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mitchell porter

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https://arxiv.org/abs/2103.13639

**Missing final state puzzle in the monopole-fermion scattering**

Ryuichiro Kitano, Ryutaro Matsudo

*[Submitted on 25 Mar 2021]*

It has been known that when a charged fermion scatters off a monopole, the fermion in the s-wave component must flip its chirality, i.e., fermion number violation must happen. This fact has led to a puzzle; if there are two or more flavors of massless fermions, any superposition of the fermion states cannot be the final state of the s-wave scattering as it is forbidden by conservation of the electric and flavor charges. The unitary evolution of the state vector, on the other hand, requires some interpretation of the final states. We solve the puzzle by finding new particle excitations in the monopole background, where multi-fermion operators exhibit condensation. The particles are described as excitations of closed-string configurations of the condensates.

https://arxiv.org/abs/2103.13574

**Quark-Gluon Plasma and Nucleons a la Laughlin**

Wei Lu

*[Submitted on 25 Mar 2021]*

Inspired by Laughlin's theory of the fractional quantum Hall effect, we propose a wave function for the quark-gluon plasma and the nucleons. In our model, each quark is transformed into a composite particle via the simultaneous attachment of a spin monopole and an isospin monopole. This is induced by the mesons endowed with both spin and isospin degrees of freedom. The interactions in the strongly-correlated quark-gluon system are governed by the topological wrapping number of the monopoles, which is an odd integer to ensure that the overall wave function is antisymmetric. The states of the quark-gluon plasma and the nucleons are thus uniquely determined by the combination of the monopole wrapping number m and the total quark number N. The radius squared of the quark-gluon plasma is expected to be proportional to mN. We anticipate the observation of such proportionality in the heavy ion collision experiments.

The first paper is a new detail of the "Callan-Rubakov effect", known since the early 1980s, in which conservation laws can be broken when a charged fermion scatters off a GUT monopole. A recent (2018) model of single-flavor baryons as a membrane ("pancake") bounded by a string, turns out to clarify a previously obscure aspect of the Callan-Rubakov dynamics. It's always nice when a theoretical innovation obtains unintended validation from a completely different application.

The second paper is more exotic. The author is proposing a new model of strongly interacting systems - not just the quark-gluon plasma, but also hadrons in general. In his model, each quark has a "spin monopole" and "isospin monopole" attached, which are topological solitons formed from a new "spin-isospin" meson field, represented using a Clifford algebra, something unusual for QCD... I emphasize that the author is not replacing QCD, but instead claiming that this is a valid approximation to the opaque dynamics of the strong interaction.

Curiously, along with monopoles, the papers have one more thing in common: the quantum Hall effect is in the background of both. The membranes of the first paper were introduced in 2018 as "quantum Hall droplets", and the new model of the second paper is inspired by Laughlin's quasiparticle model of the fractional quantum Hall effect.