Publications

Order by: publication date number of citations

• NLO collinear factorization of large mass diphoton photoproduction amplitude

  Oskar Grocholski, Bernard Pire, Paweł Sznajder, Lech Szymanowski, Jakub Wagner

  SciPost Phys. Proc. 8, 078 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We calculate large mass diphoton exclusive photoproduction in the framework of collinear QCD factorization at next to leading order in {\alpha}s and at leading twist. Collinear divergences of the coefficient function are absorbed by the evolution of the generalized parton distributions (GPDs). This result enlarges the existing factorization proofs to 2 -> 3 processes, opening new reactions to a trustable extraction of GPDs.

• A large-$N$ approach to magnetic impurities in superconductors

  Chen-How Huang, Alejandro M. Lobos, Miguel A. Cazalilla

  SciPost Phys. 18, 087 (2025) · published 10 March 2025 | Toggle abstract · pdf

  Quantum spin impurities coupled to superconductors are under intense investigation for their relevance to fundamental research as well as the prospects to engineer novel quantum phases of matter. Here we develop a large-$N$ mean-field theory of a strongly coupled spin-$\tfrac{1}{2}$ quantum impurity in a conventional $s$-wave superconductor. The approach is benchmarked against Wilson's numerical renormalization group (NRG). While the large-$N$ method is not applicable in the weak-coupling regime where the Kondo temperature $T_K$ is smaller than the superconducting gap $\Delta$, it performs very well in the strong coupling regime where $T_K \gtrsim \Delta$, thus allowing us to obtain a reasonably accurate description of experimentally relevant quantities. The latter include the energy of the Yu-Shiba-Rusinov subgap states, their spectral weight, as well as the local density of continuum states. The method provides a reliable analytical tool that complements other perturbative and non-perturbative methods, and can be extended to more complex impurity models for which NRG may not be easily applicable.

• Physics from Photons at the LHC

  Lucian Harland-Lang

  SciPost Phys. Proc. 8, 072 (2022) · published 12 July 2022 | Toggle abstract · pdf

  LHC collisions can act as a source of photons in the initial state. This mechanism plays an important role in the production of particles with electroweak couplings, and a precise account of photon-initiated (PI) production at the LHC is a key ingredient in the LHC precision physics programme. I will discuss the possibility of modelling PI processes directly via the structure function approach. This can provide percent level precision in the production cross sections, and is therefore well positioned to account for LHC precision requirements. This formalism in addition allows one to make use of another useful feature of photons, namely that they are colour-singlet and can often be emitted elastically (or quasi-elastically) from the proton. I will discuss recent work on applications of the structure function approach to precision calculations of PI production in the inclusive mode, and to `exclusive' processes with rapidity gaps, which can provide a unique probe of the Standard Model and physics beyond it.

• Electronic structure of CeAuAl$_3$ using density functional theory

  André Deyerling, Marc A. Wilde, Christian Pfleiderer

  SciPost Phys. Proc. 11, 008 (2023) · published 5 June 2023 | Toggle abstract · pdf

  We studied the magnetic properties and electronic structure of $CeAuAl_3$ using density functional theory. This compound shows a large Sommerfeld coefficient, a Kondo temperature, ${T_K=4\,K}$ and antiferromagnetic order below ${T_N=1.1\,K}$. We calculated the magnetic groundstate of ${CeAuAl_3}$ and the magnetic anisotropy energies. Treating the 4f-electrons as localized with DFT+U we obtain a good match with the magnetic properties observed experimentally. We also report salient features of the electronic structure of ${CeAuAl_3}$, including features of the Fermi surface and associated quantum oscillatory spectra, when the 4f-electrons are treated either as localized or itinerant.

• Photoinduced pairing in Mott insulators

  Satoshi Ejima, Holger Fehske

  SciPost Phys. Proc. 11, 009 (2023) · published 5 June 2023 | Toggle abstract · pdf

  Utilizing time-evolution techniques in (infinite) matrix-product-state representation, we study the non-equilibrium dynamics of driven Mott insulators and demonstrate photoinduced $\eta$ pairing directly in the thermodynamic limit. Analyzing the time evolution of the corresponding pairing correlations, we determine the optimal laser pump parameters for which long-range $\eta$-pairing becomes dominant after pulse irradiation. The time-dependent photoemission spectra for this optimal pump parameter set show clear signatures of the photoinduced insulator-to-metal phase transition related to the formation of $\eta$ pairs.

• Sea Asymmetry from Polarized W Boson Production

  C. Cocuzza, A. Metz, N. Sato

  SciPost Phys. Proc. 8, 025 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We present the results of a global QCD analysis of helicity parton distribution functions (PDFs) that includes the latest polarized W-lepton production data from the STAR collaboration at the Relativistic Heavy-Ion Collider (RHIC). This data allows the first extraction of a nonzero helicity light-quark sea asymmetry within a simultaneous global QCD analysis of unpolarized and helicity PDFs.

• On the breakdown of dimensional reduction and supersymmetry in random-field models

  Gilles Tarjus, Matthieu Tissier, Ivan Balog

  SciPost Phys. 19, 001 (2025) · published 1 July 2025 | Toggle abstract · pdf

  We discuss the breakdown of the Parisi-Sourlas supersymmetry (SUSY) and of the dimensional-reduction (DR) property in the random field Ising and O($N$) models as a function of space dimension $d$ and/or number of components $N$. The functional renormalization group (FRG) predicts that this takes place below a critical line $d_\mathrm{DR}(N)$. We revisit the perturbative FRG results for the RFO($N$)M in $d=4+\epsilon$ and carry out a more comprehensive investigation of the nonperturbative FRG approximation for the RFIM. In light of this FRG description, we discuss the perturbative results in $\epsilon=6-d$ recently derived for the RFIM by Kaviraj, Rychkov, and Trevisani. We stress in particular that the disappearance of the SUSY/DR fixed point below $d_\mathrm{DR}$ arises as a consequence of the nonlinearity of the FRG equations and cannot be found via the perturbative expansion in $\epsilon=6-d$ (nor in $1/N$). We also provide an error bar on the value of the critical dimension $d_\mathrm{DR}$ for the RFIM, which we find around $5.11±0.09$, by studying several successive orders of the nonperturbative FRG approximation scheme.

• What do DVCS data tell us about TCS observables?

  O. Grocholski, H. Moutarde, B. Pire, P. Sznajder, J. Wagner

  SciPost Phys. Proc. 8, 070 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) leading twist amplitudes are intimately related thanks to their analytic properties as a function of $Q^2$. We exploit this feature to use Compton form factors previously extracted from available DVCS data and derive data-driven predictions for TCS observables to be measured in near future experiments. Our results quantitatively illustrate the complementarity of DVCS and TCS experiments.

• High field magnetism of the triangular lattice antiferromagnet CsFeCl$_3$ under high pressure

  Katsuki Nihongi, Takanori Kida, Yasuo Narumi, Nobuyuki Kurita, Hidekazu Tanaka, Yoshiya Uwatoko, Koichi Kindo, Masayuki Hagiwara

  SciPost Phys. Proc. 11, 012 (2023) · published 5 June 2023 | Toggle abstract · pdf

  Magnetization measurements of the triangular lattice antiferromagnet CsFeCl$_{3}$ at 1.4 K for $H \parallel c$ were performed in pulsed high magnetic fields of up to 51 T under high pressures of up to 0.80 GPa. At ambient pressure, the magnetization below $H_{\rm c1}$ = 4 T is small, and then it changes steeply between $H_{\rm c1}$ and $H_{\rm c2}$ = 12 T, followed by a gradual increase in magnetization up to $H_{\rm m}$ = 33 T where a two-step metamagnetic transition occurs. With increasing pressure, the $H_{\rm c1}$ and $H_{\rm m}$ shifted to the low-field side, while the $H_{\rm c2}$ shifted to the opposite side. The change in $H_{\rm m}$ may depend on the difference in the single-ion anisotropies on pressure in the lowest $J$ = 1 and the excited $J$ = 2 states.

• Hard exclusive $\pi^{+}n$ electro production beam spin asymmetries off the proton in the GPD and TDA regimes

  S. Diehl for the CLAS collaboration

  SciPost Phys. Proc. 8, 066 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Hard exclusive $\pi^{+}$n electro-production can be used to gain access to the 3D nucleon structure. The QCD factorisation mechanism in the "nearly forward region" ($t/Q^{2}$ small) allows a description by Generalized Parton Distributions (GPDs), while for the "nearly backward" kinematic region ($u/Q^{2}$ small) a description based on nucleon to pion transitions (TDAs) is available. The paper presents a measurement of single beam spin asymmetries to extract the $A^{\sin\phi}_{LU}$ moments and the related cross section ratio $\sigma_{LT^\prime}/\sigma_{0}$ from the hard exclusive $\pi^{+}$ channel off the unpolarized hydrogen target in a wide range of kinematics based on data taken with the CLAS spectrometer at Jefferson Lab. In addition, under forward angles a detailed multidimensional study will be presented based on CLAS12 data and compared to theoretical predictions.