Holography for Astrophysics and Cosmology

19 Oct 2022, 09:00 → 21 Oct 2022, 18:00 Europe/Stockholm

Conference center, room ... (Albano Building 3)

Javier Subils (Stockholm University), Ronnie Rodgers (Stockholm University)

Scope

We gather world experts working on applications of gauge/gravity duality to astrophysical and cosmological phenomena. 

We will hear how holography is applied in the context of neutron stars, where the density is too large for the use of lattice simulations, but not large enough for perturbation theory to be applicable. We will learn about the production of gravitational waves in the early universe, when a first-order phase transition of a strongly coupled extension of the Standard Model would lead to imprints in the gravitational wave signal.

This program will consist of several one and a half hour talks by the invited speakers, plus a small number of additional selected contributions from other participants. This format is aimed to foster discussions and fruitful collaborations. 

Download the poster of the conference here [ pdf ]

Invited speakers

• Francesco Bigazzi 
• Nick Evans
• Carlos Hoyos
• Thomas Konstandin
• David Mateos
• Kostas Skenderis
• Aleksi Vuorinen
• Ivonne Zavala

Application/Registration

There is no registration fee. Application is opened now until September 18 in this webpage.

Accommodation information and travel support

Accommodation costs may be covered for a limited number of PhD students and/or junior researchers. Applicants are encouraged to indicate in the registration form whether they need travel support.

Social events

There will be a conference dinner on Thursday 20.
The method of payment (700 SEK) will be specified after the registration deadline.

Organisers

Antón Faedo, Oscar Henrikson, Matti Järvinen, Ronnie Rodgers and Javier Subils

Sponsored by:

Logo Sponsors.png

PosterWorkshop_v2.pdf

Slides

• hoyos_EffectActGWs.pdf
• skenderis_Nordita2022.pdf
• Talk_Zavala.pdf

Wednesday, 19 October

1 Gravitational waves from cosmological phase transitions

I will discuss the state-of-the-art of predicting and experimentally testing a stochastic background of gravitational waves produced by cosmological first-order phase transitions. I focus on recent developments in understanding the dynamics of the primordial fluid after percolation and how to connect simulation results to observations and model building.

Speaker: Thomas Konstandin

konstandin.mp4

Konstandin.pdf

10:30 Coffee break

2 AdS/CAP

The discovery of gravitational waves has opened a new experimental window into the Universe. The fact that the relevant physics is often out of equilibrium offers a golden opportunity for holography to make a unique impact on cosmology and astrophysics. I will review recent progress in this direction, with a focus on cosmological phase transitions and neutron star mergers. I will also discuss a new holographic framework to describe strongly coupled matter coupled to dynamical gravity. If time permits I will mention applications to baryogenesis, thermal inflation and primordial black holes. No prior knowledge of string theory or holography required.

Speaker: David Mateos

Mateos Nordita Oct 2022.pdf

12:30 Lunch

3 Holographic Effective Actions and Bubble Nucleation

A first order phase transition in the early Universe could lead to an observable signal of gravitational waves. When the the sector undergoing the transition is strongly coupled ordinary field theory calculations become significantly harder, but holographic models may be useful to circumvent this issue. We discuss how to obtain an effective action from holographic models capturing the dynamics of the phase transition and estimate the possible gravitational wave production.

Speaker: Carlos Hoyos

hoyos_EffectActGWs.pdf

hoyos.mp4

15:30 Coffee break

4 A Phases of holographic nuclear matter which are phases of crystals of instantons

Nuclear at large number of colors is necessarily in a solid phase. I will explain this fact. In particular holographic nuclear matter takes the form of a crystal of instantons of the flavor group. In this talk I will briefly review the passage from holographic baryonic matter in the Sakai-Sugimoto model to crystansl of instantons. The analysis of the three- dimensional crystal structures and the orientation patterns for the two-body potential that follows from holographic duality will be presented. The outcome of the analysis includes several unexpected results. We perform simulations of ensembles of O(10000) instantons whereby we identify the lattice structure and orientations for the different values of the weight factors of the non-Abelian orientation terms in the two-body potential. The resulting phase diagram is surprisingly complex, including a variety of ferromagnetic and anti-ferromagnetic crystals with various global orientation patterns, and various non-Abelian crystals where orientations have no preferred direction. The latter include variants of face-centered-cubic, hexagonal, and simple cubic crystals which may have remarkably large or small aspect ratios. The simulation results are augmented by analytic analysis of the long-distance divergences, and numerical computation of the (divergence free) energy differences between the non-Abelian crystals, which allows us to precisely determine the structure of the phase diagram.

Speaker: Cobi Sonnenschein

Sonnenschein_Nordita22.pdf

5 New sources of GW

With the advent of GW astronomy, a new exciting window into studying matter has been opened. It is then crucial to perform a search for possible GW sources. In this talk I will present two new sources of GW emission from first order phase transitions: the spinodal instability and phase transitions in neutron star mergers. The former is relevant in the context of cosmology, when bubble nucleation is largely suppressed. The latter has become an exciting possibility in the light of recent results and would produce a potentially detectable signal in the MHz range.

Speaker: Mikel Sanchez Garitaonandia

sanchez Nordita 10-22.pdf

6 Partial deconfinement

In large-$N$ gauge theories, evidence has emerged recently that between confined and deconfined phases a partially-deconfined phase can appear, in which only a subset of colours deconfine. The existence of such a phase has implications for the map between degrees of freedom under gauge/gravity duality and black hole phase diagrams, where a counterpart to the partially-deconfined saddle should be present. We investigate properties of partial deconfinement on the field theory side, first considering the partially-deconfined saddle of large-$N$ pure Yang-Mills theory. Here, the colour degrees of freedom split into confined and deconfined sectors. We argue with the use of numerical simulations that a linear confinement potential is generated in the confined sector, implying the formation of flux tubes, whereas the potential is screened in the deconfined sector and behaves instead according to the perimeter law. Furthermore, we find that the onset of partial deconfinement coincides with the breaking of chiral symmetry breaking, providing an order parameter for the partially-deconfined phase. We conjecture that partial deconfinement is accompanied by a unique signature of global symmetry breaking that can serve as an order parameter. As another, cleaner example of this, we show that CP symmetry breaking coincides precisely with the emergence of the partially-deconfined phase in supersymmetry-broken $\mathcal{N} = 1$ super-Yang-Mills with a theta-angle $\theta = \pi$, for both large finite $N$ and the formal large-$N$ limit. Finally, we discuss consequences of these findings for holography, the QCD crossover, and the internal phase structure of neutron stars.

Speaker: Jack Holden

holden_partial_deconfinement_Nordita.pdf

18:00 Reception

At Proviant (restaurant next to Nordita, same place as lunch)

Thursday, 20 October

7 Holography for QFTs in de Sitter

I will discuss how to set up holography for QFTs in de Sitter by studying AdS gravity coupled to a scalar field in the bulk. The talk will start with a discussion of subtleties regarding the identification of the conformal boundary of asymptotically locally AdS spacetimes. I will then focus on the case the boundary geometry is de Sitter and compute the 1- and 2-point function of the dual QFT for a specific 4-dimensional bulk model.

Speaker: Kostas Skenderis

skenderis.mp4

skenderis_Nordita2022.pdf

10:30 Coffee break

8 Living at the tip of the throat

Warped throats arise generically in string theory flux compactifications, which play a crucial role in the process of moduli stabilisation. Therefore, these non-trivial geometries provide novel avenues to explore cosmological paradigms, such as early and late time acceleration, namely inflation and dark energy. I will discuss recent developments on phenomenological applications of warped throats for cosmological acceleration and 4D gravity.

Speaker: Ivonne Zavala

Talk_Zavala.pdf

zavala.mp4

12:30 Lunch

9 Quantum holographic (in)stability of de Sitter space

Classical gravity coupled to a holographic CFT_4 (matter) is considered. The effect of the quantum dynamics of matter on gravity is studied around de Sitter space. The structure of the graviton propagator is modified and non-trivial poles appear due to matter quantum effects.
The position and residues of such poles are mapped as a function of the relevant parameters, the number of colors $N$ of the CFT$_4$, the two $R^2$ couplings of gravity as well as the curvature of de Sitter The instabilities induced are determined. Such instabilities can be important in cosmology as they trigger the departure from de Sitter space and in some regions of parameters are more important than the well-known scalar instabilities. It is also determined when the presence of such instabilities is unreliable, if the associate scales are larger than the ``species" cutoff of the gravitational theory.

Speaker: Elias Kiritsis

10 Holography and neutrino transport in dense media

The cooling of young neutron stars happens mainly via emission of neutrinos from the core. The modeling of this process requires the knowledge of the neutrino weak interaction rates with the dense QCD matter inside the star. This can be formalized into the calculation of the retarded 2-point correlation function for the chiral currents, which is a strongly coupled problem. The holographic method is one of the only ways of getting analytic insight into most strongly coupled systems. When numerical methods are not available, it is even the best technique we know of to tackle these problems. In particular, lattice QCD is unable to provide results at high baryon density, which is why a lot of effort is put into the study of holographic QCD at high density. In this talk, I will discuss the calculation of the neutrino radiative coefficients in the simplest holographic model that incorporates a finite baryon density. I will explain how the retarded 2-point functions are computed holographically and show some numerical results.

Speaker: Edwan Préau

preau_Nordita_20-10-22.pdf

11 Novel aspects in relativistic hydrodynamics

Recent studies point in the direction that viscosity might be relevant in neutron star mergers. The usual approach to introduce viscosity in relativistic systems, MIS-like theories, has been recently shown to present some limitations. In particular, it presents limitations when dealing with shocks, features present in neutron star mergers. The first-order viscous theory of hydrodynamics proposed by Bemfica, Disconzi, Noronha and Kovtun (BDNK) does not have these limitations and appears as a very good alternative to MIS-like theories. We perform numerical studies of this theory and we use holography to study its regime of applicability by comparing to real-time evolutions of microscopic systems, assessing its accuracy and predictive power.

Speaker: Yago Bea

BDNK_talk_201022_Stockholm_Yago_Bea.pdf

15:30 Free (half) afternoon

18:00 Conference Dinner

At restaurant Kvarnen: https://goo.gl/maps/NzmodknDQj7eiGtP7

Friday, 21 October

12 Quark matter cores in massive neutron stars

I will discuss recent model-independent efforts to discover deconfined matter in the cores of massive neutron stars. Such progress is made possible on one hand by the availability of accurate observational information from neutron-star mass-radius and tidal deformability measurements, and on the other hand by the impressive progress in robust first-principles calculations in chiral effective theory and perturbative QCD. I will review the current status of each of these efforts, and conclude by presenting results from a very recent Bayesian calculation suggesting that quark matter is very likely present inside maximally massive stable neutron stars.

Speaker: Aleksi Vuorinen

vuorinen.mp4

vuorinen Nordita_2022.pdf

10:30 Coffee break

13 Holography of novel QCD phases at high density and neutron stars

The D3/probe D7 system provides a powerful tool for computing the properties of quarks at strong coupling including with temperature, density and chiral symmetry inducing interactions. When applied to neutron stars the system suggests that quark cores are too soft to support neutron stars. We investigate how one might escape that conclusion by looking at the effects of the running coupling and suggesting the possibility of new phases at finite density. A deconfined yet massive quark phase is modelled - if the transition to the high density chirally restored phase is second order then neutron stars remain hard to support. In a model where the transition is first order the phase can be quite distinct from the chirally restored phase and quark cores may be possible. Finally I will discuss a programme to build a new genre of AdS/QCD model based on domain wall fermion techniques that cleanly describes both confinement and the quark condensate - it is progressing towards a new modelling of neutron star equations of state.

Speaker: Nick Evans

evans.mp4

evans NORDITA22.pdf

12:30 Lunch

14 Holographic Floquet on the brane

After reviewing briefly the basics of Floquet engineering, in which quantum systems are manipulated in a controlled way by using time-periodic external fields, we will analyze with holographic techniques the response of a (2+1)-dimensional gauge theory to an external rotating external electric field. This system has a non-equilibrium phase diagram with Floquet condensates in which there is a rotating current with vanishing driving field, as well as Floquet suppression points in which the response to the external perturbation vanishes. Based on 2007.12115 and 2209.03884.

Speaker: Alfonso Ramallo

Ramallo_Stockholm_seminar.pdf

15 Flavored anisotropic black holes

We construct a black hole geometry dual to a (2+1)-dimensional defect in an ambient (3+1)-dimensional gauge theory at non-zero temperature and quark density. The geometry is a solution to the equations of motion of type IIB supergravity with brane sources, a low energy limit of an intersection of stacks of color D3-branes and flavor D5-branes. We consider the case in which the number of D5-branes is large and they can be homogeneously distributed along the directions orthogonal to the defect, creating in this way a multilayer structure. The quark density is generated by exciting a gauge field in the worldvolume of the dynamic brane sources. We study the thermodynamics of the anisotropic black hole and compute the energy density of the dual theory, as well as the pressures and speeds of sound along the directions parallel and orthogonal to the defect. We also calculate transport coefficients in the shear channel, quark-antiquark potentials, and the entanglement entropies for slab subregions. These analyses give us a good overview on how the degrees of freedom are spread, entangled, and behave in this unquenched system in the deconfining phase at strong coupling.

Speaker: Jose Manuel Penin Ascariz

nordita_2022_josemanuelpenin.pdf

15:00 Coffee break