3,977 research outputs found
Towards improved logarithmic descriptions of high energy processes involving jets in hadron colliders
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
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
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
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
LIPIcs, Volume 251, ITCS 2023, Complete Volum
Interfaces and Quantum Algebras, I: Stable Envelopes
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 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
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 Theories, Monopole Spectral Data & (Generalised) Cohomology Theories
We study Berry connections for supersymmetric ground states of 2d
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 , we show that the difference modules are
related to deformations of the equivariant quantum cohomology of , 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
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 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 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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