. J. of Geometric Methods in Modern Physics (IJGMMP

    Berry Connections for 2d (2,2)(2,2) Theories, Monopole Spectral Data & (Generalised) Cohomology Theories

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    We study Berry connections for supersymmetric ground states of 2d N=(2,2)\mathcal{N}=(2,2) GLSMs quantised on a circle, which are generalised periodic monopoles, with the aim to provide a fruitful physical arena for mathematical constructions related to the latter. These are difference modules encoding monopole solutions due to Mochizuki, as well as an alternative algebraic description of solutions in terms of vector bundles endowed with filtrations. The simultaneous existence of these descriptions is an example of a Riemann-Hilbert correspondence. We demonstrate how these constructions arise naturally by studying the ground states as the cohomology of a one-parameter family of supercharges. Through this, we show that the two sides of this correspondence are related to two types of monopole spectral data that have a direct interpretation in terms of the physics of the GLSM: the Cherkis-Kapustin spectral variety (difference modules) as well as twistorial spectral data (vector bundles with filtrations). By considering states generated by D-branes and leveraging the difference modules, we derive novel difference equations for brane amplitudes. We then show that in the conformal limit, these degenerate into novel difference equations for hemisphere or vortex partition functions, which are exactly calculable. Beautifully, when the GLSM flows to a nonlinear sigma model with K\"ahler target XX, we show that the difference modules are related to deformations of the equivariant quantum cohomology of XX, whereas the vector bundles with filtrations are related to the equivariant K-theory.Comment: 52 pages + appendix, comments welcom

    Holography for the Trace Anomaly Action

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    A recently proposed effective action for the trace anomaly describes a tensor-scalar theory that is weakly coupled up to a certain high energy scale, where it becomes strongly interacting. Its ultraviolet completion is obtained by coupling to gravity a quantum field theory in which conformal invariance is spontaneously broken. In this paper, we show that if the field theory that gives rise to the trace anomaly is a large NcN_c conformal field theory, then the trace anomaly action has a completion above the strong scale in a holographic Randall-Sundrum two-brane theory, with the radion as a low energy remnant of the spontaneously broken conformal symmetry. Furthermore, we note that the sub-leading NcN_c terms can be derived by adding localized fields to the UV brane, so that the theory remains weakly coupled. The sub-leading terms are also obtained by introducing the Weyl squared terms in the 5D bulk. These, however, exhibit strongly coupled behavior at the respective sub-Planckian energy scales.Comment: 21 page
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