Math Phys seminar

**Speaker: Jorge Laraña Aragon,University of Stockholm**

**Title: Quenched coupling, effective thermalization and evanescence in the free $O(N)$ vector model**

Room: VR-II, V-156

Time: Thursday 15th August, 14:00hrs

#### Abstract:

In this project we study two coupled free $O(N)$ vector models implementing the coupling via a quench of mixing. Since the theory is integrable pure thermalization does not occur but the quantum modes thermalize independently. Generalized thermal behavior is obtained at late times in the limit of weak initial mixing. We investigate this from both the effective density matrix and the spectral density function. When computing the latter, we observe that late-time correlation functions of composite operators in the post-quench free QFT surprisingly share interesting properties with correlators in strongly coupled systems. We discuss a possible holographic interpretation in terms of the so called evanescent modes.

Math Phys seminar

### Speaker: Christiana Pantelidou, Durham University

### Title: Incoherent hydrodynamics and density waves

Location: VR-II, V-258

Time: Monday June 24 at 2.00 pm

### Abstract:

I will consider thermal phases of holographic lattices at finite chemical potential in which a continuous internal bulk symmetry can be spontaneously broken. In the normal phase, translational symmetry is explicitly broken by the lattice and the long wavelength excitations are captured by incoherent hydrodynamics describing two perturbative diffusive modes. In the broken phase an additional diffusive hydrodynamic degree of freedom appears. In this talk I will use holography to write an effective theory describing the coupling of incoherent hydrodynamics to this goldstone mode.

Math Phys Seminar

### Speaker: Bo Sundborg, Stockholm University

### Title: Field theory compositeness, holographic gravity and higher spins

Location: Tg 227 (“smart room” Tæknigarður)

Time: Tuesday April 30 at 14.00 am

### Abstract:

I would like to discuss the idea that composite operators in field theory

are key ingredients in holograms of bulk gravitational physics. In practice,

this is well known: Composites are essential in both matrix (Maldacena) and vector (Klebanov-Polyakov) AdS/CFT. I argue that composite correlators in thermal and quenched field theory backgrounds illuminate the importance of compositeness further. They behave as boundary-boundary correlators in geometries with a strong gravitational source in the interior, whether the bulk is Einsteinian or higher spin-like.

Math Phys Seminar

### Speaker: Lukas Schneiderbauer, HÍ

### Title: Holographic Complexity of Two-Dimensional Black Holes

Location: VR-II 158

Time: Monday April 29 at 10.00 am

### Abstract:

Interest in holographic complexity arose when it was proposed as the dual quantity of the complexity of a quantum state in the context of AdS/CFT. However, it was realized that this quantity behaves reasonably even for geometries which are asymptotically flat and therefore do not fall under the AdS/CFT umbrella.

Motivated by this, we adapt and evaluate proposals for holographic complexity in black hole solutions of the CGHS model and variants thereof. These solutions describe 1+1 dimensional black hole geometries which are asymptotically flat.

The advantage of working with these models is that they allow for analytic treatment even in time-dependent backgrounds such as gravitational collapse or even black hole evaporation.

Math Phys/Phys seminar

### Speaker: Jens H. Bárðarson, KTH Stockholm

### Title: On the chiral anomaly in Weyl semimetals

Location: VR-II 158

Time: Tuesday December 4, at 13.30

### Abstract:

I will give an introduction to the physics of Weyl semimetals focussing on Fermi arcs and chiral anomaly. I will then discuss some transport properties of Weyl semimetals including strongly angular-dependent magnetotransport in the presence of long range disorder, and the difference between the longitudinal conductance in the presence of magnetic field and chiral pseudo-magnetic field. The latter points in opposite direction for opposite chiralities and can be induced, for example, by strain. This leads to a discussion of pseudo-landau levels and their connection with Fermi arcs and covariant and consistent chiral anomaly. I will also mention a new axial torsional contribution to the axial anomaly.

Math Phys seminar

### Speaker: Aruna Rajagopal, University of Iceland

### Title: Shock and Rarefaction Waves in Out of Equilibrium Lifshitz Fluids

Location: VR-II 155

Time: Thursday November 22 at 13.30

### Abstract:

Motivated by the recent developments and interest in the emergence of a non equilibrium steady state or NESS, for a relativistic fluid, and its possible holographic dual, we follow a similar framework to study the properties of such a state for a non-relativistic Lifshitz fluid with a general scaling exponent. This is carried out by solving the Riemann problem for the NESS which develops between two semi-infinite heat reservoirs that are brought into contact, and studying the shock and rarefaction waves which emerge as solutions to this problem.

Math Phys seminar

### Speaker: Daniel Areán, IFT Madrid

### Title: Breaking translations in AdS/CMT: Holographic Bad Metals

Location: Naustið (Endurmenntun)

Time: Wednesday October 24, 13.30 – 14.30

### Abstract:

We present holographic models realizing the pseudo-spontaneous breaking of translations. We study the electrical transport of these solutions finding that they reproduce features characteristic of the bad metallic transport observed in the cuprates.

Math Phys seminar

### Speaker: Tobias Zingg, Nordita

### Title: plasmons and physical density-density response from holography

Place: Aðalbygging A-069

Time: Thursday October 4, at 1.20 – 2.20 pm

### Abstract:

The holographic correspondence can be extended to identify plasmonic excitations in strongly correlated systems. These modes have relevance in the growing field of plasmonics, and play also a crucial role in relating properties of holographic ‘screened’ density-density response response functions to ‘physical’ density-density response functions, with the latter being the quantity actually related to experimental observation.

Math Phys seminar

### Speaker: Kevin John Torres Grosvenor, Niels Bohr Institute

### Title: Nonrelativistic Naturalness and the quest for Emergent Lorentz Symmetry

Location: V-147 (VR-II)

Time: Tuesday 22 May at 10:30

### Abstract:

I will discuss our proposal for a nonrelativistic solution to the Higgs mass hierarchy problem, its dependence on the emergence of various shift symmetries, and the role it might play in the search for a nonrelativistic theory of particle physics in which Lorentz symmetry emerges at “low” energies.

Math Phys seminar

### Speaker: Matteo Baggioli, Autonomous University of Barcelona

### Title: Holographic quantum phase transitions: time to get dirty!

Location: HB-5 (Háskólabíó)

Time: Monday 9 April at 10:50

### Abstract:

We study the effects of quenched one-dimensional disorder on the holographic Weyl semimetal quantum phase transition (QPT). We observe the smearing of the sharp QPT linked to the appearance of rare regions at the horizon where the local order parameter is non-zero. We discuss the role of the disorder correlation and we compare our results to the weakly coupled expectations from condensed matter theory and simulations. We analyze also the interplay of finite temperature and disorder and we find preliminary indications for the presence of log-oscillatory structures in the order parameter.