Publications

Order by: publication date number of citations

• Infrared properties of two-dimensional SU(N)/H nonlinear $\sigma$ models at nonzero $\theta$ angles

  Philippe Lecheminant, Yuya Tanizaki, Keisuke Totsuka

  SciPost Phys. 18, 183 (2025) · published 10 June 2025 | Toggle abstract · pdf

  A general strategy is proposed to explore the low-energy properties of two-dimensional nonlinear $\sigma$ models with $\theta$ terms. We demonstrate its application to nonlinear $\sigma$ models with the target space $SU(N)/H$, which include $\mathbb{C}P^{N-1}$, complex Grassmannian manifolds as well as the flag $SU(N)/U(1)^{N-1}$ and $SU(N)/SO(N)$ manifolds. By analyzing the symmetry and its anomaly content, we realize these nonlinear $\sigma$ models by considering specific deformations of the $SU(N)_1$ conformal field theory. For the flag-manifold $SU(N)/U(1)^{N-1}$ and $SU(N)/SO(N)$ models, those deformations are shown to correspond to the marginal current-current operator with the specific sign which leads to a massless renormalization group flow to the $SU(N)_1$ fixed point. In contrast, a massive regime with a two-fold ground-state degeneracy is found for the $\mathbb{C}P^{N-1}$ ($N >2$) and the Grassmannian nonlinear $\sigma$ models at $\theta=\pi$.

• Proton reconstruction with the Precision Proton Spectrometer (PPS) in Run 2 and the PPS at HL-LHC

  Fabrizio Ferro

  SciPost Phys. Proc. 8, 062 (2022) · published 12 July 2022 | Toggle abstract · pdf

  The Precision Proton Spectrometer (PPS) started operating in 2016 and has collected more than 110 fb$^{-1}$ of data over the course of the LHC Run 2, now fully available for physics analysis. This contribution covers the key features of the PPS alignment and optics calibration, which have been developed from scratch. The reconstructed proton distributions, the performance of the PPS simulation and finally the validation of the full reconstruction chain with physics data (dilepton events) are also illustrated.

• Thermoelectric coefficients and the figure of merit for large open quantum dots

  Robert S. Whitney, Keiji Saito

  SciPost Phys. 6, 012 (2019) · published 24 January 2019 | Toggle abstract · pdf

  We consider the thermoelectric response of chaotic or disordered quantum dots in the limit of phase-coherent transport, statistically described by random matrix theory. We calculate the full distribution of the thermoelectric coefficients (Seebeck $S$ and Peltier $\Pi$), and the thermoelectric figure of merit $ZT$, for large open dots at arbitrary temperature and external magnetic field, when the number of modes in the left and right leads ($N_{\rm L}$ and $N_{\rm R}$) are large. Our results show that the thermoelectric coefficients and $ZT$ are maximal when the temperature is half the Thouless energy, and the magnetic field is negligible. They remain small, even at their maximum, but they exhibit a type of universality at all temperatures, in which they do not depend on the asymmetry between the left and right leads $(N_{\rm L}-N_{\rm R})$, even though they depend on $(N_{\rm L}+N_{\rm R})$.

• Studying mass generation for gluons

  Gernot Eichmann, Jan M. Pawlowski

  SciPost Phys. Proc. 6, 018 (2022) · published 31 May 2022 | Toggle abstract · pdf

  In covariant gauges, the gluonic mass gap in Yang-Mills theory manifests itself in the basic observation that the massless pole in the perturbative gluon propagator disappears in nonperturbative calculations, but the origin of this behavior is not yet fully understood. We summarize a recent study of the respective dynamics with Dyson-Schwinger equations in Landau-gauge Yang-Mills theory. We identify the parameter that distinguishes the massive Yang-Mills regime from the massless decoupling solutions, whose endpoint is the scaling solution. Similar to the PT-BFM scheme, we find evidence that mass generation in the transverse sector is triggered by longitudinal massless poles.

• Recent jet and jet substructure measurements at the LHC, and ML based tagging

  Meena Meena

  SciPost Phys. Proc. 10, 022 (2022) · published 10 August 2022 | Toggle abstract · pdf

  Recent jet and jet substructure measurements at the LHC, and of machine-learning-based tagging techniques are presented using proton-proton collision data collected by the ATLAS and CMS experiments at CERN's Large Hadron Collider. These measurements are crucial for precise tests of electroweak and pQCD calculations and searches for physics beyond the Standard Model. The measurements are compared with several Monte Carlo event generator predictions which provide valuable input to the tuning of perturbative and non-perturbative models and to constraining model parameters of advanced parton-shower Monte Carlo programs.

• Drell-Yan $p_{\bot}$ with NLO-matched Parton Branching TMDs at energies from fixed-target to LHC

  Aleksandra Lelek

  SciPost Phys. Proc. 8, 029 (2022) · published 11 July 2022 | Toggle abstract · pdf

  The description of the Drell-Yan (DY) transverse momentum spectrum requires matching of fixed order QCD calculations with soft gluon resummation up to all orders in the QCD coupling. It has been noticed in the literature that a consistent description of DY data in a wide kinematic regime from fixed-target to LHC energies is problematic. In this talk the predictions for transverse momentum spectrum of DY data coming from experiments in very different kinematic ranges (NuSea, R209, Phenix, LHC 8 TeV and 13 TeV center-of-mass energies $\sqrt{s}$) are calculated by applying transverse momentum dependent (TMD) parton distributions obtained from the Parton Branching (PB) method, combined with the next-to-leading-order (NLO) calculation of the hard process in the MCatNLO method. We discuss the problems involved in matching of the fixed order calculation and resummation, especially in the moderate to low mass and $p_{\bot}$ region accessible at fixed target experiments. We find that at low DY mass and low $\sqrt{s}$ even in the region of $p_{\bot}/m_{DY}\sim 1$ the contribution of multiple soft gluon emissions (included in the PB-TMDs) is essential to describe the measurements, while at larger masses and LHC energies the contribution from soft gluons in the region of $p_{\bot}/m_{DY}\sim 1$ is small.

• Measurement of splittings along a jet shower in $\sqrt{s} = 200$ GeV pp collisions at STAR

  Raghav Kunnawalkam Elayavalli

  SciPost Phys. Proc. 8, 059 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Jets are algorithmic proxies of hard scattered partons, i.e. quarks and gluons, in high energy particle collisions. The STAR collaboration presents the first measurements of substructure observables at the first, second and third splits in the jet clustering tree via the iterative SoftDrop procedure. For each of these splits, we measure the fully corrected groomed shared momentum fraction (\zg) and groomed jet radius (\rg). We discuss the evolution of jet substructure in both the angular and momentum scales which allows for a self-similarity test of the DGLAP splitting function. We compare the fully corrected data to Monte Carlo models, providing stringent constraints on model parameters related to the parton shower and non-perturbative effects such as hadronization.

• Phase space compression of a positive muon beam in two spatial dimensions

  A. Antognini, N. J. Ayres, I. Belosevic, V. Bondar, A. Eggenberger, M. Hildebrandt, R. Iwai, K. Kirch, A. Knecht, G. Lospalluto, J. Nuber, A. Papa, M. Sakurai, I. Solovyev, D. Taqqu, T. Yan

  SciPost Phys. Core 8, 071 (2025) · published 20 October 2025 | Toggle abstract · pdf

  We present the first demonstration of simultaneous phase space compression in two spatial dimensions of a positive muon beam, the first stage of the novel high-brightness muon beam under development by the muCool collaboration at the Paul Scherrer Institute. The keV-energy, sub-mm size beam would enable a factor $10^5$ improvement in brightness for precision $\mu$SR, and atomic and particle physics measurements with positive muons. This compression is achieved within a cryogenic helium gas target with a strong density gradient, placed in a homogeneous magnetic field, under the influence of a complex electric field. In the next phase, the muon beam will be extracted into vacuum.

• Statistical mechanics of exponentially many low lying states

  Swapnamay Mondal

  SciPost Phys. 18, 103 (2025) · published 19 March 2025 | Toggle abstract · pdf

  It has recently been argued that for near-extremal black holes, the entropy and the energy above extremality respectively receive a $log T$ and a $T$-linear correction, where $T$ is the temperature. We show that both these features can be derived in a "low but not too low" temperature regime, by assuming the existence of exponentially many low lying states cleanly separated from rest of the spectrum, without using any specific theory. Argument of the logarithm in the expression of entropy is seen to be the ratio of temperature and the bandwidth of the low lying states. We argue that such spectrum might arise in non-supersymmetric extremal brane systems. Our findings strengthen Page's suggestion that there is no true degeneracy for non-supersymmetric extremal black holes.

• Testing Kubo formula on a nonlinear quantum conductor driven far from equilibrium, via power exchanges

  Zubair Iftikhar, Jonas Müller, Yuri Mukharsky, Philippe Joyez, Patrice Roche, Carles Altimiras

  SciPost Phys. 19, 127 (2025) · published 11 November 2025 | Toggle abstract · pdf

  We present an experimental test of Kubo formula performed on a nonlinear quantum conductor, a Superconductor-Insulator-Superconductor tunnel junction, driven far from equilibrium by a DC voltage bias. We implement the proposal of Lesovik & Loosen [G. B. Lesovik and R. Loosen, J. Exp. Theor. Phys. Lett. 65, 295 (1997)] and demonstrate experimentally that it is possible to extract both the emission and absorption noise of the conductor by measuring the power it exchanges with a linear detection circuit whose occupation is tuned close to vacuum levels. We then compare their difference to the real part of the admittance which is independently measured by coherent reflectometry, finding that Kubo formula holds within experimental accuracy. Last, we show theoretically that the spectral density of power exchanged between a quantum conductor and its linear detection circuit follows a Lesovik & Loosen like formula, even in the presence of strong detection back-action. This result applies as long as the conductor acts as a current source for the detection circuit and the detection circuit is not singular.