Publications

Order by: publication date number of citations

• Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons

  Luciano L. Pappalardo, Gunar Schnell

  SciPost Phys. Proc. 8, 024 (2022) · published 11 July 2022 | Toggle abstract · pdf

  A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi- inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining single-spin and double-spin asymmetries for transverse target-polarization orientation.

• Adiabatic and irreversible classical discrete time crystals

  Adrian Ernst, Anna M. E. B. Rossi, Thomas M. Fischer

  SciPost Phys. 13, 091 (2022) · published 11 October 2022 | Toggle abstract · pdf

  We simulate the dynamics of paramagnetic colloidal particles that are placed above a magnetic hexagonal pattern and exposed to an external field periodically changing its direction along a control loop. The conformation of three colloidal particles above one unit cell adiabatically responds with half the frequency of the external field creating a time crystal at arbitrary low frequency. The adiabatic time crystal occurs because of the non-trivial topology of the stationary manifold. When coupling colloidal particles in different unit cells, many body effects cause the formation of topologically isolated time crystals and dynamical phase transitions between different adiabatic reversible and non-adiabatic irreversible space-time-crystallographic arrangements.

• Rapid detection of phase transitions from Monte Carlo samples before equilibrium

  Jiewei Ding, Ho-Kin Tang, Wing Chi Yu

  SciPost Phys. 13, 057 (2022) · published 9 September 2022 | Toggle abstract · pdf

  We found that Bidirectional LSTM and Transformer can classify different phases of condensed matter models and determine the phase transition points by learning features in the Monte Carlo raw data before equilibrium. Our method can significantly reduce the time and computational resources required for probing phase transitions as compared to the conventional Monte Carlo simulation. We also provide evidence that the method is robust and the performance of the deep learning model is insensitive to the type of input data (we tested spin configurations of classical models and green functions of a quantum model), and it also performs well in detecting Kosterlitz–Thouless phase transitions.

• Quark Sivers Function at Small-$x$: Leading contribution from the Spin-Dependent Odderon

  M. Gabriel Santiago

  SciPost Phys. Proc. 8, 027 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We present the calculation of the leading contribution to the quark Sivers function at small-Bjorken $x$. This calculation uses the high energy scattering approximation and operator formalism developed by Kovchegov and Sievert to obtain a dominant contribution to the quark Sivers function coming from the spin-dependent odderon, in agreement with the results of Dong, Zhen, and Zhou. We then calculate this dominant contribution in the diquark model of the proton to obtain a small-$x$ estimate for the Sivers function.

• Quasi-free limit in the deuteron-deuteron three-body break-up process

  R. Ramazani-Sharifabadi, H. R. Amir-Ahmadi, M. T. Bayat, I. Ciepał, M. Eslami-Kalantari, N. Kalantar-Nayestanaki, St. Kistryn, A. Kozela, M. Mahjour-Shafiei, H. Mardanpour, J. G. Messchendorp, M. Mohammadi-Dadkan, A. Ramazani-Moghaddam-Arani, E. Stephan, and H. Tavakoli-Zaniani

  SciPost Phys. Proc. 3, 057 (2020) · published 1 April 2020 | Toggle abstract · pdf

  Detailed measurements of vector and tensor analyzing powers of the 2H(d, dp)n breakup process are presented. The data were obtained using a polarized deuteron-beam with an energy of 65 MeV/nucleon impinging on a liquid-deuterium target. The experiment was conducted at the AGOR facility at KVI using the BINA 4Pi-detection system. The focus of this contribution is to analyze data of the dd scattering process in the regime at which the neutron acts as a spectator, which we refer to as the quasi-free (QF) limit. To achieve this, events for which the final-state deuteron and proton are coplanar have been analyzed and the data have been sorted for various reconstructed momenta of the missing neutron. In the limit of vanishing neutron momentum and at small deuteron-proton momentum transfer, the data match very well with measured and predicted spin observables of the elastic deuteron-proton scattering process. The agreement deteriorates rapidly with increasing neutron momentum and deuteron-proton momentum transfer. The results of coplanar configurations in four-body phase space are compared with the results of recent available theoretical calculations based on the Single-Scattering Approximation.

• Phase diagram for strong-coupling Bose polarons

  Arthur Christianen, J. Ignacio Cirac, Richard Schmidt

  SciPost Phys. 16, 067 (2024) · published 5 March 2024 | Toggle abstract · pdf

  Important properties of complex quantum many-body systems and their phase diagrams can often already be inferred from the impurity limit. The Bose polaron problem describing an impurity atom immersed in a Bose-Einstein condensate is a paradigmatic example. The interplay between the impurity-mediated attraction between the bosons and their intrinsic repulsion makes this model rich and interesting, but also complex to describe theoretically. To tackle this challenge, we develop a quantum chemistry-inspired computational technique and compare two variational methods that fully include both the boson-impurity and interboson interactions. We find one regime where the impurity-mediated interactions overcome the repulsion between the bosons, so that a sweep of the boson-impurity interaction strength leads to an instability of the polaron due to the formation of many-body clusters. If instead the interboson interactions dominate, the impurity will experience a crossover from a polaron into a few-body bound state. We achieve a unified understanding incorporating both of these regimes and show that they are experimentally accessible. Moreover, we develop an analytical model that allows us to interpret these phenomena in the Landau framework of phase transitions, revealing a deep connection of the Bose polaron model to both few- and many-body physics.

• Alibis of Exclusion: The role of ethnic economies in the differentiated inclusion of refugees in Berlin

  Jagat Sohail

  Mig. Pol. 2, 002 (2023) · published 11 July 2023 | Toggle abstract · pdf

  Neoliberal transformations in the field of asylum in Germany have, since 2016, placed an emphasis on labour market participation as the primary way through which refugees can establish long-term residence claims. Yet, while new arrivals are increasingly expected to rapidly integrate into this market, they are often armed with differential and precarious legal statuses which overwhelmingly determine the spheres of economic activity refugees can enter. This is especially true for the ever increasing number of rejected asylum seekers who are temporarily “tolerated”, for whom the only path to residence requires that they display their value as economic subjects to the German state. Based on ethnographic fieldwork conducted in Berlin between 2017 and 2020, I argue that, armed with little other than their cultural identities and networks, many refugees heavily relied on co-ethnic relationships to facilitate their participation in the labour market. The result is a displacement of the management of new diversity to ethnic economies, a move that disavows the marginalising consequences of the neoliberal transformations refugees are subject to. By masking a relationship between recently arrived migrants and the German economy and society as a relationship between migrants themselves, I argue that these practices work as alibis of exclusion.

• Quantized fragmentation of three-dimensional QCD string

  S. Todorova-Nova

  SciPost Phys. Proc. 10, 013 (2022) · published 10 August 2022 | Toggle abstract · pdf

  Recent developments of the model of quantized helical QCD string are presented, notably the baryon production. An overview of the experimental evidence is discussed as well as possible applications.

• The high-temperature expansion of the thermal sunset

  Andreas Ekstedt, Johan Löfgren

  SciPost Phys. Core 3, 008 (2020) · published 22 October 2020 | Toggle abstract · pdf

  We give a prescription for calculating the high-temperature expansion of the thermal sunset integral to arbitrary order. We derive all terms odd in $T$, and rederive previous results up to $\mathcal{O}(T^0) $ for both bosonic and fermionic thermal sunsets in dimensional regularisation. We perform analytical and numerical cross-checks. Intermediate steps involve integrals over three Bessel functions.

• Collective dynamics of heavy ion collisions in ATLAS

  Helena Santos

  SciPost Phys. Proc. 10, 034 (2022) · published 11 August 2022 | Toggle abstract · pdf

  The latest measurements of collective behaviour in a variety of collision systems with the ATLAS detector at the LHC, including pp collisions at 13 TeV, Xe+Xe collisions at 5.44 TeV, and Pb+Pb collisions at 5.02 TeV, are presented. They include vn-[pT] correlations, which carry important information about the initial-state geometry of the quark-gluon plasma and can shed light on any quadrupole deformation in the Xe nucleus, and measurements of flow decorrelations differential in rapidity, which probe the longitudinal structure of the colliding system. These measurements furthermore provide stringent tests of the theoretical understanding of the initial state in heavy ion collisions.