Electric Charge Fluctuations Research Articles

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, [Formula: see text], the thermodynamics of charm can be very well understood in terms of charmed hadrons. We present evidence that above [Formula: see text], 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[Formula: see text]MeV, charmed hadron-like excitations significantly contribute to the partial charm pressure.

Coupled baryon, electric charge and strangeness fluctuations in heavy-ion collisions

We present for the first time quantitative results for the coupled dynamics of second order fluctuations in the three conserved charges of QCD based on stochastic diffusion equations for a Bjorken-type expanding hadronic medium. We show that the fluctuations deviate from local equilibrium expectations which can result in important phenomenological consequences for the interpretation of experimental data.

Critical point and Bose-Einstein condensation in pion matter

The Bose-Einstein condensation and the liquid-gas first order phase transition are studied in the interacting pion matter. Two phenomenological models are used: the mean-field model and the hybrid model. Free model parameters are fixed by fitting the lattice QCD data on the pion Bose condensate density at zero temperature. In spite of some minor differences the two model demonstrate an identical qualitative and very close quantitative behavior for the thermodynamic functions and electric charge fluctuations. A peculiar property of the considered models is an intersection of the Bose-Einstein condensation line and the line of the first order phase transition at the critical end point.

Phase diagram of interacting pion matter and isospin charge fluctuations

Equation of state and electric (isospin) charge fluctuations are studied for matter composed of interacting pions. The pion matter is described by self interacting scalar fields via a $\phi^4-\phi^6$ type Lagrangian. The mean-field approximation is used, and interaction parameters are fixed by fitting lattice QCD results on the isospin density as a function of the isospin chemical potential at zero temperature. Two scenarios for fixing the model parameters -- with and without the first order phase transition -- are considered, both yielding a satisfactory description of the lattice data. Thermodynamic functions and isospin charge fluctuations are studied and systematically compared for these two scenarios, yielding qualitative differences in the behavior of isospin charge susceptibilities. These differences can be probed by lattice simulations at temperatures $T \lesssim 100$ MeV.

Higher Order Cumulants of Electric Charge and Strangeness Fluctuations on the Crossover Line

We present lattice QCD calculations of higher order cumulants of electric charge distributions for small baryon chemical potentials $\mu_B$ by using up to NNNLO Taylor expansions. Ratios of these cumulants are evaluated on the pseudo-critical line, $T_{pc}(\mu_B)$, of the chiral transition and compared to corresponding measurements in heavy ion collision experiments by the STAR and PHENIX Collaborations. We demonstrate that these comparisons give strong constraints on freeze-out parameters. Furthermore, we use strangeness fluctuation observables to compute the ratio $\mu_S/\mu_B$ on the crossover line and compare it to $\mu_S/\mu_B$ at freeze-out stemming from fits to strange baryon yields measured by the STAR Collaboration.

Charge conservation and higher moments of charge fluctuations

Higher moments of distributions of net charge and baryon number in heavy-ion collisions have been proposed as signals of fundamental QCD phase transitions. In order to better understand background processes for these observables, models are presented which enable one to gauge the effects of local charge conservation, decays of resonances and clusters, Bose symmetrization, and volume fluctuations. Monte Carlo methods for generating samplings of particles consistent with local charge conservation are presented, and are followed by a review of simple analytic models involving a single type of charge with a constant experimental efficiency. The main model consists of thermal emission superimposed onto a simple parameterization of collective flow, known as a blast-wave, with emission being consistent with individual canonical ensembles. The spatial extent of local charge conservation is parameterized by the size and extent over which charge is conserved. The sensitivity of third and fourth order moments, skewness and kurtosis, to these parameters, and to beam energy and baryon density is explored. Comparisons with STAR data show that a significant part of the observed non-Poissonian fluctuations in net-proton fluctuations are explained by charge and baryon-number conservation, but that measurements of the STAR collaboration for fluctuations of net electric charge significantly differ from expectations of the models presented here.

Calculating fluctuations and self-correlations numerically for causal charge diffusion in relativistic heavy-ion collisions

We study the propagation and diffusion of electric charge fluctuations in the Bjorken hydrodynamic model with both white and Catteneo noise using purely numerical methods. We show that a global lattice of noise fluctuations is required to fully calculate the two-point correlators of charge. We solve the stochastic differential equations that arise from the charge conservation equation on the lattice. We explicitly identify the self-correlation term in the case of Catteneo noise and provide a physical interpretation. We provide a numerical recipe to remove this contribution from the full two-point correlators. Finally, we calculate the balance functions for charged hadrons. By limiting the speed of signal propagation, we observe the expected narrowing of the balance functions after removing the self-correlations.

Quark-diquark models and baryonic fluctuations in QCD

We study the baryonic fluctuations of electric charge, baryon number and strangeness, by considering a realization of the Hadron Resonance Gas model in the light flavor sector of QCD. We elaborate on the idea that the susceptibilities can be saturated with excited baryonic states with a quark-diquark structure with a linearly confining interaction identical up to a constant to the quark-antiquark potential, VqD′(r)=Vqq‾′(r). We obtain an overall good agreement with the spectrum obtained with other quark models and with lattice data for the fluctuations.

Baryonic susceptibilities, quark-diquark models, and quark-hadron duality at finite temperature

Fluctuations of conserved charges such as baryon number, electric charge and strangeness may provide a test for completeness of states in lattice QCD for three light flavors. We elaborate on the idea that the corresponding susceptibilities can be saturated with excited baryonic states with an underlying quark-diquark structure with a linearly confining interaction. Using Polyakov-loop correlators we show that in the static limit, the quark-diquark potential coincides with the quark-antiquark potential in marked agreement with recent lattice studies. We thus study in a quark-diquark model the baryonic fluctuations of electric charge, baryon number and strangeness: $\chi_{BQ}$, $\chi_{BB}$ and $\chi_{BS}$; by considering a realization of the hadron resonance gas model in the light flavor sector of QCD. These results have been obtained by using the baryon spectrum computed within a relativistic quark-diquark model, leading to an overall good agreement with the spectrum obtained with other quark models and with lattice data for the fluctuations.

Thermal fluctuations and correlations among hairs of a stable quantum black hole: Some examples

We have already derived the criteria for thermal stability of charged rotating quantum black holes, for horizon areas that are large relative to the Planck area. The derivation is done by using results of loop quantum gravity and equilibrium statistical mechanics of the grand canonical ensemble. We have also showed that in four-dimensional spacetime, quantum AdS Kerr–Newman black hole and asymptotically AdS dyonic black hole with electric and magnetic charge are thermally stable within certain range of its parameters. In this paper, the expectation values of fluctuations and correlations among horizon area, electric charge and angular momentum (magnetic charge) of these black holes are calculated within their range of stability. Interestingly, it is found that leading order fluctuations of electric charge and angular momentum (magnetic charge), in large horizon area limit, are independent of the values of electric charge and angular momentum (magnetic charge) at equilibrium.

Lattice thermodynamics at finite chemical potential from analytical Continuation

An efficient way to study the QCD phase diagram at small finite density is to extrapolate thermodynamical observables from imaginary chemical potential. We present results for fluctuations of baryon number to order (μB/T)6. The results at real chemical potentials are obtained through analytical continuation of simulations at imaginary chemical potentials. We also calculate higher order fluctuations of strangeness and electric charge to obtain the Taylor coefficients of the baryon number fluctuation with vanishing strangeness. We compare to the STAR proton fluctuation data to characterize the chemical freeze-out in view of the lattice results.

Causal electric charge diffusion and balance functions in relativistic heavy-ion collisions

We study the propagation and diffusion of electric charge fluctuations in high-energy heavy-ion collisions using the Cattaneo form for the dissipative part of the electric current. As opposed to the ordinary diffusion equation this form limits the speed at which charge can propagate. Including the noise term in the current, which arises uniquely from the fluctuation-dissipation theorem, we calculate the balance functions for charged hadrons in a simple 1+1-dimensional Bjorken hydrodynamical model. Limiting the speed of propagation of charge fluctuations increases the height and reduces the width of these balance functions when plotted versus rapidity. We also estimate the numerical value of the associated diffusion time constant from anti--de Sitter-space/conformal-field theory.

Screened van der Waals correction to density functional theory for solids

The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation to the exchange-correlation energy is widely used in materials science. For many solids it somewhat overestimates lattice constants and underestimates cohesive energies. What attraction among the ions is missing in PBE? For ionic solids and heavy metals, a detailed analysis shows that the answer is the van der Waals (vdW) interaction arising from electric charge fluctuations on different ions. Our vdW correction to PBE is a short-range damped and long-range screened pairwise interaction among the ions. We find that the three-body interactions are small due to screening, and that the vdW correction stabilizes the bcc structure of cesium halides over the rocksalt structure.

Magnetic Shift of the Chemical Freezeout and Electric Charge Fluctuations

Magnetic Shift of the Chemical Freezeout and Electric Charge Fluctuations

Magnetic Shift of the Chemical Freeze-out and Electric Charge Fluctuations.

We discuss the effect of a strong magnetic field on the chemical freeze-out points in ultrarelativistic heavy-ion collisions. As a result of inverse magnetic catalysis or magnetic inhibition, the crossover onset to hot and dense matter out of quarks and gluons should be shifted to a lower temperature. To quantify this shift we employ the hadron resonance gas model and an empirical condition for the chemical freeze-out. We point out that the charged particle abundances are significantly affected by the magnetic field so that the electric charge fluctuation is largely enhanced, especially at high baryon density. The charge conservation partially cancels the enhancement, but our calculation shows that the electric charge fluctuation could serve as a magnetometer. We find that the fluctuation exhibits a crossover behavior rapidly increased for eB≳(0.4 GeV)^{2}, while the charge chemical potential has smoother behavior with an increasing magnetic field.

Exploring effects of magnetic field on the hadron resonance gas

We present a study of the effects of magnetic fields on fluctuations and correlations in the hadron resonance gas model. We find significant changes in the fluctuations of net baryon number, electric charge and strangeness. This is also reflected in various fluctuation ratios along the freezeout curve.

The weak bound state with the non-zero charge density as the LHC 126.5 GeV state

The self-consistent model of classical field interactions formulated as the counterpart of the quantum electroweak model leads to homogeneous boson ground state solutions in presence of non-zero extended fermionic charge density fluctuations. Two different types of electroweak configurations of fields are analyzed. The first one has non-zero electric and weak charge fluctuations. The second one is electrically uncharged but weakly charged. Both types of configurations have two physically interesting solutions which possess masses equal to 126.67 GeV at the value of the scalar fluctuation potential parameter $\lambda$ equal to ~ 0.0652. The spin zero electrically uncharged droplet formed as a result of the decay of the charged one is interpreted as the ~ 126.5 GeV state found in the Large Hadron Collider (LHC) experiment. (The other two configurations correspond to solutions with masses equal to 123.7 GeV and $\lambda$ equal to ~ 0.0498 and thus the algebraic mean of the masses of two central solutions, i.e., 126.67 GeV and 123.7 GeV, is equal to 125.185 GeV.) The problem of a mass of this kind of droplets will be considered on the basis of the phenomenon of the screening of the fluctuation of charges. Their masses are found in the thin wall approximation.

The charged inflaton and its gauge fields: preheating and initial conditions for reheating

We calculate particle production during inflation and in the early stages of reheating after inflation in models with a charged scalar field coupled to Abelian and non-Abelian gauge fields. A detailed analysis of the power spectra of primordial electric fields, magnetic fields and charge fluctuations at the end of inflation and preheating is provided. We carefully account for the Gauss constraints during inflation and preheating, and clarify the role of the longitudinal components of the electric field. We calculate the timescale for the back-reaction of the produced gauge fields on the inflaton condensate, marking the onset of non-linear evolution of the fields. We provide a prescription for initial conditions for lattice simulations necessary to capture the subsequent nonlinear dynamics. On the observational side, we find that the primordial magnetic fields generated are too small to explain the origin of magnetic fields on galactic scales and the charge fluctuations are well within observational bounds for the models considered in this paper.

Effects of kinematic cuts on net electric charge fluctuations

The effects of kinematic cuts on electric charge fluctuations in a gas of charged particles are discussed. We consider a very transparent example of an ideal pion gas with quantum statistics, which can be viewed as a multi-component gas of Boltzmann particles with different charges and masses. Cumulants of net-electric charge fluctuations $\chi_n^Q$ are calculated in a static and expanding medium with flow parameters adjusted to the experimental data. We show that the transverse momentum cut, $p_{t_\text{min}}\leq p_t\leq p_{t_\text{max}}$, weakens the effects of Bose statistics, i.e. contributions of effectively multi-charged states to higher order moments. Consequently, cuts in $p_t$ modify the experimentally measured cumulants and their ratios. We discuss the influence of kinematic cuts on the ratio of mean and variance of electric charge fluctuations in a hadron resonance gas, in the light of recent data of the STAR and PHENIX Collaborations. We find that the different momentum cuts of $p_{t_\text{min}}=0.2$~GeV (STAR) and $p_{t_\text{min}}=0.3$~GeV (PHENIX) are responsible for more than 30\% of the difference between these two data sets. We argue that the $p_t$ cuts imposed on charged particles will influence the normalized kurtosis {$\kappa_Q\sigma_Q^2 = \chi_4^Q/\chi_2^Q$} of the electric charge fluctuations. In particular, the reduction of $\kappa_Q\sigma_Q^2$ with increasing $p_{t_\text{min}}$ will lead to differences between PHENIX and STAR data of ${\cal O}(6\%)$ which currently are buried under large statistical and systematic errors. We furthermore introduce the relation between momentum cut-off and finite volume effects, which is of relevance for the comparison between experimental data and lattice QCD calculations.

Recent results from high temperature lattice QCD

Recent results obtained from numerical computations in lattice regularized QCD are summarized. The write-up of the talk concentrates on the liberation of strange quarks in the vicinity of the chiral QCD transition and on certain ratios of cumulants of net electric charge fluctuations which can be used to determine freeze-out parameters by a comparison of experimental data from heavy ion collisions with lattice QCD results.