arXiv subjects

Sipaz Sharma

Publications and source records attributed to Sipaz Sharma.

16 recordsLinked to original sources

arXiv2026

Strong coupling constant from the 1-loop improved static energy

The static energy is an excellent observable for extracting the strong coupling $\alpha_s$ on the lattice. For short distances, the static energy can be calculated both on the lattice using Wilson line correlators, and with perturbation theory up to three loop accuracy with leading ultrasoft log resummation. Comparing the perturbative expression and lattice data allows for precise determination of $\alpha_s$. We present early results for 1-loop lattice perturbation theory improvement of the Wilson loop and show how it improves the $\alpha_s$ extraction. We present a preliminary reanalysis of the TUMQCD (2+1)-flavor QCD data.

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arXiv2026

Imprint of the adjoint meson spectrum in the decay patterns of hidden-bottom tetraquarks

We aim to clarify the experimentally observed near-degeneracy and decay patterns of the isospin, $I=1$, hidden-bottom tetraquarks $Z_b(10610)$ and $Z_b(10650)$ with quantum numbers $J^{P}=1^{+}$.We refer to them as $Z_b$ and $Z_b^{'}$, respectively. In particular, we find first evidence that the suppression of the decay of $Z_b^{'}$ to $B\bar{B^*}$ can be understood in the context of the Born-Oppenheimer Effective Field Theory (BOEFT). BOEFT enables writing both $Z_b$ and $Z_b^{'}$ as superpositions of $Z_1$ and $Z_2$ tetraquark configurations. This decomposition naturally relates the decay patterns of $Z_b$ and $Z_b^{'}$ to the degeneracy of the light degrees of freedom associated with $Z_1$ and $Z_2$ tetraquarks, {\it i.e.,} $1^{--}$and $0^{-+}$ adjoint mesons, respectively. By calculating the adjoint meson correlators within the framework of lattice QCD, we get good indications that these adjoint mesons are degenerate.

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arXiv2026

Studying the QCD phase diagram using pressure derivatives from lattice QCD

We summarize the application of derivatives of the QCD pressure, calculated within the framework of lattice QCD, in constructing observables that probe aspects of the QCD phase diagram at physical quark masses. We outline how the behavior of energy-like and magnetization-like observables at physical quark masses is influenced by the $(2+1)$-flavor chiral phase transition. We describe features of the chiral crossover at vanishing and non-vanishing chemical potentials and discuss deconfinement at zero chemical potential. We address the relevance of the convergence properties of the Taylor expansion of the QCD pressure in the search for the QCD critical endpoint.

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arXiv2025

Generalized susceptibilities and the properties of charm degrees of freedom across the QCD crossover temperature

We study the generalized charm susceptibilities in 2+1 flavor QCD on the lattice at several lattice spacings. We show that, below the chiral crossover, these susceptibilities are well described by the hadron resonance gas (HRG) model if charmed hadrons not listed in tables of the Particle Data Group are included. However, the HRG description abruptly breaks down just above the chiral crossover. To understand this, we use a model for the charm pressure in which it is expressed as the sum of partial pressures from charmed baryons, charmed mesons, and charm quarks. We present continuum estimates of these partial pressures and find that, while the partial pressures of charmed mesons and baryons drop below their respective HRG predictions, the charm quark pressure becomes non-zero above the chiral crossover.

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arXiv2025

Continuum limit of generalized charm susceptibilities

We investigate in detail the sensitivity of the fourth-order charm fluctuation, calculated on the lattice, to the input bare charm quark mass. We approach its continuum limit by employing four different lines of constant physics. We quantify the cutoff effects arising due to bare charm quark mass for both coarser and finer lattices. Finally, we show that the ratios of generalized charm susceptibilities, calculated on coarser lattices, and the continuum-extrapolated fourth-order charm fluctuation are sufficient to obtain the continuum limit of all physical observables relevant to open charm physics.

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arXiv2025

Thermodynamics of charmed hadrons across chiral crossover from lattice QCD

We use up to fourth-order charm fluctuations and their correlations with net baryon number, electric charge, and strangeness fluctuations, calculated within the framework of lattice QCD, to study the continuum partial pressure contributions of charmed baryons and mesons. We show that, at and below the chiral crossover temperature, these partial pressures receive enhanced contributions from experimentally unobserved charmed hadrons predicted by the Quark Model. Additionally, we demonstrate that at the chiral crossover, the Hadron Resonance Gas description breaks down, signaling the modification of open charm hadrons and thereby implying the onset of charm deconfinement. We present evidence for the survival of low-lying non-radial $1S$ and $1P$ hadron-like excitations above the chiral crossover, which hints at the sequential melting of charmed hadrons. Finally, we investigate the continuum partial pressure contribution of charm quark-like excitation that emerges at the chiral crossover and calculate its temperature-dependent in-medium mass.

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arXiv2024

Towards a parameter-free determination of critical exponents and chiral phase transition temperature in QCD

In order to quantify the universal properties of the chiral phase transition in (2+1)-flavor QCD, we make use of an improved, renormalized order parameter for chiral symmetry breaking which is obtained as a suitable difference of the $2$-flavor light quark chiral condensate and its corresponding light quark susceptibility. Having no additive ultraviolet as well as multiplicative logarithmic divergences, we use ratios of this order parameter constructed from its values for two different light quark masses. We show that this facilitates determining in a parameter-independent manner, the chiral phase transition temperature $T_c$ and the associated critical exponent $\delta$ which, for sufficiently small values of the light quark masses, controls the quark mass dependence of the order parameter at $T_c$. We present first results of these calculations from our numerical analysis performed with staggered fermions on $N_\tau=8$ lattices.

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arXiv2024

Aspects of the chiral crossover transition in (2+1)-flavor QCD with M\"{o}bius domain-wall fermions

The non-singlet part of the chiral symmetry in QCD with two light flavors is known to be restored through a crossover transition at a pseudo-critical temperature. However, the temperature dependence of the singlet part of the chiral symmetry and whether it is effectively restored at the same temperature is not well understood. Using (2+1)-flavor QCD configurations generated using the M\"{o}bius domain-wall discretization on an $N_\tau=8$ lattice, we construct suitable observables where the singlet and non-singlet chiral symmetries are disentangled in order to study their temperature dependence across the crossover transition. From the peak of the disconnected part of the chiral susceptibility, we obtain a pseudo-critical temperature $T_{pc}=158.7{}_{{}-2.3}^{{}+2.6}$ MeV where the non-singlet part of the chiral symmetry is effectively restored. From a calculation of the topological susceptibility and its temperature dependence we find that the singlet $U_A(1)$ part of the chiral symmetry is not effectively restored at $T<186$ MeV.

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arXiv2024

Persistence of charmed hadrons in QGP from lattice QCD

We study the nature of charm degrees of freedom near the chiral crossover based on lattice QCD calculations of the second and fourth-order cumulants of charm fluctuations, and their correlations with net baryon number, electric charge, and strangeness fluctuations. We show that below the chiral crossover temperature, $T_{pc}$, the thermodynamics of charm can be very well understood in terms of charmed hadrons. We present evidence that above $T_{pc}$, however, charm quark-like excitations emerge as new degrees of freedom contributing to the partial charm pressure. Nonetheless, up to temperatures as high as 175 MeV, charmed hadron-like excitations significantly contribute to the partial charm pressure.

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arXiv2024

Curvature of the chiral phase transition line from the magnetic equation of state of (2+1)-flavor QCD

We analyze the dependence of the chiral phase transition temperature on baryon number and strangeness chemical potentials by calculating the leading order curvature coefficients in the light and strange quark flavor basis as well as in the conserved charge ($B, S$) basis. Making use of scaling properties of the magnetic equation of state (MEoS) and including diagonal as well as off-diagonal contributions in the expansion of the energy-like scaling variable that enters the parametrization of the MEoS, allows to explore the variation of $T_c(\mu_B,\mu_S) = T_c ( 1 - (\kappa_2^B \hat{\mu}_B^2 + \kappa_2^S \hat{\mu}_S^2 + 2\kappa_{11}^{BS} \hat{\mu}_B \hat{\mu}_S))$ along different lines in the $(\mu_B,\mu_S)$ plane. On lattices with fixed cut-off in units of temperature, $aT=1/8$, we find $\kappa_2^B=0.015(1)$, $\kappa_2^S=0.0124(5)$ and $\kappa_{11}^{BS}=-0.0050(7)$. We show that the chemical potential dependence along the line of vanishing strangeness chemical potential is about 10\% larger than along the strangeness neutral line. The latter differs only by about $3\%$ from the curvature on a line of vanishing strange quark chemical potential, $\mu_s=0$. We also show that close to the chiral limit the strange quark mass contributes like an energy-like variable in scaling relations for pseudo-critical temperatures. The chiral phase transition temperature decreases with decreasing strange quark mass, $T_c(m_s)= T_c(m_s^{\rm phy}) (1 - 0.097(2) (m_s-m_s^{\rm phys})/m_s^{\rm phy}+{\cal O}((\Delta m_s)^2)$.

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arXiv2024

Charm degrees of freedom in hot matter from lattice QCD

We study the nature of charm degrees of freedom in hot strong interaction matter by performing lattice QCD calculations of the second and fourth-order cumulants of charm fluctuations, and their correlations with net baryon number, electric charge and strangeness fluctuations. We show that below the chiral crossover temperature thermodynamics of charm can be very well understood in terms of charmed hadrons. Above the chiral transition charm quarks show up as new degrees of freedom contributing to the partial charm pressure. However, up to temperatures as high as 175 MeV charmed hadron-like excitations provide a significant contribution to the partial charm pressure.

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arXiv2024

Charm Fluctuations and Deconfinement

We establish that the charmed hadrons start dissociating at the chiral crossover temperature, ${T_{pc}}$, leading to the appearance of charm degrees freedom carrying fractional baryon number. Our method is based on analyzing the second and fourth-order cumulants of charm (${C}$) fluctuations, and their correlations with baryon number (${B}$), electric charge (${Q}$) and strangeness (${S}$) fluctuations. The first-time calculation of the ${QC}$ correlations on the high statistics datasets of the HotQCD Collaboration enables us to disentangle the contributions from different electrically-charged charm subsectors in the hadronic phase. In particular, we see an enhancement over the PDG expectation in the fractional contribution of the ${|Q|}=2$ charm subsector to the total charm partial pressure for ${T<T_{pc}}$; this enhancement is in agreement with the Quark Model extended Hadron Resonance Gas (QM-HRG) model calculations. Furthermore, the agreement of QM-HRG calculations with the projections onto charmed baryonic and mesonic correlations in different charm subsectors indicates the existence of not-yet-discovered charmed hadrons in all charm subsectors below ${T_{pc}}$. We aim at determining the relevant degrees of freedom in temperature range ${T_{pc}<T<340 \text{ MeV}}$ by assuming the existence of a non-interacting gas of charmed quasi-particles composed of meson, baryon and quark-like excitations above $T_{pc}$. Our data suggest that the particles with quantum numbers consistent with quarks start appearing at $T_{pc}$.

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arXiv2023

Equation of state and speed of sound of (2+1)-flavor QCD in strangeness-neutral matter at non-vanishing net baryon-number density

We update results on the QCD equation of state in (2+1)-flavor QCD with non-zero conserved charge chemical potentials obtained from an eighth-order Taylor series. We present results for basic bulk thermodynamic observables of strangeness-neutral strong-interaction matter, i.e. pressure, number densities, energy and entropy density, and resum Taylor series results using Padé approximants. Furthermore, we calculate the speed of sound as well as the adiabatic compression factor of strangeness-neutral matter on lines of constant entropy per net baryon number. We show that the equation of state ($P(n_B), ε(n_B)$) is already well described by the $4^{\rm th}$-order Taylor series in almost the entire range of temperatures accessible with the beam energy scan in collider mode at the Relativistic Heavy Ion Collider.

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arXiv2023

Phase Transitions in Particle Physics -- Results and Perspectives from Lattice Quantum Chromo-Dynamics

Phase transitions in a non-perturbative regime can be studied by ab initio Lattice Field Theory methods. The status and future research directions for LFT investigations of Quantum Chromo-Dynamics under extreme conditions are reviewed, including properties of hadrons and of the hypothesized QCD axion as inferred from QCD topology in different phases. We discuss phase transitions in strong interactions in an extended parameter space, and the possibility of model building for Dark Matter and Electro-Weak Symmetry Breaking. Methodological challenges are addressed as well, including new developments in Artificial Intelligence geared towards the identification of different phases and transitions.

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arXiv2023

Charm fluctuations in (2+1)-flavor QCD at high temperature

Using the high statistics datasets of the HotQCD Collaboration, generated with the HISQ (2+1)-flavor action for light and strange quarks, and treating the charm sector in the quenched approximation, we analyze the second and fourth order cumulants of charm fluctuations and the correlations of charm with lighter conserved flavor quantum numbers. We can make use of a factor 100 larger statistics on ${N_τ=8}$ lattices which never have been used in studies of charm fluctuations. Analyzing correlations of charm fluctuations with baryon number and electric charge fluctuations we can project onto charmed baryon and meson correlations and compare results with quark model extended hadron resonance gas model calculations. We aim at a precise determination of the dissociation temperature of charmed hadrons and will probe the sensitivity of the fluctuations observables to the presence of multiple-charmed baryons.

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arXiv2022

The Chiral Phase Transition in three-flavor QCD from Lattice QCD

We analyze the pseudo-critical behavior of three-flavor QCD using highly improved staggered quarks (HISQ) on lattices with temporal extent $N_τ=8$ and for quark masses corresponding to a pseudoscalar Goldstone mass in the range $80 ~ {\rm MeV} ~ \lesssim ~ m_π~ \lesssim ~ 140 ~ {\rm MeV}$. Our findings are consistent with the occurrence of a second order chiral phase transition at vanishing values of the quark masses. The chiral phase transition temperature at this finite value of the lattice spacing is determined to be $T_c = 98_{-6}^{+3}~{\rm MeV}$. A comparison with a corresponding analysis performed in (2+1)-flavor QCD suggests that the continuum limit extrapolated chiral phase transition temperature in 3-flavor QCD will turn out to be below $90 ~ {\rm MeV}$.

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