Publications

Order by: publication date number of citations

• Extensions of realisations for low-dimensional Lie algebras

  Iryna Yehorchenko

  SciPost Phys. Proc. 14, 048 (2023) · published 24 November 2023 | Toggle abstract · pdf

  We find extensions of realisations of some low-dimensional Lie algebras, in particular, for the Poincaré algebra for one space dimension. Using inequivalent extensions, we performed comprehensive classification of relative differential invariants for these Lie algebras. We show difference between classification of extensions of realisations, and classification of nonlinear realisations of Lie algebras.

• The parastatistics of braided Majorana fermions

  Francesco Toppan

  SciPost Phys. Proc. 14, 046 (2023) · published 24 November 2023 | Toggle abstract · pdf

  This paper presents the parastatistics of braided Majorana fermions obtained in the framework of a graded Hopf algebra endowed with a braided tensor product. The braiding property is encoded in a t-dependent 4×4 braiding matrix $B_t$ related to the Alexander-Conway polynomial. The nonvanishing complex parameter t defines the braided parastatistics. At t=1 ordinary fermions are recovered. The values of t at roots of unity are organized into levels which specify the maximal number of braided Majorana fermions in a multiparticle sector. Generic values of t and the t=-1 root of unity mimick the behaviour of ordinary bosons.

• Construction of matryoshka nested indecomposable N-replications of Kac-modules of quasi-reductive Lie superalgebras, including the sl(m/n) and osp(2/2n) series

  Jean Thierry-Mieg, Peter D. Jarvis, Jerome Germoni, Maria Gorelik

  SciPost Phys. Proc. 14, 045 (2023) · published 24 November 2023 | Toggle abstract · pdf

  We construct a new class of finite dimensional indecomposable representations of simple superalgebras which may explain, in a natural way, the existence of the heavier elementary particles. In type I Lie superalgebras sl(m/n) and osp(2/2n), one of the Dynkin weights labeling the finite dimensional irreducible representations is continuous. Taking the derivative, we show how to construct indecomposable representations recursively embedding N copies of the original irreducible representation, coupled by generalized Cabibbo angles, as observed among the three generations of leptons and quarks of the standard model. The construction is then generalized in the appendix to quasi-reductive Lie superalgebras.

• Improved Galactic diffuse emission model strengthens the case for a Millisecond Pulsar explanation of the Fermi GeV excess

  Oscar Macias, Martin Pohl, Chris Gordon, Phaedra Coleman

  SciPost Phys. Proc. 12, 049 (2023) · published 4 July 2023 | Toggle abstract · pdf

  After more than a decade since its discovery, the Galactic center gamma-ray excess - discovered with the Fermi Large Area Telescope - remains puzzling. While the spectrum of the signal can be explained by either dark matter or an unresolved population of millisecond pulsars, the spatial morphology of this excess seems to hold the key to separate the two theories. In this contribution, we present the results of a recent study in which we use bleeding edge models for interstellar gas, inverse Compton emission, and stellar mass models to reanalyze the Galactic center excess. We find that the spatial morphology of the excess is highly correlated with stellar matter in the Galactic bulge, providing strong support for the millisecond pulsar hypothesis.

• Measurements of $t\bar{t}$ in association with charm quarks at 13 TeV with the ATLAS experiment

  Knut Zoch

  SciPost Phys. Proc. 18, 004 (2026) · published 29 January 2026 | Toggle abstract · pdf

  This talk presents the ATLAS Collaboration's first measurement of the inclusive cross-section for top-quark pair production in association with charm quarks. Using the full Run~2 proton--proton collision data sample at $\sqrt{s} = 13\,\text{TeV}$, collected with the ATLAS experiment at the LHC between 2015 and 2018, the measurement selects $t\bar{t}$ events with one or two charged leptons and at least one additional jet in the final state. A custom flavour-tagging algorithm is employed to simultaneously identify $b$-jets and $c$-jets. The fiducial cross-sections for $t\bar{t}+{≥}2c$ and $t\bar{t}+1c$ production are found to largely agree with predictions from various $t\bar{t}$ simulations, though all underpredict the observed values.

• Segal's contractions, AdS and conformal groups

  Daniel Sternheimer

  SciPost Phys. Proc. 14, 043 (2023) · published 24 November 2023 | Toggle abstract · pdf

  Symmetries and their applications always played an important role in I.E. Segal's work. I shall exemplify this, starting with his correct proof (at the Lie group level) of what physicists call the "O'Raifeartaigh theorem", continuing with his incidental introduction in 1951 of the (1953) Inönü-Wigner contractions, of which the passage from AdS (SO(2,3)) to Poincaré is an important example, and with his interest in conformal groups in the latter part of last century. Since the 60s Flato and I had many fruitful interactions with him around these topics. In a last section I succintly relate these interests in symmetries with several of ours, especially elementary particles symmetries and deformation quantization, and with an ongoing program combining both.

• Group theoretical derivation of consistent particle theories

  Giuseppe Nisticò

  SciPost Phys. Proc. 14, 040 (2023) · published 24 November 2023 | Toggle abstract · pdf

  Current quantum theories of an elementary free particle assume unitary space inversion and anti-unitary time reversal operators. In so doing robust classes of possible theories are discarded. The present work shows that consistent theories can be derived through a strictly deductive development from the principle of relativistic invariance and position covariance, also with anti-unitary space inversion and unitary time reversal operators. In doing so the class of possible consistent theories is extended for positive but also zero mass particles. In particular, consistent theories for a Klein-Gordon particle are derived and the non-localizability theorem for a non zero helicity massless particle is extended.

• Wigner function analysis of finite matter-radiation systems

  Eduardo Nahmad-Achar, Ramón López-Peña, Sergio Cordero, Octavio Castaños Garza

  SciPost Phys. Proc. 14, 039 (2023) · published 24 November 2023 | Toggle abstract · pdf

  We show that the behaviour in phase space of the Wigner function associated to the electromagnetic modes carries the information of both, the entanglement properties between matter and field, and the regions in parameter space where quantum phase transitions take place. A finer classification for the continuous phase transitions is obtained through the computation of the surface of minimum fidelity.

• Linear stability of Einstein and de Sitter universes in the quadratic theory of modified gravity

  Mudhahir Al-Ajmi

  SciPost Phys. Proc. 4, 012 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We consider the Einstein static and the de Sitter universe solutions and examine their instabilities in a subclass of quadratic modified theories for gravity. This modification proposed by Nash is an attempt to generalize general relativity. Interestingly, we discover that the Einstein static universe is unstable in the context of the modified gravity. In contrast to Einstein static universe, the de Sitter universe remains stable under metric perturbation up to the second order.

• Unitary Howe dualities in fermionic and bosonic algebras and related Dirac operators

  Guner Muarem

  SciPost Phys. Proc. 14, 038 (2023) · published 24 November 2023 | Toggle abstract · pdf

  In this paper we use the canonical complex structure $\mathbb{J}$ on $\mathbb{R}^{2n}$ to introduce a twist of the symplectic Dirac operator. This can be interpreted as the bosonic analogue of the Dirac operators on a Hermitian manifold. Moreover, we prove that the algebra of these Dirac operators is isomorphic to the Lie algebra $\mathfrak{su}(1,2)$ which leads to the Howe dual pair $(U(n),\mathfrak{su}(1,2))$.