

Abstracts
David Andriot Dark energy and string theory: an update The nature of dark energy, responsible for the observed accelerated expansion of our universe, is one of the biggest puzzles in contemporary physics. String theory, as a candidate fundamental theory, would provide an origin to dark energy in the form of an effective scalar potential V. Getting the right shape for V to match observational constraints is however challenging, and this has led to an important recent activity. In this talk, I will first review the status of classical de Sitter solutions (critical points of V that would give a positive cosmological constant). I will then present possibilities for an asymptotic accelerated expansion, meaning realising dark energy by a field rolling in V towards the asymptotics. In this context, allowing for an open universe (i.e. a negatively curved space) offers important possibilities to string theory cosmological models.
Philippe Brax Screening the dilation?
José Calderon Infante Asymptotic Accelerated Expansion in String Theory? In this talk I will address the question: Is there asymptotic accelerated expansion in string theory? There is Swampland conjecture suggesting a negative answer. It has been tested in a particular asymptotic limit associated to weak string coupling and large volume in Type II string theory compactifications. To go beyond this lamppost, we consider different asymptotic limits of Ftheory flux compactifications on CalabiYau fourfolds. I will discuss a couple of candidates that could feature asymptotic accelerated expansion once the Kähler moduli are stabilized. Based on arXiv:2209.11821 in collaboration with I. Ruiz and I. Valenzuela.
AmirKian KashaniPoor (LPTENS, Paris) Nonperturbative topological string theory on compact CalabiYau threefolds Just like its parent theory, topological string theory is originally defined order by order in its coupling constant, yielding the genus g topological amplitudes F_g associated to a CalabiYau geometry X. The F_g satisfy a recursion relation, the holomorphic anomaly equations. Following up on earlier results proposing to take these equations seriously nonperturbatively, we obtain explicit nonperturbative solutions, and show that they correctly control the large genus asymptotics of the topological string amplitudes. Our study also provides additional evidence that the Stokes constants appearing in the resurgent structure of the theory are closely related to integer BPS invariants.
Patrick Peter (IAP, Paris) The CVOS model for superconducting cosmic string networks A thermodynamical model for describing networks of cosmic string was proposed a while back, with variables an rms velocity and a characteristic length, named Velocity One Scale (VOS). We extended this model to ChargedVOS (or CVOS), which include the superconducting feature expected from a realistic string network. I’ll present this model and its potential cosmological consequences. 
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