arXiv subjects

Igor Mishustin

Publications and source records attributed to Igor Mishustin.

At least 37 records · Page 2Linked to original sources

arXiv2013

Chiral fluid dynamics with explicit propagation of the Polyakov loop

We present a fully dynamical model to study nonequilibrium effects in both the chiral and the deconfinement phase transition. The sigma field and the Polyakov loop as the corresponding order parameters are propagated by Langevin equations of motion. The locally thermalized background is provided by a fluid of quarks and antiquarks. Allowing for an exchange of energy and momentum through dissipative and stochastic processes we ensure that the total energy of the coupled system remains conserved. We study its relaxational dynamics in different quench scenarios and are able to observe critical slowing down as well as the enhancement of long wavelength modes at the critical point. During the fluid dynamical expansion of a hot plasma fireball typical nonequilibrium effects like supercooling and domain formation occur when the system evolves through the first order phase transition.

nucl-th↗

arXiv2011

The phase structure of a chiral model with dilatons in hot and dense matter

We explore the phase structure of a chiral model of constituent quarks and gluons implementing scale symmetry breaking at finite temperature and chemical potential. In this model the chiral dynamics is intimately linked to the trace anomaly saturated by a dilaton field. The thermodynamics is governed by two condensates, thermal expectation values of sigma and dilaton fields, which are the order parameters responsible for the phase transitions associated with the chiral and scale symmetries. Within the mean field approximation, we find that increasing temperature a system experiences a chiral phase transition and then a first-order phase transition of partial scale symmetry restoration characterized by a melting gluon-condensate takes place at a higher temperature. There exists a region at finite chemical potential where the scale symmetry remains dynamically broken while the chiral symmetry is restored. We also give a brief discussion on the sigma-meson mass constrained from Lattice QCD.

hep-ph↗

arXiv2011

The phase diagram in $T-μ-N_c$ space

We examine the phase diagram of hadronic matter when the number of colors, as well as temperature and density, are varied. We show that in this regime several new phase transitions are possible, and we examine issues related to these transitions.

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arXiv2011

The impact of dissipation and noise on fluctuations in chiral fluid dynamics

We investigate the nonequilibrium evolution of the sigma field coupled to a fluid dynamic expansion of a hot fireball to model the chiral phase transition in heavy-ion collisions. The dissipative processes and fluctuations are allowed under the assumption that the total energy of the coupled system is conserved. We use the linear sigma model with constituent quarks to investigate the effects of the chiral phase transition on the equilibration and excitation of the sigma modes. The quark fluid acts as a heat bath in local thermal equilibrium and the sigma field evolves according to a semiclassical stochastic Langevin equation of motion. The effects of supercooling and reheating in a first order phase transition are observed when the sigma field relaxes to equilibrium with the quark fluid. Nonequilibrium fluctuations at the first order phase transition lead to an increase in the intensity of sigma fluctuations in comparison to a scenario with a critical point.

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arXiv2010

How large is "large $N_c$" for Nuclear matter?

We argue that a so far neglected dimensionless scale, the number of neighbors in a closely packed system, is relevant for the convergence of the large $N_c$ expansion at high chemical potential. It is only when the number of colors is large w.r.t. this new scale ($\sim \order{10}$) that a convergent large $N_c$ limit is reached. This provides an explanation as to why the large $N_c$ expansion, qualitatively successful in in vacuum QCD, fails to describe high baryo-chemical potential systems, such as nuclear matter. It also means that phenomenological claims about high density matter based on large $N_c$ extrapolations should be treated with caution.

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arXiv2010

The nuclear liquid-gas phase transition at large $N_c$ in the Van der Waals approximation

We examine the nuclear liquid-gas phase transition at large number of colors ($N_c$) within the framework of the Van Der Waals (VdW) model. We argue that the VdW equation is appropriate at describing inter-nucleon forces, and discuss how each parameter scales with $N_c$. We demonstrate that $N_c=3$ (our world) is not large with respect to the other dimensionless scale relevant to baryonic matter, the number of neighbors in a dense system $N_N$. Consequently, we show that the liquid-gas phase transition looks dramatically different at $N_c \to \infty$ with respect of our world: The critical point temperature becomes of the order of $\lqcd$ rather than below it. The critical point density becomes of the order of the baryonic density, rather than an order of magnitude below it. These are precisely the characteristics usually associated with the "Quarkyonic phase". We therefore conjecture that quarkyonic matter is simply the large $N_c$ limit of the nuclear liquid, and the interplay between $N_c$ and $N_N$ is the reason why the nuclear liquid in our world is so different from quarkyonic matter. We conclude by suggesting ways our conjecture can be tested in future lattice measurements.

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arXiv2010

On possibility of synthesizing superheavy elements in nuclear explosions

The possibility to produce superheavy elements in the course of low-yield nuclear explosions is analyzed within a simple kinetic model which includes neutron capture, gamma-emission, fission and particle evaporation from excited nuclei. We have calculated average numbers of absorbed neutrons as well as mass distributions of U and Cm nuclei exposed to an impulsive neutron flux, as functions of its duration. It is demonstrated that detectable amounts of heavy nuclei absorbing from 20 to 60 neutrons may be produced in this process. According to an optimistic scenario, after multiple beta-decay such nuclei may reach the long-living elements of the predicted ``island of stability''.

nucl-th↗

arXiv2010

Thermodynamics of dense hadronic matter in a parity doublet model

We study thermodynamics of nuclear matter in a two-flavored parity doublet model within the mean field approximation. Parameters of the model are chosen to reproduce correctly the properties of the nuclear ground state. The model predicts two phase transitions in nuclear matter, a liquid-gas phase transition at normal nuclear density and a chiral transition at higher density. At finite temperature the pion decay constant exhibits a considerable reduction at intermediate values of chemical potential, which is traced back to the presence of the liquid-gas transition, and approaches zero at higher chemical potential associated with the chiral symmetry restoration. A "transition" from meson-rich to baryon-rich matter is also discussed.

hep-ph↗

arXiv2009

Nuclear fragmentation reactions in extended media studied with Geant4 toolkit

It is well known from numerous experiments that nuclear multifragmentation is a dominating mechanism for production of intermediate-mass fragments in nucleus-nucleus collisions at energies above 100 A MeV. In this paper we investigate the validity and performance of the Fermi break-up model and the statistical multifragmentation model implemented as parts of the Geant4 toolkit. We study the impact of violent nuclear disintegration reactions on the depth-dose profiles and yields of secondary fragments for beams of light and medium-weight nuclei propagating in extended media. Implications for ion-beam cancer therapy and shielding from cosmic radiation are discussed.

physics.med-ph↗

arXiv2009

Universality of the Diffusion Wake from Stopped and Punch-Through Jets in Heavy-Ion Collisions

We solve (3+1)-dimensional ideal hydrodynamical equations with source terms that describe punch-through and fully stopped jets in order to compare their final away-side angular correlations in a static medium. For fully stopped jets, the backreaction of the medium is described by a simple Bethe-Bloch-like model which leads to an explosive burst of energy and momentum (Bragg peak) close to the end of the jet's evolution through the medium. Surprisingly enough, we find that the medium's response and the corresponding away-side angular correlations are largely insensitive to whether the jet punches through or stops inside the medium. This result is also independent of whether momentum deposition is longitudinal (as generally occurs in pQCD energy loss models) or transverse (as the Bethe-Bloch formula implies). The existence of the diffusion wake is therefore shown to be universal to all scenarios where momentum as well as energy is deposited into the medium, which can readily be understood in ideal hydrodynamics through vorticity conservation. The particle yield coming from the strong forward moving diffusion wake that is formed in the wake of both punch-through and stopped jets largely overwhelms their weak Mach cone signal after freeze-out.

nucl-th↗

arXiv2009

Bulk viscosity-driven freeze-out in heavy ion collisions

We give an review the HBT puzzle, and argue that its resolution requires the introduction of new physics close to the phase transition scale. We argue that a candidate for this new physics is bulk viscosity, recently postulated to peak, and even diverge, close to the phase transition temperature. We show that such a viscosity peak can force the system created in heavy ion collisions to become unstable, and filament into fragments whose size is weakly dependent on the global size of the system, thereby triggering freeze-out.

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arXiv2008

Physics of ion beam cancer therapy: a multi-scale approach

We propose a multi-scale approach to understand the physics related to ion-beam cancer therapy. It allows the calculation of the probability of DNA damage as a result of irradiation of tissues with energetic ions, up to 430 MeV/u. This approach covers different scales, starting from the large scale, defined by the ion stopping, followed by a smaller scale, defined by secondary electrons and radicals, and ending with the shortest scale, defined by interactions of secondaries with the DNA. We present calculations of the probabilities of single and double strand breaks of DNA, suggest a way to further expand such calculations, and also make some estimates for glial cells exposed to radiation.

physics.bio-ph↗

arXiv2008

Instability of Boost-invariant hydrodynamics with a QCD inspired bulk viscosity

We solve the relativistic Navier-Stokes equations with homogeneous boost-invariant boundary conditions, and perform a stability analysis of the solution. We show that, if the bulk viscosity has a peak around $T_c$ as inferred from QCD-based arguments, the background solution "freezes" at $T_c$ to a nearly constant temperature state. This state is however highly unstable with respect to certain inhomogeneous modes. Calculations show that these modes have enough time to blow up and tear the system into droplets. We conjecture that this is how freeze-out occurs in the QGP created in heavy ion collisions, and perhaps similar transitions in the early universe.

hep-ph↗

arXiv2008

Ion-beam therapy: from electron production in tissue like media to DNA damage estimations

Radiation damage induced by ion beams is traditionally treated at different levels of theoretical approaches, for the different scales and mechanisms involved.We present here details of a combined approach that, from a method at a nanoscopic scale, attempts to merge with higher scales existing results, by tuning the analytical method employed when extended to larger scale and so yielding a consistent picture of the entire process. Results will show the possibility to get a good agreement with macroscale methods and, on the other hand, to produce a reliable electron energy spectra to be used for DNA damage estimations.

physics.bio-ph↗

arXiv2008

Freeze-out by bulk viscosity driven instabilities

We describe a new scenario (first introduced in [G. Torrieri, B. Tomášik and I. Mishustin, Phys. Rev. C \textbf{77}, 034903 (2008)]) for freezeout in heavy ion collisions that could solve the lingering problems associated with the so-called HBT puzzle. We argue that bulk viscosity increases as $T$ approaches $T_c$. The fluid {then} becomes unstable against small perturbations, and fragments into clusters of a size much smaller than the total size of the system. These clusters maintain the pre-existing outward-going flow, as a spray of droplets, but develop no flow of their own, and hadronize by evaporation. We show that this scenario can explain HBT data and suggest how it can be experimentally tested.

hep-ph↗

arXiv2008

Bulk Viscosity driven clusterization of quark-gluon plasma and early freeze-out in relativistic heavy-ion collisions

We introduce a new scenario for heavy ion collisions that could solve the lingering problems associated with the so-called HBT puzzle. We postulate that the system starts expansion as the perfect quark-gluon fluid but close to freeze-out it splits into clusters, due to a sharp rise of bulk viscosity in the vicinity of the hadronization transition. We then argue that the characteristic cluster size is determined by the viscosity coefficient and the expansion rate. Typically it is much smaller and independent of the total system volume. These clusters maintain the pre-existing outward-going flow, as a spray of droplets, but develop no flow of their own, and hadronize by evaporation. We provide an ansatz for converting the hydrodynamic output into clusters.

nucl-th↗

arXiv2007

Fragmentation of the fireball and how to observe it

We argue that fragmentation at hadronisation is likely scenario in ultrarelativistic nuclear collisions. In case of crossover phase transition it is driven by a singularity of the bulk viscosity. We claim that such a scenario can explain the ``HBT puzzle'' and can be identified by non-statistical differences between event-wise rapidity distributions and by proton-proton rapidity correlations.

nucl-th↗

arXiv2007

PET monitoring of cancer therapy with He-3 and C-12 beams: a study with the GEANT4 toolkit

We study the spatial distributions of $β^+$-activity produced by therapeutic beams of $^3$He and $^{12}$C ions in various tissue-like materials. The calculations were performed within a Monte Carlo model for Heavy-Ion Therapy (MCHIT) based on the GEANT4 toolkit. The contributions from $^{10,11}$C, $^{13}$N, $^{14,15}$O, $^{17,18}$F and $^{30}$P positron-emitting nuclei were calculated and compared with experimental data obtained during and after irradiation. Positron emitting nuclei are created by $^{12}$C beam in fragmentation reactions of projectile and target nuclei. This leads to a $β^+$-activity profile characterised by a noticeable peak located close to the Bragg peak in the corresponding depth-dose distribution. On the contrary, as the most of positron-emitting nuclei are produced by $^3$He beam in target fragmentation reactions, the calculated total $β^+$-activity during or soon after the irradiation period is evenly distributed within the projectile range. However, we predict also the presence of $^{13}$N, $^{14}$O, $^{17,18}$F created in charge-transfer reactions by low-energy $^3$He ions close to the end of their range in several tissue-like media. The time evolution of $β^+$-activity profiles was investigated for both kinds of beams. Due to the production of $^{18}$F nuclide the $β^+$-activity profile measured 2 or 3 hours after irradiation with $^{3}$He ions will have a distinct peak correlated with the maximum of depth-dose distribution. We found certain advantages of low-energy $^{3}$He beams over low-energy proton beams for reliable PET monitoring during particle therapy of shallow located tumours. In this case the distal edge of $β^+$-activity distribution from $^{17}$F nuclei clearly marks the range of $^{3}$He in tissues.

physics.med-ph↗