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Observing a Global Delocalization Transition in the de MouraLyra Model
(CFP room (326), from
20190531 14:30 to
20190531 15:30)

The possibility of having a delocalisation transition in the 1D de MouraLyra class of models (having a powerspectrum $q^{\alpha}$) has been the object of a long standing discussion in the literature.
In this seminar, we report the first numerical evidences that such a transition happens at $\alpha=1$, where the localisation length (measured from the scaling of the conductance) is shown to diverge as $(1\alpha)^{1}$. The persistent finitesize scaling of the data is shown to be caused by a very slow convergence of the nearestneighbor correlator to its infinitesize limit, and controlled by the choice of a proper scaling parameter. Our results for these models are consistent with a localisation of eigenstates that is driven by a persistent smallscale noise, which vanishes as $\alpha\to1^{}$. This interpretation in confirmed by analytical perturbative calculations which are built on previous work.
Finally, the nature of the delocalisation transition is discussed and the conclusions are illustrated by numerical work done in the $\alpha>1$ regime.

Colliders and conformal interfaces
(CFP room (326), from
20190517 14:00 to
20190517 15:00)

We set up a scattering experiment of matter against an impurity which separates two generic onedimensional critical quantum systems. We compute the flux of reflected and transmitted energy, thus defining a precise measure of the transparency of the interface between the related twodimensional conformal field theories. If the largest symmetry algebra is Virasoro, we find that the reflection and transmission coefficients are independent of the details of the initial state, and are fixed in terms of the central charges and of the twopoint function of the displacement operator. The situation is more elaborate when extended symmetries are present. Positivity of the total energy flux at infinity imposes bounds on the coefficient of the twopoint function of the displacement operator, which controls the freeenergy cost of a small deformation of the interface.

Holographic modeling of neutron stars
(CFP room (326), from
20190515 14:00 to
20190515 15:00)

Gauge/gravity duality can be used to study QCD at high densities and low temperatures where many other theoretical tools do not work. In particular one may constrain the equation of state of QCD matter in neutron star cores, which currently has large theoretical uncertainties. I will review recent progress on this topic. Bottomup models which are carefully fitted to available data suggest that the equation of state is stiff (i.e., the speed of sound is high) in the nuclear matter phase and soft (i.e, the speed of sound is low) in the quark matter phase. The two phases are separated by a strong first order phase transition, which makes quark matter cores of neutron stars unstable. This picture agrees with current experimental constraints from LIGO/Virgo and from Shapiro delay measurements. This Journal Club was supported by the project UID/FIS/04650.

Positive helicity EinsteinYangMills Amplitudes from the Double Copy
(CFP room (326), from
20190514 14:00 to
20190514 15:00)

All positive helicity fourpoint gluongraviton amplitudes in EinsteinYangMills theory coupled to a dilaton and axion field are computed at the leading oneloop order using the double copy method. Using the double copy method the gravity integrand is obtained from integrands of a gauge theory. The resulting purely rational expressions take very compact forms. The previously seen vanishing of the singlegravitonthreegluon amplitude at leading order in $\kappa$ is seen to be lifted at order $\kappa^{3}$.

An introduction to (improved) holographic QCD
(CFP room (326), from
20190513 14:00 to
20190513 15:00)

I start with a generic review of gauge/gravity duality and discuss how it can be used to obtain information for QCD in the strongly coupled regime. I give a brief discussion of various topdown and bottomup approaches. I go on presenting in detail a specific class of models, that is improved holographic QCD (IHQCD) and VQCD. IHQCD and VQCD are bottomup models for YangMills theory in the 't Hooft limit and for QCD in the Veneziano limit, respectively. I demonstrate that these models compare well with available data for QCD.
This Journal Club is supported by the project UID/FIS/04650.

Scattering States in AdS/CFT
(CFP Room (326 DFA), from
20190322 13:30 to
20190322 14:30)

We show that suitably regulated multitrace primary states in large N CFTs behave like `in' and `out' scattering states in the flatspace limit of AdS. Their transition matrix elements approach the exact scattering amplitudes for the bulk theory, providing a natural CFT definition of the flat space SMatrix. We study corrections resulting from the AdS curvature and particle propagation far from the center of AdS, and show that AdS simply provides an IR regulator that disappears in the flat space limit.

Entanglement and formation of Black Holes
(CFP room (326), from
20190227 14:00 to
20190227 15:00)


"Holography, higher spin and gravity"
(CFP Room (326), from
20190225 13:30 to
20190225 14:30)


A tale of three models  How annealing can give rise to localization, liquids phases, and topological order.
(CFP Room (326), from
20190130 14:00 to
20190130 15:00)

Annealed, as opposed to quenched, degrees of freedom are allowed to choose their equilibrium state rather than remaining frozen in a predetermined configuration. Models of annealed classical degrees of freedom in contact with quantum mechanical variables can emerge in the presence of quasiconserved quantities or as effective descriptions of collective excitations, valid away from the zero temperature limit. In contrast to their classical counterparts, these models can be efficiently simulated by classical Monte Carlo algorithms. The FalicovKibble (FK) model is the simplest of this kind. It has been widely studied and used as testing grounds to dynamical mean field theory methods.
In this talk, I will first show that the phase diagram of the FK model still held some surprises, including an example of a disorderedfree localized phase. Second, I will show that introducing frustration, by going to the triangular lattice, an FKlike model can support rather exotic liquid phases. Thirdly, I will show how FK interactions affect the topological properties of the Haldane model.
References:
[1] Interactiontuned Anderson versus Mott localization
A. E. Antipov, Y. Javanmard, P. Ribeiro, S. Kirchner
Phys. Rev. Lett. 117, 146601 (2016)
[2] Classical and quantum liquids induced by quantum fluctuations.
M. M. Oliveira, P. Ribeiro, S. Kirchner.
arXiv:1810.10582 (2018)
[3] Temperaturedriven gapless topological insulator.
M. Gonçalves, P. Ribeiro, R. Mondaini, E. V. Castro.
arXiv:1808.00978 (2018)

Manybody localization and Thermalization in isolated quantum systems
(, from
20190114 22:32 to
20190114 22:32)

The fundamental question of how an isolated interacting quantum
system, subjected to only unitary timeevolution, loses information about
its initial preparations has been the focus of a variety of studies [1, 2]. More recently, however,
another angle of this problem has also been investigated: When they are
influenced by quenched disorder, information of the initial conditions can
be preserved for arbitrarily long times, whose potential application to
quantum memories is immediate. This phenomenon is dubbed manybody
localization and can be seen as the generalization of the fundamental
problem of the Anderson localization when its constituents are interacting.
In this talk, I will present an overall picture of this interplay of the
manybody localization [3, 4] and thermalization [5, 6], describing the
conditions they are manifest.
Importantly, it has been the focus of not only numerical studies but also of
experimental ones, via the emulation in optical lattices trapping cold atoms
[7, 8]. I will also glance on some recent generalizations investigated by
our group showing that manybody localization may also be manifest
in systems that are translationally invariant, i.e., even in the absence of
quenched disorder [9], and the possible investigation of manybody mobility edges. [10]
[1] M. Srednicki, Phys. Rev. E 50, 888 (1994)
[2] M. Rigol, V. Dunjko, and M. Olshanii, Nature 452, 854858 (2008)
[3] R. Mondaini, M. Rigol, Phys. Rev. A 92, 041601(R) (2015)
[4] C. Cheng, R Mondaini, Phys. Rev. A 94 (5), 053610 (2016)
[5] R. Mondaini, K. R. Fratus, M. Srednicki, M. Rigol, Phys. Rev. E 93 (3),
032104 (2016)
[6] R. Mondaini and M. Rigol, Phys. Rev. E 96, 012157 (2017)
[7] M. Schreiber, S. S. Hodgman, P. Bordia, H. P. Luschen, M. H. Fischer, R.
Vosk, E. Altman, U. Schneider, I. Bloch, Science 349, 842 (2015)
[8] J.Y. Choi, S. Hild, J. Zeiher, P. Schauß, A. RubioAbadal, T. Yefsah,
V.Khemani, D. A. Huse, I. Bloch, and C. Gross, Science 352, 1547 (2015)
[9] R. Mondaini and Z. Cai, Phys. Rev. B 96, 035153 (2017)
[10] Xing Bo Wei, Chen Cheng, Gao Xianlong, Rubem Mondaini, arXiv:1810.08209