arXiv subjects

E. V. Shuryak

Publications and source records attributed to E. V. Shuryak.

At least 19 recordsLinked to original sources

arXiv2007

On the Origin of the "Ridge" phenomenon induced by Jets in Heavy Ion Collisions

We argue that "ridge" in 2-particle correlation function associated with hard trigger at RHIC heavy ion collisions is naturally explained by an interrelation of jet quenching and hydrodynamical transverse flow. The excess particles forming the ridge are produced by QCD bremsstrahlung along the beam (and thus have wide rapidity distribution) and then boosted by transverse flow. Nontrivial correlation between directions of the jet and the radial flow is provided by jet quenching: our straightforward and basically parameter-independent calculation reproduces the angular shape, width and other properties of the "ridge".

nucl-th↗

arXiv2007

Influence of Meson's Widths on Yukawa-like Potentials and Lattice Correlation Functions

Euclidean point-to-point propagators or wall-to-wall correlators related to exchange by an unstable particle(sigma,rho,omega-mesons) are modified by presence of particle width. In particular, the usual method of deriving particle masses from logarithmic derivatives need to be modified. Similarly Yukawa-like potentials of nuclear physics due to exchange of those mesons are significantly modified since the coupling to the decay products is strong. For example, the large distance asymptotic changes, exp(-M_{min} r), where M_{min} is the sum of the decay product masses (2 m_π, 2 m_{e}, 2 m_ν). In the area M_{min}r<1the potential has a long-range tail 1/r^3. Similar effects appear due to the virtual decays in the elecroweak sector of the Standard model. The $Z-γ$ mixing via electron loop gives the parity violation potential with the range $1/2 m_{e}$, i.e. the range of the weak interaction increases $10^{5}$ times.

nucl-th↗

arXiv2007

How changing physical constants and violation of local position invariance may occur?

Light scalar fields very naturally appear in modern cosmological models, affecting such parameters of Standard Model as electromagnetic fine structure constant $α$, dimensionless ratios of electron or quark mass to the QCD scale, $m_{e,q}/Λ_{QCD}$. Cosmological variations of these scalar fields should occur because of drastic changes of matter composition in Universe: the latest such event is rather recent (redshift $z\sim 0.5$), from matter to dark energy domination. In a two-brane model (we use as a pedagogical example) these modifications are due to changing distance to "the second brane", a massive companion of "our brane". Back from extra dimensions, massive bodies (stars or galaxies) can also affect physical constants. They have large scalar charge $Q_d$ proportional to number of particles which produces a Coulomb-like scalar field $ϕ=Q_d/r$. This leads to a variation of the fundamental constants proportional to the gravitational potential, e.g. $δα/ α= k_αδ(GM/ r c^2)$. We compare different manifestations of this effect. The strongest limits $k_α+0.17 k_e= (-3.5\pm 6) * 10^{-7}$ are obtained from the measurements of dependence of atomic frequencies on the distance from Sun (the distance varies due to the ellipticity of the Earth's orbit).

physics.atom-ph↗

arXiv2006

Strongly Coupled Quark-Gluon Plasma: The Status Report

RHIC data have shown robust collective flows, strong jet and charm quenching, and charm flow. Recently ``conical flows'' from damped jets were seen. Non-Abelian classical strongly coupled plasmas were introduced and studied via molecular dynamics, with first results for its transport (diffusion and viscosity) reported. Quantum-mechanical studies reveal the survival for $T>T_c$ of the lowest binary states, including colored ones, and also of some manybody ones such as baryons. ``Polymeric chains'' $\bar q.g.g... q$ are also bound in some range of $T$, perhaps the progenitors of the QCD strings. AdS/CFT applications advanced to a completely new level of detail: they now include studies of thermal heavy quark motion, jet quenching and even conical flow. Confinement is however still beyond simply strong coupling: its de-facto inclusion the so called AdS/QCD approach is so far added as a model, while true understanding may probably only come from further insights into the monopole dynamics.

hep-ph↗

arXiv2006

Locating strongly coupled color superconductivity using universality and experiments with trapped ultracold atoms

Cold fermionic atoms are known to enter the universal strongly coupled regime as their scattering length $a$ gets large compared to the inter-particle distances. Recent experimental data provide important critical parameters of such system. We argue that quarks may enter the same regime due to marginal binding of diquarks, and if so one can use its universality in order to deduce such properties as the slope of the critical line of color superconductivity, $dT_c/dμ$. We further discuss limitations on the critical temperature itself and conclude that it is limited by $T_c<70\, MeV$.

nucl-th↗

arXiv2006

Hydrodynamic Flow from Fast Particles

We study the interaction of a fast moving particle in the Quark Gluon Plasma with linearized hydrodynamics. We derive the linearized hydrodynamic equations on top of an expanding fireball, and detail the solutions for a static medium. There are two modes far from the jet -- a sound mode and a diffusion mode. The diffusion mode is localized in a narrow wake behind the jet while the sound mode propagates at the Mach angle, $\cos(θ_M) = c_s/c$. A general argument shows that the strength of the diffusion mode relative to the sound mode is directly proportional to the entropy produced by the jet-medium interaction. This argument does not rely on the linearized approximation and the assumption of local thermal equilibrium close to the jet. With this insight we calculate the spectrum of secondaries associated with the fast moving particle. If the energy loss is large and the jet-medium interaction does not produce significant entropy, the flow at the Mach angle can be observed in the associated spectrum. However, the shape of associated spectra is quite fragile and sensitive to many of the inputs of the calculation.

hep-ph↗

arXiv2006

Possible evidence for "dark radiation" from Big Bang Nucleosynthesis Data

We address the emerging discrepancy between the Big Bang Nucleosynthesis data and standard cosmology, which asks for a bit longer evolution time. If this effect is real, one possible implication (in a framework of brane cosmology model) is that there is a ``dark radiation'' component which is negative and makes few percents of ordinary matter density. If so, all scales of this model can be fixed, provided brane-to-bulk leakage problem is solved.

hep-th↗

arXiv2005

Conical flow in a medium with variable speed of sound

In high energy nuclear collisions, QCD jets deposit a large fraction of their energy into the produced matter. It has been proposed that as such matter behaves as a liquid with a very small viscosity, a fraction of this energy goes into a collective excitation called the ``conical flow'', similar e.g. to the sonic booms generated by the supersonic planes. In this work we study the effect of time-dependent speed of sound on the development of the conical wave. We show that the expansion of matter and the decrease of $c_s$ leads to an increase of observable manifestations of the conical flow. We also show that if the QCD phase transition is of the first order (and thus with vanishing speed of sound in the mixed phase) the wave must split into two, with opposite directions. We then argue that it is not the case experimentally, which supports the conclusion that the QCD phase transition is $not$ of the first order.

hep-ph↗

arXiv2005

Conical Flow induced by Quenched QCD Jets

Quenching is a recently discovered phenomenon in which QCD jets created in heavy ion collisions deposit a large fraction or even all their energy and momentum into the produced matter. At RHIC and higher energies, where that matter is a strongly coupled Quark-Gluon Plasma (sQGP) with very small viscosity, we suggest that this energy/momentum propagate as a collective excitation or ``conical flow''. Similar hydrodynamical phenomena are well known, e.g. the so called sonic booms from supersonic planes. We solve the linearized relativistic hydrodynamic equations to detail the flow picture. We argue that for RHIC collisions the direction of this flow should make a cone at a specific large angle with the jet, of about $70^o$, and thus lead to peaks in particle correlations at the angle $Δϕ=π\pm 1.2$ rad relative to the large-$p_t$ trigger. This angle happens to matchperfectly the position of the maximum in the angular distribution of secondaries associated with the trigger recently seen by the STAR and PHENIX collaborations. We also discuss briefly possible alternative explanations and suggest some further tests to clarify the mechanism.

hep-ph↗

arXiv2005

Toward dynamical understanding of the diquarks, pentaquarks and dibaryons

QCD instantons are known to produce deeply bound diquarks. We study whether it may be used as building blocks in the formation of multiquark states, in particular pentaquarks and dibaryons. A simple model is presented in which the lowest scalar diquark (and possibly the tensor one) can be treated as an independent ``body'', with the same color and (approximately) the same mass as a constituent (anti)quark. In it a new symmetry exists between states with the same number of ``bodies'' but different number of quarks appear, in particular the 3-``body'' pentaquarks can be naturally related to some excited baryons. The limitations of this model are seen from the fact that it leads to light dibaryon $H$. Another reported work is based on a calculation of a large set of correlation functions for nonlocal operators with 4 to 6 light quarks in the Random Instanton Liquid Model (RILM). The effective interaction between diquarks is studied and found to posses a strongly {\em repulsive core}, due to the Pauli principle for quark zero modes.

hep-ph↗

arXiv2004

Instantons, diquarks and non-leptonic weak decays of hyperons

This work is devoted to the study of the non-perturbative contributions in non-leptonic hyperon decays. We show that the instanton-induced 't Hooft interaction can naturally explain the Delta I=1/2 rule, by generating quark-diquark clustering inside octet baryons. We compute P-wave and S-wave amplitudes in the Instanton Liquid Model (ILM), and find good agreement with experiment. We propose a model-independent procedure to test on the lattice if the leading quark-quark attraction in the 0^+ anti-triplet channel responsible for diquark structures in hadrons is originated by the interaction generated by quasi-classical fields or it is predominantly due to other perturbative and/or confining forces.

hep-ph↗

arXiv2004

What RHIC Experiments and Theory tell us about Properties of Quark-Gluon Plasma ?

This brief review summarizes the main experimental discoveries made at RHIC and then discusses their implications. The robust collective flow phenomena are well described by ideal hydrodynamics, with the Equation of State (EoS) predicted by lattice simulations. However the transport properties turned out to be unexpected, with rescattering cross section one-to-two orders of magnitude larger than expected from perturbative QCD. These and other theoretical developments indicate that Quark-Gluon Plasma (QGP) produced at RHIC, and probably in a wider temperature region $T_c<T<4T_c$, is not at all a weakly coupled quasiparticle gas, but is rather in a strongly coupled regime, sQGP for short. After reviewing two other ``strongly coupled systems'', (i) the strongly coupled supersymmetric theories studied via Maldacena duality; (ii) trapped ultra-cold atoms with very large scattering length, we return to sQGP and show that there should exist literally hundreds of bound states in it in the RHIC domain, most them colored. We then discuss recent ideas of their effect on the EoS, viscosity and jet quenching.

hep-ph↗

arXiv2003

Instanton contribution to the pion and proton formfactors at Q^2 greater than 1 GeV^2

Studying the instanton-induced contributions to various hard exclusive reactions provides physical insight into the transition from the non-perturbative to the perturbative regime of QCD. To this end, we study the leading-instanton contribution to the electro-magnetic and transition formfactors, using an effective theory of the Instanton Liquid Model. We report predictions for the space-like electro-magnetic formfactor of the pion, as well as recent results for the Dirac formfactor of the proton.

hep-ph↗

arXiv2003

Jet fragmentation due to a quark/diquark pick-up in high energy heavy ion collisions

We propose a model aimed at explaining jet quenching, large azimuthal asymmetry and baryon/meson ratio at large transverse momenta pt=2-10 GeV observed at RHIC. Its main point is that a QCD string can be cut by matter quarks and/or diquarks before its natural breaking. We model the early quark/diquark production via QCD sphalerons.

hep-ph↗

arXiv2003

Freezeout of resonances and nuclear fragments at RHIC

We quantify the conditions at which ``composites'', the resonances and bound states $d,He^3$ are produced at RHIC. Using Hubble-like model for late stages, one can analytically solve the rate equations and also calculate the relevant optical depth factors. We calculate also the modification of $ρ$ masse and width, and predict a radiacal shape change of $σ$.

hep-ph↗

arXiv2003

D-Meson Production from Recombination in Hadronic Collisions

Nonperturbative effects in $D$-meson production in pion-nucleon and proton-nucleon collisions are investigated within the recombination model. The coalescence of perturbatively created charm quarks with sea- and valence-quarks from projectile and target fragments is shown to be competitive in magnitude with standard fragmentation calculations at both central (small $x_F$) and forward rapidities. Corresponding flavor asymmetries for inclusive $D$-meson production are thus mostly generated on the (light-) parton distribution level, and turn out to be in reasonable overall agreement with available fixed-target data. Predictions for upcoming measurements at RHIC are given.

hep-ph↗

arXiv2003

Dependence of hadronic properties on Quark Masses and Constraints on their Cosmological Variation

We follow our previous paper on possible cosmological variation of weak scale (quark masses) and strong scale, inspired by data on cosmological variation of the electromagnetic fine structure constant from distant quasar (QSO) absorption spectra. In this work we identify the {\em strange quark mass} $m_s$ as the most important quantity, and the {\em sigma meson mass} as the ingredient of the nuclear forces most sensitive to it. As a result, we claim significantly stronger limits on ratio of weak/strong scale ($W=m_s/Λ_{QCD}$) variation following from our previous discussion of primordial Big-Bang Nucleosynthesis ($|δW/W|<0.006$) and Oklo natural nuclear reactor ($|δW/W|<1.2 \cdot 10^{-10}$; there is also a non-zero solution $δW/W=(-0.56 \pm 0.05) \cdot 10^{-9}$) .

hep-ph↗

arXiv2002

Spontaneously Broken Chiral Symmetry and Hard QCD Phenomena

These are the mini-proceedings of the workshop ``Spontaneously Broken Chiral Symmetry and Hard QCD Phenomena" held at the Physikzentrum Bad Honnef from July 15 to 19, 2002. Every author presents a summary of his talk. The transparencies of all speakers and further information on the workshop can be found on the website: http://www.tp2.ruhr-uni-bochum.de/hardreactions.html

hep-ph↗