Russian Academy of Sciences

Landau Institute for Theoretical Physics


Regular seminars are held on Thursdays in the Kapitza Institute in Moscow and on Fridays at the scientific council of the Landau Institute in Chernogolovka.

Departments of the institute hold their own seminars; the topic are determined by the scientific orientation of the related department.

Seminars information is also sent via e-mail. If you want to receive seminar announcements, please subscribe.

Recent applications of the light-cone path integral formalism to the radiative effects in $AA$-collisions due to the induced gluon/photon emission in the QCD matter

18 January, the day after tomorrow in 11:30 at scientific council

B.G. Zakharov

In this talk I discuss some recent applications of the light-cone path integral (LCPI) approach to the induced gluon/photon emission in the quark-gluon plasma (QGP) in $AA$-collisions at RHIC-LHC energies. I start with a brief discussion of the basic formulas of the LCPI formalism. Then I present the results for the nuclear modification of the photon-tagged jets in $AA$ collisions within the jet quenching scheme based on the LCPI approach to the induced gluon emission. The calculations are performed for running coupling. Collisional energy loss is treated as a perturbation to the radiative mechanism. We obtain a reasonable agreement with the recent data from the STAR Collaboration on the mid-rapidity nuclear modification factor $I_{AA}$ for Au+Au collisions at $\sqrt{s}=200$ GeV for parametrization of running $\alpha_s$ consistent with that necessary for description of the data on suppression of the high-$p_T$ spectra. The main part of the talk will be devoted to the radiative contribution to the jet $p_T$-broadening in the QGP. For the first time the analysis of the radiative $p_T$-broadening of a fast quark in the QGP is performed accounting for the real and virtual two-parton states beyond the soft gluon approximation. It is shown that radiative processes can strongly suppress the radiative $p_T$-broadening in the QCD matter (and even make it negative). This prediction is qualitatively different from the results of previous analyses in th soft gluon approximation in the double logarithmic approximation (B. Wu, JHEP 1110, 029 (2011); T. Liou, A. H. Mueller and B. Wu, Nucl. Phys. A916, 102 (2013); J.-P. Blaizot and Y. Mehtar-Tani, Nucl. Phys. A929, 202 (2014)) predicting that radiative processes should significantly increase $p_T$-broadening. Our prediction is consistent with the recent data of the STAR Collaboration (L. Adamczyk et al., Phys.Rev. C96, 024905 (2017)), which do not show any signal of $p_T$-broadening in Au+Au collisions at the energy 200 GeV. At the end of the talk I discuss the the role of running coupling and the effect of variation of the thermal quark mass on contribution of the collinear bremsstrahlung and annihilation to photon emission in $AA$ collisions in a scheme similar to that used in our previous jet quenching analyses.

Inelastic neutron scattering as a confirmation of a new type of gapped surface excitations in liquid helium

18 January, the day after tomorrow in 11:30 at scientific council (short)

P.D. Grigoriev, A.D. Grigoriev, A.M. Dyugaev

We analyze the experimental data on inelastic neutron scattering by a thin ~5-atomic-layer film of liquid helium at three different temperatures: T=0.4K, 0.98K and 1.3K. The neutron scattering intensity plots, in addition to the previously know dispersion of phonons and ripplons, suggest a branch of gapped surface excitations with activation energy ~4.5K and the dispersion similar to that expected for surfons -- the bound quantum states of helium atoms above liquid helium surface, proposed and investigated theoretically. These data, probably, provide the first direct experimental confirmation of surfons. Before these surface excitations received only indirect experimental substantiation, based on the temperature dependence of surface tension coefficient and on their interaction with surface electrons. The existence of surfons as an additional type of surface excitations, although being debated yet, is very important for various physical properties of He surface. We also analyze previous numerical results on excitations in liquid helium and argue that surface excitations similar to surfons have been previously obtained by numerical calculations and called resonance interface states.

Linear magnetoresistance in the charge density wave state of quasi-two-dimensional rare-earth tritellurides

18 January, the day after tomorrow in 11:30 at scientific council (short)

P.D. Grigoriev

The magnetoresistance of a TbTe3 two-dimensional conductor with a charge-density wave (CDW) has been measured in a wide temperature range and in magnetic fields of up to 17 T. At temperatures well below the Peierls transition temperature and in high magnetic fields, the magnetoresistance exhibits a linear dependence on the magnetic field caused by the scattering of normal charge carriers by “hot” spots of the Fermi surface. In the sliding CDW regime in low magnetic fields, a qualitative change in the magnetoresistance has been observed associated with the strong scattering of carriers by the sliding CDW.
[1] A.V. Frolov, A.P. Orlov, P.D. Grigoriev, V.N. Zverev, A.A. Sinchenko, P. Monceau, Magnetoresistance of a Two-Dimensional TbTe3 Conductor in the Sliding Charge-Density Wave Regime, JETP Lett., 107(8), 488-492 (2018)

Pretsessiya spina zaryazhennoi chastitsy s MDM i EDM v gravitatsionnom pole Zemli

25 January in 11:30 at scientific council (short)

S.N. Vergeles, N.N. Nikolaev

Vychislena uglovaya skorost’ pretsessii spina zaryazhennoi chastitsy s MDM i EDM v gravitatsionnom pole Zemli s uchyotom sutochnogo vrashcheniya. Khotya bol’shaya chast’ rezul’tata yavlyaetsya klassicheskoi i khorosho izvestnoi, vklad v pretsessiyu ot sutochnogo vrashcheniya do sikh por yavlyaetsya diskussionnym. Korrektnyi uchyot etogo vklada predstavlyaetsya neobkhodimym, tak kak eto vliyaet na pravil’nuyu traktovku eksperimentov po pretsessii spina v uskoritelyakh.

Generirovanie effektivnoi fermionnoi vershiny gravitatsionnym instantonom v reshetochnoi teorii gravitatsii

25 January in 11:30 at scientific council (short)

S.N. Vergeles

Pokazano, chto v reshetochnoi gravitatsii, svyazannoi s fermionami, voznikayut effektivnye fermionnye vershiny. Eti vershiny generiruyutsya gravitatsionnymi instantonami, analogichno tomu kak voznikayut effektivnye fermionnye vershiny v teorii Yanga-Millsa vsledstvie nalichiya fermionnykh nulevykh mod, svyazannykh s instantonami.

Collinear photon emission from the quark-gluon plasma in heavy ion collisions

25 January in 11:30 at scientific council

B.G. Zakharov

Making use the light-cone path integral scheme we develop a formalism for collinear photon emission from the quark-gluon plasma (QGP) that accounts for accurately the Landau-Pomeranchuk-Migdal effect. In the case of the QGP without magnetic field we reproduce the AMY (Arnold, Moore, Yaffe (2001)) photon spectrum obtained within the thermal field theory. In the first part of the talk we study the role of running coupling and the effect of variation of the thermal quark mass on contribution of the collinear bremsstrahlung and quark-antiquark annihilation to photon emission in AA collisions in a scheme similar to that used in our previous jet quenching analyses. We find that for a scenario with the thermal quark mass about 50-100 MeV contribution of the higher order collinear processes summed with the 2 \to 2 processes can explain a considerable part (about 50%) of the experimental photon spectrum at k_T about 2-3 GeV for Au+Au collisions at $\sqrt{s}=0.2$ TeV. But for quark mass 300 MeV and for the thermal quark mass predicted by the hard thermal loop scheme the theoretical predictions underestimate considerably the experimental spectrum. In the second part of the talk we discuss a generalization of our formalism to the QGP with magnetic field. We then use it to investigate the effect of magnetic field on the photon emission from the QGP created in AA collisions. We find that even for very optimistic assumption on the magnitude of the magnetic field generated in AA collisions its effect on the photon emission rate is practically negligible. For this reason the magnetic field cannot generate a significant azimuthal asymmetry in the photon spectrum as it was suggested in the analysis by Tuchin (K. Tuchin, Phys. Rev. C{\bf 91}, 014902 (2015)).

JKLMR conjecture and Batyrev construction

1 February in 11:30 at scientific council

A. Belavin, A. Aleshkin, A. Litvinov

JKLMR gipoteza predpolagaet svyaz’ mezhdu tochnoi vychislennoi statsummoi nekotoroi Kalibrovochnoi supersimmetrichnoi Sigma-model’yu Vittena i Geometriei na prostranstve polei effektivnoi teorii polya, voznikayushchei v teorii Superstrun, kompaktifitsirovannoi na mnogoobrazie Kalabi-Yao. Ya rasskazhu o tom, kak ispol’zuya dual’nost’ mezhdu mnogrannikami Batyreva, ustanovit’ vysheukazannoe sootvetstvie tochno.
arXiv:1812.00478, submitted to Journal Statistical Physics

Ergodicheskie svoistva dinamicheskikh sistem na dvumernykh poverkhnostyakh i elektronnye transportnye yavleniya v normal’nykh metallakh

1 February in 11:30 at scientific council (short)

A.Ya. Mal’tsev, S.P. Novikov

V doklade obsuzhdaetsya svyaz’ spetsial’nykh kharakteristik dinamicheskikh sistem na poverkhnostyakh (indeksov Zoricha - Kontsevicha - Forni) s povedeniem provodimosti v metallakh v sil’nykh magnitnykh polyakh. Dannoe rassmotrenie yavlyaetsya vazhnym v sluchae vozniknoveniya naibolee slozhnykh (khaoticheskikh) elektronnykh traektorii na poverkhnosti Fermi, vozmozhnom dlya dostatochno slozhnykh poverkhnostei i spetsial’nykh napravlenii magnitnogo polya. Kak mozhno pokazat’, upomyanutye kharakteristiki imeyut neposredstvennoe otnoshenie k povedeniyu magnitoprovodimosti, takim obrazom, mozhno v printsipe govorit’ o vozmozhnosti ikh eksperimental’nogo opredeleniya v sootvetstvuyushchikh sluchayakh.

On complex angular diagrams of magnetic conductivity in strong magnetic fields

1 February in 11:30 at scientific council (short)

A.Ya. Maltsev

We consider angular conductivity diagrams for normal (single-crystal) metals with complex Fermi surfaces in the presence of strong magnetic fields. The behavior of conductivity in this case strongly depends on the direction of the magnetic field and the stable nontrivial regimes of this behavior correspond to special zones of stability on the angular diagram corresponding to certain (topological) properties of the conductivity tensor. As we show, in the general case such diagrams can be divided into two general types, simple (type A) and complex (type B). We will be interested in the diagrams of the second type, which have a number of specific features (an infinite number of stability zones, the presence of chaotic regimes, etc.), which we will consider in more detail.

Three-dimensional numerical simulation of long-lived quantum vortex knots and links in a trapped Bose-Einstein condensate

8 February in 11:30 at scientific council (short)

V.P. Ruban

Dynamics of simplest vortex knots, unknots, and links of torus type inside an atomic Bose-Einstein condensate in anisotropic harmonic trap at zero temperature has been numerically simulated using three-dimensional Gross-Pitaevskii equation. The lifetime for such quasi-stationary rotating vortex structures has been found quite long in wide parametric domains of the system. This result is in qualitative agreement with a previous prediction based on a simplified one-dimensional model approximately describing dynamics of vortex filaments.


8 February in 11:30 at scientific council

V.G. Marikhin, A.V. Marikhina

One of us previously obtained and integrated the first examples of two-dimensional Schr¨odinger equations with a magnetic field belonging to the class of quasi–exactly solvable problems. It was shown that the wave functions are expressed in terms of degenerations of the Heun function: biconfluent and confluent Heun functions. Algebraic conditions were also found that determine the discrete spectrum and wave functions. Our goal here is to solve these algebraic equations numerically. In some cases, we can find an analytic approximation of the discrete spectrum.

Hermite quasi-polynomials

8 February in 11:30 at scientific council (short)

V.G. Marikhin

The Hermite quasi-polynomials are obtained (the square root of the weight coincides with the Hermite one). The corresponding spectral problem with singularity at zero is constructed. The space to which belong the eigenfunctions of the above-mentioned spectral problem is constructed. The kind of this space solves the paradox with singularity.

Perkolyatsiya i dzhamming obraztsov sluchainoi posledovatel’noi adsorbtsii dlinnykh k-merov na kvadratnoi reshetke

8 February in 11:30 at scientific council (short)

L.Yu. Barash

Pri pomoshchi komp’yuternogo modelirovaniya izuchayutsya perkolyatsionnyi perekhod i sostoyanie dzhamminga v modeli izotropnoi sluchainoi posledovatel’noi adsorbtsii. Razrabotan parallel’nyi algoritm, kotoryi ochen’ effektiven s tochki zreniya ego skorosti i ispol’zovaniya pamyati, i primenen k modeli sluchainoi posledovatel’noi adsorbtsii dlinnykh k-merov na kvadratnoi reshetke s periodicheskimi granichnymi usloviyami. Vychisleny porogovye plotnosti perkolyatsii i dzhamminga dlya dlin k-merov vplot’ do 131072. Ranee v literature takie vychisleniya provodilis’ tol’ko dlya k ≤ 512. Naiden rezhim povedeniya perkolyatsionnoi plotnosti dlya bol’shikh dlin chastits. Proanalizirovana struktura perkolyatsionnogo i dzhammingovogo sostoyanii. Teoreticheskie rezul’taty raboty [G. Kondrat et al., Phys. Rev. E 022154, 2017] obobshcheny na sluchai periodicheskikh granichnykh uslovii. Dokazano, chto lyuboi klaster v sostoyanii dzhamminga yavlyaetsya perkolyatsionnym klasterom, i chto perkolyatsiya voznikaet do dzhamminga.
Soobshchenie po rezul’tatam raboty M.G. Slutskii, L.Yu. Barash, Yu.Yu. Tarasevich, Percolation and jamming of random sequential adsorption samples of large linear k-mers on a square lattice, Phys. Rev. E 98, 062130 (2018).

Laser technologies: science and applications

15 February in 11:30 at scientific council

N.A. Inogamov

In the first part of report the combined action of laser and plasmonic electromagnetic fields which dissipate in a metal film is considered. Fast dissipation of energy of light causes mechanical response moving a film. Motion and subsequent fast re-crystallization result in formation of surface micro-structures used for holographic purposes [1,2]. In the second part the physics of laser fragmentation of a liquid tin micro-droplet is analyzed. This is important for development of next generation of photo-lithography machines [3]. In the third part the indirect monitoring shot-to-shot shock waves strength reproducibility during the pump-probe experiments is studied [4]. The calibrated laser source is used after this checking for generation of shocks; goals for employing of these shocks are described in Albertazzi et al., Science Advances, 3(6), e1602705 (2017). [1] J. Phys.: Conf. Ser., 1092, 012051 (2018) [2] J. Phys.: Conf. Ser., 1092, 012052 (2018) [3] Phys. Rev. Applied 10, 064009 (2018) [4] J. Appl. Phys. 120, 035901 (2016)

Shock generation by laser and impact initiation of burning

15 February in 11:30 at scientific council

N.A. Inogamov

Generation of shocks by an ultrashort laser pulse is considered. Elastic-plastic response and polymorphic alpha-epsilon transition in iron are analyzed [1,2]. Initiation of initial stages of burning of high explosives by slow impact is studied [3]. Burning is caused by dissipative heating during plastic deformations. [1] S.I. Ashitkov, V.V. Zhakhovsky, N.A. Inogamov, P.S. Komarov, M.B.Agranat, and G.I.Kanel, The behavior of iron under ultrafast shock loading driven by a femtosecond laser, AIP Conf. Proc. 1793, 100035 (2017) [2] V.V. Zhakhovsky, K.P. Migdal, N.A. Inogamov, S.I. Anisimov, MD simulation of steady shock-wave fronts with phase transition in single-crystal iron, AIP Conf. Proc. 1793, 070003 (2017) [3] D. Ilnitsky, N. Inogamov, V. Zhakhovsky, Response of explosive HMX to low-velocity impact: Modeling by the crystal plasticity finite element method, J. Phys.: Conf. Ser., 941, 012052 (2018)

22 February in 11:30 at scientific council

Ferdinand Evers (Regensburg University)


Non-ergodic phase of the Quantum Random Energy Model

1 March in 11:30 at scientific council

L. Faoro, M. Feigel'man, L. Ioffe

Pokazano, chto fazovaya diagramma odnoi iz prosteishikh modelei kvantovogo spinovogo stekla – kvantovogo obobshcheniya modeli Derridy sluchainykh urovnei energii – obladaet neergodicheskoi delokalizovannoi fazoi s vremenem relaksatsii, eksponentsial’no dlinnym po chislu spinov n. Kak vremya relaksatsii, tak i ob’em Gil’bertova prostranstva, zanimaemyi mnogochastichnoi volnovoi funktsiei, yavlyayutsya stepennymi funktsiyami polnoi razmernosti Gil’bertova prostranstva N = 2^n. Oba eti pokazateli stepeni naideny v ramkakh priblizhennoi analiticheskoi teorii, poluchennye dlya nikh otvety neplokho soglasuyutsya s rezul’tatami pryamoi chislennoi diagonalizatsii. Poluchennye rezul’taty mogut byt’ polezny dlya fizicheskoi realizatsii kvantovogo simulyatora dlya resheniya zadach algoritmicheskoi optimizatsii tipa number partitioning.

Izuchenie sosushchestvovaniya faz v plenkakh smektikov v okrestnosti TKT dlya perekhoda geksatik - smektik A.

1 March in 11:30 at scientific council

V.V. Lebedev, E.S. Pikina , E.I. Kats

V rezul’tate teoreticheskogo analiza eksperimental’nykh dannykh po rasseyaniyu rentgenovkikh luchei na tonkikh svobodno podveshennykh plenkakh (SPP) zhidkogo kristalla 54COOBC vblizi fazovogo perekhoda smektik-A – geksatik ustanovleno, chto perekhod proiskhodit pervym rodom i vyyavlen temperaturnyi interval sosushchestvovaniya ukazannykh faz, kotoryi umen’shaetsya s umen’sheniem tolshchiny plenki. Eksperimental’nye dannye ob’yasnyayutsya blizost’yu sistemy k trikriticheskoi tochke (TKT). V ramkakh fenomenologicheskoi teorii fazovykh perekhodov Landau s vklyucheniem v rassmotrenie poverkhnostnykh effektov opredelena zavisimost’ shiriny dvukhfaznoi oblasti ot tolshchiny SPP v okrestnosti TKT. Analiticheskie raschety khorosho soglasuyutsya s rezul’tatami eksperimenta, i podtverzhdayut anomal’no glubokoe proniknovenie geksaticheskogo uporyadocheniya v SPP vblizi TKT. Zavisimost’ temperaturnogo intervala sosushchestvovaniya faz ot tolshchiny plenki svyazana s bol’shoi dlinoi korrelyatsii geksaticheskogo parametra poryadka. Poluchennye rezul’taty demonstriruyut unikal’nuyu vozmozhnost’ priblizheniya k trikriticheskoi tochke na linii fazovykh perekhodov smektik A - geksatik za schet izmeneniya tolshchiny plenki. Predlozhennyi podkhod mozhet byt’ primenen k shirokomu klassu sistem, obladayushchikh TKT.
Doklad osnovan na rabote: Evidence of a first-order smectic – hexatic transition and its proximity to tricritical point in smectic films., I.A. Zaluzhnyy, R.P. Kurta, N. Mukharamova, Y.Y. Kim, R.M. Khubbutdinov, D. Dzhigaev, V.V. Lebedev, E.S. Pikina, E.I. Kats, N.A. Clark, M. Sprung, B.I. Ostrovskii, I.A. Vartanyants, Phys. Rev. E, v. 98, p. 052703 (2018)

SYK model with quadratic perturbations: the route to a non-Fermi-liquid

15 March in 11:30 at scientific council

A.V. Lunkin, K.S. Tikhonov, M.V. Feigel’man

V rabote rassmatrivaetsya SYK (Sachdev-Ye-Kitaev) model’ s kvadratichnym vozmushcheniem v predele bol’shogo no konechnogo chisla fermionov. Rassmatrivaya teoriyu vozmushcheniya po amplitude vzaimodeistviya my pokazali, chto povedenie funktsii Grina G(τ)~τ^(-3/2) v infrakrasnom predele ne izmenyaetsya, pri dostatochno malom vozmushchenii. Takzhe etot rezhim byl issledovan chislenno s pomoshch’yu tochnoi diagonalizatsii Gamil’toniana.

11 April in 11:30 in Kapitza Institute

Yan Fyodorov