Introducing groups into quantum theory (1926–1930)

In the second half of the 1920s, physicists and mathematicians introduced group-theoretic methods into the recently invented “new” quantum mechanics. Group representations turned out to be a highly useful tool in spectroscopy and in giving quantum-mechanical explanations of chemical bonds. H. Weyl explored the possibilities of a group-theoretic approach to quantization. In his second version of a gauge theory for electromagnetism, he even started to build a bridge between quantum theoretic symmetries and differential geometry. Until the early 1930s, an active group of young quantum physicists and mathematicians contributed to this new challenging field. But around the turn to the 1930s, opposition to the new methods in physics grew. This article focuses on the work of those physicists and mathematicians who introduced group-theoretic methods into quantum physics.     

Existence of solutions to a global eikonal equation

We derive a geometric necessary and sufficient condition for the existence of solutions to a global eikonal equation. We also study the existence of a minimal solution to this equation, and its relation with the well-known minimal time function.     

Effective gauge potentials induced by superconducting quantum circuits

We theoretically propose a scheme to induce non-Abelian and Abelian gauge potentials by the same superconducting circuit device. The level spacings of Cooper-pair box can be designed to resonantly match or largely detune from the mode frequencies of the one-dimensional transmission line resonators. We show the appearances of the effective gauge potentials via field quadrature operators. This scheme could help investigating the fundamental characteristics of the gauge theories with Josephson circuits.     

Quantization of gauge fields,graph polynomials and graph homology

We review quantization of gauge fields using algebraic properties of 3-regular graphs. We derive the Feynman integrand at n$n$ loops for a non-abelian gauge theory quantized in a covariant gauge from scalar integrands for connected 3-regular graphs, obtained from the two Symanzik polynomials.     

The angular momentum controversy: What’s it all about and does it matter?

The general question, crucial to an understanding of the internal structure of the nucleon, of how to split the total angular momentum of a photon or gluon into spin and orbital contributions is one of the most important and interesting challenges faced by gauge theories like Quantum Electrodynamics and Quantum Chromodynamics. This is particularly challenging since all QED textbooks state that such a splitting cannot be done for a photon (and a fortiori for a gluon) in a gauge-invariant way, yet experimentalists around the world are engaged in measuring what they believe is the gluon spin! This question has been a subject of intense debate and controversy, ever since, in 2008, it was claimed that such a gauge-invariant split was, in fact, possible. We explain in what sense this claim is true and how it turns out that one of the main problems is that such a decomposition is not unique and therefore raises the question of what is the most natural or physical choice. The essential requirement of measurability does not solve the ambiguities and leads us to the conclusion that the choice of a particular decomposition is essentially a matter of taste and convenience. In this review, we provide a pedagogical introduction to the question of angular momentum decomposition in a gauge theory, present the main relevant decompositions and discuss in detail several aspects of the controversies regarding the question of gauge invariance, frame dependence, uniqueness and measurability. We stress the physical implications of the recent developments and collect into a separate section all the sum rules and relations which we think experimentally relevant. We hope that such a review will make the matter amenable to a broader community and will help to clarify the present situation.     

Curve counting,instantons and McKay correspondences

We survey some features of equivariant instanton partition functions of topological gauge theories on four and six dimensional toric Kähler varieties, and their geometric and algebraic counterparts in the enumerative problem of counting holomorphic curves. We discuss the relations of instanton counting to representations of affine Lie algebras in the four-dimensional case, and to Donaldson–Thomas theory for ideal sheaves on Calabi–Yau threefolds. For resolutions of toric singularities, an algebraic structure induced by a quiver determines the instanton moduli space through the McKay correspondence and its generalizations. The correspondence elucidates the realization of gauge theory partition functions as quasi-modular forms, and reformulates the computation of noncommutative Donaldson–Thomas invariants in terms of the enumeration of generalized instantons. New results include a general presentation of the partition functions on ALE spaces as affine characters, a rigorous treatment of equivariant partition functions on Hirzebruch surfaces, and a putative connection between the special McKay correspondence and instanton counting on Hirzebruch–Jung spaces.     

Anomalies and Hawking Radiation of NUT-Kerr-Newman de Sitter Black Hole

Hawking radiation of NUT-Kerr-Newman de Sitter black hole is studied via anomalous point of view in this paper. The results show that the charged current and energy-momentum tensor fluxes, to restore gauge invariance and general coordinate covariance at the quantum level in the effective field theory, are exactly equal to those of Hawking radiation from the event horizon (EH) and the cosmological horizon (CH) of NUT-Kerr-Newman de Sitter black hole, respectively.     

On generalized Bäcklund transformations for equations describing pseudo-spherical surfaces

It is shown that each one-parameter subgroup of SL(2,R) gives rise to a local correspondence theorem between suitably generic solutions of arbitrary scalar equations describing pseudo-spherical surfaces. Thus, if appropriate genericity conditions are satisfied, there exist local transformations between any two solutions of scalar equations arising as integrability conditions of sl(2,R)-valued linear problems.

A complete characterization of evolution equations u_t=K(x,t,u,u_x,…,u_x^k) which are of strictly pseudo-spherical type is also provided.