Theoretical outlook. D. Kharzeev

Transcription

1 High Energy Physics in the LHC Era, Valparaiso, Chile, 2012 QCD Workshop on Chirality, Vorticity, and Magnetic Field In Heavy Ion Collisions, UCLA, January 21-23, 2015 Theoretical outlook D. Kharzeev Supported by the Office of Science, US Department of Energy 1

2 Outline Chirality, magnetic field and heavy ion program Broad implications: nuclear, condensed matter, astrophysics, cosmology, and biology Current status Open problems, and how to approach them Disclaimer: not a summary talk! 2

3 Why do we do heavy ion physics? The goal: to achieve a better understanding of how QCD works. This will have broad implications for other fields of science. To get there, we need to build detectors and phenomenological models, but we should never lose the sight of ultimate goal. 3

4 Magnetic field as a probe of QCD Electromagnetic interactions (through Deep-Inelastic Scattering and e + e - annihilation) allowed to establish the existence of quarks and the QCD as the theory of strong interactions. Through the Bjorken scaling and deviations from it, the asymptotic freedom and the RG flow in QCD have been established. Parton distributions inside the proton as a function of Bjorken x; CTEQ Coll.

5 QCD in magnetic fields Later it has become clear that to understand QCD, we have to understand the properties of extended gluon field configurations, many of which have non-trivial topological contents. In DIS, these extended configurations in general yield power corrections to the cross section - not easy to decipher However an external coherent magnetic field is a perfect probe of the chiral quarks and thus of the topological gluon field configurations.

6 Topological number fluctuations in QCD vacuum ITEP Lattice Group 6

7 Numerical evidence for chiral magnetic effect in lattice gauge theory, P. Buividovich, M. Chernodub, E. Luschevskaya, M. Polikarpov, ArXiv ; PRD Red - positive charge Blue - negative charge SU(2) quenched, Q = 3; Electric charge density (H) - Electric charge density (H=0)

8 Arxiv:

9 Topology and confinement in QCD The instanton solutions in Minkowski space-time describe the tunneling events between the topological sectors of the vacuum marked by different integer values of N CS Z d 3 xk o Energy of gluon field N CS = instanton sphaleron 9

10 Can this periodic structure of the vacuum be linked to confinement? DK and E.Levin, arxiv: The periodic structure of the vacuum is encoded in Veneziano s ghost saturating the Ward identity for the topological current: This procedure introduces the coupling of the ghost to the gluons: this coupling modifies the gluon propagator! 10

11 Analogy to Bloch crystal The tunneling of quasiparticles through the crystalline lattice leads to a similar ghost in the correlation function: Diakonov, Eides Energy of gluon field even closer analogy if N CS = instanton sphaleron In perturbation theory, infinitely heavy electron! DK and E.Levin, arxiv:

12 Analogy to Bloch crystal In perturbation theory, infinitely heavy electron! in this limit, electrons in the crystal do not respond to photons. In QCD, this corresponds to the usual perturbation theory (the compact nature of SU(N) is ignored). However, at finite (non-zero susceptibility), the propagation of photons (gluons) is strongly affected by the crystalline lattice: DK and E.Levin, arxiv:

13 Topology as a cause of confinement? The Dyson-Schwinger equation for the gluon propagator: Solution: This is the Gribov propagator, proposed to solve the problem of gauge copies Complex poles at - confinement! Gluons cannot propagate at momenta smaller than DK and E.Levin, arxiv:

14 Gluon dressed by ghost loops: the glost Glost n. Glost adj: Glosty Glost is a multi-versatile word used to explain something positive or desirable, generally something that occurs between two close friends. Glost may be used in place of your best friends name, in a moment of happiness and excitement to see him/her. Glost may also be used in place of other words, particularly the word "love" or words that sound similar to Glost, such as "Lost" 14

15 The running QCD coupling Freezing (in YM) or vanishing (in QCD) in the IR running coupling 15 DK and E.Levin, arxiv:

16 Topology and spin physics: a link to the EIC program The use of glost propagator and ghost attachments in QCD amplitudes introduces spin asymmetries not present in pqcd an example of a direct connection between the studies of topology in heavy ion collisions, spin program at RHIC, and the future EIC program P-odd terms in fragmentation functions are allowed, and will contribute to correlations (P invariance: ) 16 Z.Kang, DK, PRL 11

17 CME in real life : BNL - Stony Brook - Princeton - Berkeley arxiv: [cond-mat.str-el] 17

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19 Put the crystal in parallel E, B fields the anomaly generates chiral charge: and thus the chiral chemical potential: 19

20 so that there is a chiral magnetic current: resulting in the quadratic dependence of CME conductivity on B: adding the Ohmic one negative magnetoresistance Son, Spivak,

21 21 big potential for applications!

22 The chirality of life Force of nature gave life its asymmetry 'Left-handed' electrons destroy certain organic molecules faster than their mirror versions. E. Gibney, Nature, 25 September 2014 Chirally Sensitive Electron-Induced Molecular Breakup and the Vester-Ulbricht Hypothesis Phys. Rev. Lett. 113, Published 12 September 2014 J. M. Dreiling and T. J. Gay

23 Symmetry as a guiding star Symmetry is the most important concept in modern physics Symmetries provide the guiding principle for constructing all known physical theories, both fundamental and the effective ones, including hydrodynamics 23

24 Progress in understanding of quantum fluids is one of the lasting achievements of RHIC program Two directions: Quantum bounds on conventional transport coefficients New transport coefficients of entirely quantum origin (CM conductivity etc) 24

25 Current status Experiment (talk by S.Voloshin): a very impressive progress! established observations of charge-dependent hadron correlations from STAR and ALICE; ATLAS results coming soon The theory community should do everything possible to help the experiments to reliably extract the deep physics contained in the data 25

26 Theory : Current status the ideas on the interplay of magnetic field and chirality validated, the existence of CME is established Next stage: using CME, CVE, CMW to extract the information about topological contents of QGP To succeed, we need reliable theoretical tools (Chiral Magneto-Hydro-Dynamics, CMHD, Chiral Kinetic Theory, ) and fully quantitative studies 26

27 Chiral Magneto-Hydrodynamics (CMHD) Consistent theory of relativistic fluids with chiral fermions XXI century development in hydrodynamics! Describes qualitatively new phenomena: Chiral Magnetic Effect (CME), Chiral Vortical Effect (CVE), Chiral Magnetic Wave (CMW), Talk by D. Son 27

28 Chiral Magnetic Effect from anomalous 3D hydrodynamics Chiral charge density Electric charge density Talk by Yuji Hirono Y. Hirono, T. Hirano and D. Kharzeev, arxiv:

29 The development of CMHD (quantum anomalies, dynamical electromagnetic fields, finite baryon density, direct comparison to experimental observables) is one good example (out of many) of why we need a concerted collaborative effort of theorists and experimentalists a topical collaboration in Nuclear Theory? Discussion led by J. Liao and H.Huang 29

30 Topical collaboration It would be natural to focus on the physics of BES-II experimental program at RHIC (vorticity, baryon density, ) Synergy with the study of QCD phase diagram and the Critical Point closely related physics, need the same theoretical tools (CMHD, ) Multi-institutional, international initiative linking theory and experiment 30

31 Anomalous transport of charge a gateway to the geometry of gauge fields that defines the properties of QCD The study of this physics in heavy ion collisions will have broad implications across many fields (condensed matter, astrophysics, cosmology, ) Let us do it together! 31