Nuclear Theory·nucl-th

Friday·July 24, 2026

10 papers—5 primary·5 cross-listed

01
Gauge Auxiliary-Field Quantum Monte Carlo Method for Many-Fermion Systems
Zhaozhan Zhang
We propose novel Quantum Monte Carlo (QMC) methods for interacting many-fermion systems by leveraging the stochastic gauge freedom, originally developed in Gaussian phase-space QMC, within the phaseless auxiliary-field QMC (AFQMC) framework. In particular, we reinterpret the conventional force bias in phaseless AFQMC as a drift gauge and explore Fermi gauges based on natural orbitals of a reduced one-body density matrix defined via a mixed estimator, yielding stochastic, time-dependent Hartree-Fock-like dynamics. We propose a symmetry-projection sampling scheme to enhance the sampling efficiency. As a proof of concept, we apply these gauge-augmented AFQMC methods to a simple shell-model Hamiltonian: the Lipkin-Meshkov-Glick model. Numerical results illustrate the potential of stochastic gauges to enhance accuracy and reduce fluctuations, underscoring the promise for advancing these new techniques toward more realistic shell-model applications.
nucl-thcond-mat.str-el1 citation
02
Searching for initial state fluctuations in heavy ion collisions at FAIR energy using Principal Component Analysis
Ekata Nandy🇮🇳 · Subhasis Chattopadhyay🇮🇳
In high energy heavy ion collisions, the initial configurations of the colliding nuclei play an important role in determining the reaction type and the products of the reaction. The initial arrangement of nucleons within the overlap region of two colliding nuclei is generally asymmetric and such asymmetries reflect themselves in the measurement final state momentum anisotropy. Also initial distribution of the nucleons are subjected to large quantum fluctuation causing large energy deposition in a small region. The final state observables related momentum anisotropies although sensitive to such localized fluctuations but their true effect gets diluted because these observables are calculated by averaging over a set of events. Also, such fluctuations in the initial states are random and uncontrolled. Thus, identifying their effect from event-averaged final state observable is difficult. However, it would be interesting to know the origin of such fluctuations and how these fluctuation are eventually translated to the final state. In this work, we at first introduce such localized fluctuations in the initial configurations, also called hot spots, by implementing spatial rearrangements of nucleon position in the colliding nuclei in the central Pb+Pb collisions at E $_{l ab}$ =20 AGeV ( $s$ =6.27 GeV) using the UrQMD event generator. Then the final state distributions of one or two dimensional variables e.g., ( $η$ , $ϕ$ , $p_{T}$ ) and ( $η - p_{T}$ , $ϕ - p_{T}$ , $η - ϕ$ ) of the produced pions are analysed using the principal component analysis (PCA) technique. The eigenvalues of the principal components have been studied for various initial configurations, event fractions containing hot spots in the initial condition and for event centralities with an aim to find it's sensitivity to the initial hot spot configurations.
nucl-thhep-phEPJA(2025)·0 citations
03
Impact of Baryon anti-Baryon annihilation on hyperon ( $Λ$ , $Λ ˉ$ ) production and apparent strangeness enhancement in $Λ ˉ / p ˉ$ in heavy ion collisions at SPS energy
Ekata Nandy🇮🇳 · Subhasis Chattopadhyay🇮🇳
A deconfined medium of quarks and gluon, called the Quark-Gluon Plasma (QGP) is produced when heavy-nuclei are collided at relativistic energies. The QGP formation is often characterized by a phenomenon called strangeness enhancement where, the relative production of strange-to-non-strange particles are enhanced in central collisions compared to peripheral or proton-proton interactions. Besides the enhancement in K/ $π$ ratios, a non-monotonic energy dependence was also reported for $Λ ˉ$ to $p ˉ$ ratios at CERN SPS, attributed to a signature for the strangeness enhancement as well. As anti-particles are produced directly from the reaction, the $Λ ˉ$ / $p ˉ$ ratios are considered as a cleaner probe for the strangeness enhancement. However, at this energy range hadronic interactions have a dominant role to play and, importantly for $Λ ˉ$ and $p ˉ$ , processes like baryon-anti-baryon ( $B B ˉ$ ) annihilation can have a significant impact. In this work, we use a hadronic transport model UrQMD, to investigate the role of baryon-anti-baryon ( $B B ˉ$ ) annihilation on $Λ$ , $Λ ˉ$ hyperon production and its effect on $Λ ˉ$ / $p ˉ$ ratios. The UrQMD calculations that include $B B ˉ$ annihilation can produce the trend of average transverse mass spectra for $Λ$ and $Λ ˉ$ , as well as, the characteristic enhancement in $Λ ˉ$ / $p ˉ$ ratios in data as a function of centrality and collision energy. Furthermore, $Λ ˉ$ / $p ˉ$ ratios extracted from the feed-down corrected SPS data are seen to be in good agreement with UrQMD model calculations with $B B ˉ$ annihilation. This suggests that $Λ ˉ$ / $p ˉ$ enhancement is not necessarily because of strangeness enhancement and $B B ˉ$ annihilation has a significant role to play.
nucl-thhep-phEPJA(2022)·2 citations
04
Intrinsic coupling between transverse spherocity and elliptic flow in heavy-ion collisions
Subikash Choudhury🇮🇳 · Ekata Nandy🇮🇳
Transverse spherocity ( $S_{0}$ ) is an event-shape observable widely used to classify collision events according to their topology, particularly to distinguish jet-like from isotropic events. Low-spherocity events are generally interpreted as being associated with enhanced jet activity. This event classification has also been applied to heavy-ion collisions to investigate the influence of event topology on several observables, including elliptic flow and constituent-quark-number scaling. In this work, we demonstrate that such an interpretation requires careful reconsideration. Using toy Monte Carlo simulations, A Multiphase Transport (AMPT) model calculations, and an analytical formulation of the spherocity observable, we show that transverse spherocity is intrinsically related to the elliptic flow coefficient, $v_{2}$ . This connection arises because the axis that minimizes the spherocity aligns with the event symmetry plane, causing events with larger elliptic anisotropy to naturally exhibit smaller spherocity values even in the absence of genuine jet-like topologies. We further show that this intrinsic relation gives rise to an inherent anti-correlation between transverse spherocity and $v_{2}$ , implying that several characteristics previously attributed to the enhanced jet-like nature of low-spherocity events in heavy-ion collisions can instead be understood as consequences of collective anisotropic flow. Our results indicate that, in heavy-ion collisions, transverse spherocity should be interpreted primarily as a probe of the collective momentum-space anisotropy rather than as a direct measure of jetty event topology. Consequently, physics conclusions drawn from spherocity-selected events should explicitly account for its intrinsic correlation with elliptic flow.
nucl-thhep-phPRD(2026)·0 citations
05
Enhanced hydrodynamic predictions for $v_{02} (p_{T})$
Rupam Samanta🇵🇱 · Tribhuban Parida🇵🇱 · Jean-Yves Ollitrault🇫🇷
We present hydrodynamic predictions for the new observable $v_{02} (p_{T})$ , which measures the correlation of particle spectra with elliptic flow. We implement a data-driven correction so as to match hydrodynamic calculations to elliptic flow ( $v_{2} (p_{T})$ ) data. The corrected results are in fair agreement with $v_{0} (p_{T})$ data up to high $p_{T}$ . We make predictions for $v_{02} (p_{T})$ of unidentified charged hadrons up to $p_{T} = 10$ ~GeV $/ c$ , and of pions, kaons and protons up to $p_{T} = 5 - 6$ ~GeV $/ c$ , in several centrality windows, for Pb+Pb collisions at $s_{N N} = 5.02$ ~TeV. For $p_{T} > 4$ ~GeV $/ c$ , we predict a decrease of $v_{02} (p_{T})$ of charged hadrons in mid-central collisions, and meson-baryon splitting. We also predict a non-monotonic variation of $v_{02} (p_{T})$ for protons at low $p_{T}$ above $30%$ centrality. This is a specific feature of this new observable, which is not observed for the usual flow observables $v_{2} (p_{T})$ and $v_{0} (p_{T})$ .
nucl-thhep-phnucl-ex0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Gauge Auxiliary-Field Quantum Monte Carlo Method for Many-Fermion Systems

Searching for initial state fluctuations in heavy ion collisions at FAIR energy using Principal Component Analysis

Impact of Baryon anti-Baryon annihilation on hyperon (Λ, Λˉ) production and apparent strangeness enhancement in Λˉ/pˉ​ in heavy ion collisions at SPS energy

Intrinsic coupling between transverse spherocity and elliptic flow in heavy-ion collisions

Enhanced hydrodynamic predictions for v02​(pT​)

Affiliations

Impact of Baryon anti-Baryon annihilation on hyperon ( $Λ$ , $Λ ˉ$ ) production and apparent strangeness enhancement in $Λ ˉ / p ˉ$ in heavy ion collisions at SPS energy

Enhanced hydrodynamic predictions for $v_{02} (p_{T})$