Gauge-invariant quark and gluon fields in QCD: dynamics, topology, and the Gribov ambiguity

We review the implementation, in a temporal-gauge formulation of QCD, of the non-Abelian Gauss's law and the construction of gauge-invariant gauge and matter fields. We then express the QCD Hamiltonian in terms of these gauge-invariant operator-valued fields, and discuss the relation of this Hamiltonian and the gauge-invariant fields to the corresponding quantities in a Coulomb gauge formulation of QCD. We argue that a representation of QCD in terms of gauge-invariant quantities could be particularly useful for understanding low-energy phenomenology. We present the results of an investigation into the topological properties of the gauge-invariant fields, and show that there are Gribov copies of these gauge-invariant gauge fields, which are constructed in the temporal gauge, even though the conditions that give rise to Gribov copies do not obtain for the gauge-dependent temporal-gauge fields.Comment: 5 pages LaTex; talk presented at light-cone workshop "Particles and Strings", Trento, Italy, September 200

Destroying Hitler’s Berghof: The Bomber Command Raid of 25 April 1945

This paper examines the Royal Air Force raid on Adolf Hitler’s Berghof on the Obersalzberg in April 1945. Arthur Harris, the head of Bomber Command, wanted to emphasize the air power’s decisive role in the defeat of Nazism. However, Winston Churchill and Bernard Montgomery, among others, questioned the usefulness of destroying Berchtesgaden so late in the war. Unlike traditional explanations that focus on post–Dresden guilt, this article contends that British politicians grew increasingly concerned with the economic state of postwar Germany and the potential costs of the upcoming occupation. The continuation of area bombing at this late stage of the war reinforced the fears and consequences of “overkill.” Harris’s disconnect with postwar civil–military concerns negatively influenced the postwar image of Bomber Command

What can we learn about Gribov copies from a formulation of QCD in terms of gauge-invariant fields?

We review the procedure by which we implemented the non-Abelian Gauss's law and constructed gauge-invariant fields for QCD in the temporal (Weyl) gauge. We point out that the operator-valued transformation that transforms gauge-dependent temporal-gauge fields into gauge-invariant ones has the formal structure of a gauge transformation. We express the ``standard'' Hamiltonian for temporal-gauge QCD entirely in terms of gauge-invariant fields, calculate the commutation rules for these fields, and compare them to earlier work on Coulomb-gauge QCD. We also discuss multiplicities of gauge-invariant temporal-gauge fields that belong to different topological sectors and that, in previous work, were shown to be based on the same underlying gauge-dependent temporal-gauge fields. We relate these multiplicities of gauge-invariant fields to Gribov copies. We argue that Gribov copies appear in the temporal gauge, but not when the theory is represented in terms of gauge-dependent fields and Gauss's law is left unimplemented. There are Gribov copies of the gauge-invariant gauge field, which can be constructed when Gauss's law is implemented.Comment: To appear in Proceedings of the 6th Workshop on Non-Perturbative QCD, Paris, France, June 5-9, 200

Searches for LFV with CMS: leptoquarks with couplings to quarks of the 3rd generation

Leptoquarks (LQ) with couplings to the third generation of Standard Model (SM) quarks have been proposed as possible explanations of the flavour anomalies indicating the violation of lepton flavour universality (LFV). The CMS collaboration has initiated an extensive search programme for these new states in the LHC run-2 data recorded at $\sqrt{s}=13$ TeV. In this article, the CMS search results in the LQ pair-production final states $\tau b\,\tau b$, $\nu t\,\nu t$, $\nu b\,\nu b$, $\tau t\,\tau t$, and $\mu t\,\mu t$, as well as in the LQ single-production final state $\tau\,\tau b$ are discussed. No significant deviation from the SM is observed in any of these channels. For a broad range of LQ decay modes, exclusion limits on the LQ masses are determined at 95% confidence level reaching from 1.0 TeV to 1.8 TeV.Comment: Contribution to LHCP 2018, Bologna, Italy, 4-9 June 2018, 8 pages, 5 figure

Discovery Potential of MSSM Higgs Bosons with ATLAS

In this article the potential of the ATLAS experiment to discover MSSM Higgs bosons is discussed. Various Monte-Carlo studies for SM Higgs boson production and dedicated MSSM Higgs boson analyses are taken into account to investigate the discovery potential in four different CP-conserving MSSM benchmark scenarios, the Mh-max scenario, the no mixing scenario, the gluophobic scenario and the small alpha scenario. The most recent theoretical calculations are used for the prediction of Higgs masses and couplings. The results are shown for integrated luminosities of 30 and 300 inverse fb. With 300 inverse fb, a five sigma discovery of at least one Higgs boson state is possible in all scenarios for all values of tan beta and MA. The heavy neutral and charged Higgs states can only be discovered in parts of the parameter space.Comment: Presented at the 2005 International Europhysics Conference on High Energy Physics (EPS2005), Lisbon, Portugal, July 200

S-matrix elements for gauge theories with and without implemented constraints

We derive an expression for the relation between two scattering transition amplitudes which reflect the same dynamics, but which differ in the description of their initial and final state vectors. In one version, the incident and scattered states are elements of a perturbative Fock space, and solve the eigenvalue problem for the `free' part of the Hamiltonian --- the part that remains after the interactions between particle excitations have been `switched off'. Alternatively, the incident and scattered states may be coherent states that are transforms of these Fock states. In earlier work, we reported on the scattering amplitudes for QED, in which a unitary transformation relates perturbative and non-perturbative sets of incident and scattered states. In this work, we generalize this earlier result to the case of transformations that are not necessarily unitary and that may not have unique inverses. We discuss the implication of this relationship for Abelian and non-Abelian gauge theories in which the `transformed', non-perturbative states implement constraints, such as Gauss's law.Comment: 8 pages. Invited contribution to Foundation of Physics for an issue honoring Prof. Lawrence Horwitz on his 65th Birthda