# Observations with LHAASO-1/2 and the Construction Status

**This is a joint seminar with the Institute of High Energy Physics in Beijing.**

The idea that low energy fields such as Gravitons or Axions can be thought of as composite particles has been entertained since a long time. We revisit this idea motivated by the AdS/CFT correspondence. We focus in the case of axions and show that hidden sectors coupled to SM fields may provide an emergent axionic field that is a composite of the hidden fields (instanton density). This is a more general phenomenon beyond holographic theories. We study the general properties of such an "emergent axion", without a PQ symmetry. The construction goes beyond

Inflation, an era of accelerated expansion of the universe prior to the radiation phase, constitutes the paradigm of primordial cosmology. Within this paradigm, the simplest single-field slow-roll models economically explain all curent data. However, the sensitivity of inflation to Planck scale physics, and the fact that ultraviolet completions of inflation invariably involve extra fields coupled to the inflaton, indicate that these models constitute at best a phenomenological description that emerges from a more realistic physical framework.

The observed accelerated expansion of the Universe opens up

the possibility that general relativity is modified on cosmological

scales. While this has motivated the theoretical study of many

alternative theories that will be tested by the next generation of

cosmic large-scale structure surveys, I will show that the recent

observations of gravitational waves by LIGO/Virgo has dramatic

consequences on these theories.

Mergers of compact objects, such as black holes and neutron stars, have been nicknamed *standard sirens*, by analogy with electromagnetic standard candles, because their waveform directly gives access to their distance. When an electromagnetic counterpart is observed, such sources thus allow us to construct a *Hubble diagram*, just as supernovae. Recently, the gravitational-wave Hubble diagram has been argued to be a key probe of alternative theories of gravity, such as *Horndeski models*.

Asymptotically flat spacetimes admit both supertranslations and Lorentz transformations as asymptotic symmetries known as BMS symmetries. Furthermore, they admit super-Lorentz transformations, namely superrotations and superboosts, as outer symmetries associated with super angular momentum and super-center-of-mass charges. In this talk, we present the flux-balance laws for all such (extended) BMS charges in terms of radiative multipole moments at future null infinity.

n this talk I will present some recent results on instabilities of anti-de Sitter flux compactifications in effective field theories arising from non-supersymmetric string models, namely the USp(32) and U(32) orientifold models and the SO(16) x SO(16) heterotic string. We focus on non-perturbative instabilities, framing the vacua in terms of brane stacks, analyzing their back-reacted geometry and reproducing AdS its near-horizon limit.

I will present a review on D-brane realizations of the Standard Model and their phenomenological consequences.

First, I will provide the basic ingredients of D-brane (open string) models which are useful for model building.

Next, I will use them in order to embed the Standard Model in open string vacua.

Finally, I will discuss new gauge fields and new matter particles which are predictions of the D-brane realizations of the Standard Model described above.

This one-day workshop will bring together theorists working on the AdS/CFT correspondence, nuclear physics, and General Relativity for an interdisciplinarly exchange aimed at developing a consistent holographic picture of QCD matter at high density, from model building to the description of compact objects and observation via gravitational wave signals. Invited speakers include: Umut Gursoy (Utrecht U); Matti Jarvinen (Utrecht U. and Tel Aviv U.); Niko Jokela (Helsinki U.); Micaela Oertel (LUTH); Eric Gourgoulhon (LUTH).

Programme: