University of Crete HEP Seminars
Small Cosmological Constant in String Theory
| Speaker: | Liam McAllister |
| Institution: | Cornell U. |
| Time: | Tuesday 13 February 2024, 17:15 |
| Venue: | Webinar |
| Abstract: | Why is the vacuum energy in our Universe exponentially small in natural units? Motivated by this difficult problem, we ask a related but cleaner question: do there exist controlled anti-de Sitter solutions of string theory in which the internal space is small but the four-dimensional spacetime is exponentially large compared to the string length? We give an affirmative answer, by explicit construction, in Calabi-Yau compactifications of type IIB string theory. In this talk I will begin with a general overview of the problem of finding vacua in string theory, explain the physical mechanism at work in our solutions, and comment on the prospects for de Sitter solutions along similar lines. |
| Recording: | The recorded talk can be found here. |
Logarithmic corrections in AdS/CFT
| Speaker: | Marina David |
| Institution: | KU Leuven |
| Time: | Tuesday 20 February 2024, 13:15 |
| Venue: | Webinar |
| Abstract: | It is well known that in the semi-classical limit, the entropy of black holes is universally given by the Bekenstein-Hawking formula. There are in fact corrections to this formula arising from higher derivative terms in the gravitational path integral or quantum effects to due matter fields propagating on a fixed gravitational background. Evaluating such corrections is a challenging endeavor, but there is one term, of logarithmic form, that is more accessible. In this talk, I will discuss how logarithmic corrections in four-dimensional AdS gravity theories can be extracted via the heat kernel and the differences between the logarithmic term in asymptotically flat and AdS spacetimes. I will show that our results match the one-loop computations from holographic field theories when it is known, and explain how the logarithmic correction produces constraints on effective field theories coupled to gravity . |
| Recording: | The recorded talk can be found here. |
Tearing down spacetime with quantum disentanglement
| Speaker: | Roberto Emparan |
| Institution: | Barcelona U. and ICREA |
| Time: | Tuesday 27 February 2024, 13:15 |
| Venue: | Webinar |
| Abstract: | If spacetime is holographically built up from the quantum entanglement of microscopic degrees of freedom, it should also be possible to split it apart by disentangling these same degrees of freedom. However, studying this phenomenon with holographic methods reveals a puzzle: the disentangled state appears to keep a large entanglement entropy. I will review this problem and then explain how to resolve it. Interestingly, the solution involves bulk quantum effects of a kind brought to bear on another long-standing enigma in black hole thermodynamics, namely, the entropy of near-extremal Reissner-Nordstrom black holes. . |
| Recording: | The recorded talk can be found here. |
Chaotic and Thermal Aspects in the String S-Matrix
| Speaker: | Diptarka Das |
| Institution: | Indian Inst. Tec. |
| Time: | Tuesday 5 March 2024, 13:15 |
| Venue: | Webinar |
| Abstract: | We compute tree level scattering amplitudes involving more than one highly excited states in bosonic string theory. We use these amplitudes to understand chaotic and thermal aspects of the excited string states lending support to the Susskind-Horowitz- Polchinski correspondence principle. The unaveraged amplitudes exhibit chaos in the resonance distribution as a function of kinematic parameters, which can be described by random matrix theory. Upon coarse-graining these amplitudes exponentiate, and give certain thermal indications. . |
| Recording: | The recorded talk can be found here. |
Gravity, Horizons and Open EFTs
| Speaker: | Clifford P. Burgess |
| Institution: | Perimeter and McMaster U. |
| Time: | Tuesday 12 March 2024, 13:15 |
| Venue: | Webinar |
| Abstract: | Wilsonian effective theories exploit hierarchies of scale to simplify the description of low-energy behaviour and play as central a role for gravity as for the rest of physics. They are useful both when hierarchies of scale are explicit in a gravitating system and more generally for understanding precisely what controls the size of quantum corrections in gravitational systems. But effective descriptions are also relevant for open systems (e.g. fluid mechanics as a long-distance description of statistical systems) for which the `integrating out' of unobserved low-energy degrees of freedom complicate a straightforward application of Wilsonian methods. Observations performed only on one side of an apparent horizon provide examples where open system descriptions also arise in gravitational physics. This chapter describes some early adaptations of Open Effective Theories (i.e. techniques for exploiting hierarchies of scale in open systems) in gravitational settings. Besides allowing the description of new types of phenomena (such as decoherence) these techniques also have an additional benefit: they sometimes can be used to resum perturbative expansions at late times and thereby to obtain controlled predictions in a regime where perturbative predictions otherwise generically fail. |
| Recording: | The recorded talk can be found here. |
A bootstrap study of RG flows in AdS_2
| Speaker: | Edoardo Lauria |
| Institution: | LPENS |
| Time: | Tuesday 19 March 2024, 13:15 |
| Venue: | Webinar |
| Abstract: | For QFTs in AdS the boundary correlation functions remain conformal even if the bulk theory has a scale. This allows one to constrain RG flows with numerical conformal bootstrap methods. In this talk, I will discuss how to apply this idea to study RG flows between two-dimensional CFTs, focusing on deformations of the tricritical and ordinary Ising model. I will present non-perturbative constraints for the boundary correlation functions of these flows and compare them with conformal perturbation theory in the vicinity of the fixed points. I will also discuss a completely general constraint on the sign of the TTbar deformation in two dimensions, and how it emerges from the numerical conformal bootstrap . |
| Recording: | The recorded talk can be found here. |