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Seminars this week in series RENCTHEO  
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Thursday 15 November 2018, 10:00 at IHP, 201  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Mtheory is currently our best candidate for a theory of everything, but remains mysterious. We know Mtheory has M2 and M5branes. The lowenergy theory on a stack of coincident M2branes is wellunderstood: it is maximally supersymmetric ChernSimonsmatter theory. However, the lowenergy theory on a stack of coincident M5branes remains poorlyunderstood: it is a maximally supersymmetric theory of selfdual strings with zero tension. In this talk I will discuss one type of probe of the M5brane theory, namely selfdual strings with infinite tension. These play a role analogous to Wilson lines in gauge theories, but are twodimensional surfaces rather than lines, and hence are called Wilson surfaces. I will describe holographic calculations of entanglement entropy associated with these infinitetension selfdual strings, from which we extract a key parameter characterizing them, their central charge. This provides a count of the number of massless degrees of freedom living on them, and thus may shed light on some of the fundamental degrees of freedom of Mtheory. 
Thursday 15 November 2018, 11:40 at IHP, 201  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Various swampland conjectures have been put forward in the recent literature to characterize general properties of an effective field theory which can be consistently coupled to quantum gravity. String theory as a framework for quantum gravity allows us to put these conjectures to a quantitative test. Among the earliest of these conjectures is the Weak Gravity Conjecture: It postulates the existence of a set of particles in any quantum gauge theory coupled to gravity whose chargetomass ratio must exceed that of an extremal black hole. In this talk we will verify this and further swampland conjectures in string theory, focussing for simplicity on string compactifications to six dimensions with 8 supercharges, in the vicinity of the weak coupling point of the gauge theory. Our proof of the Weak Gravity Conjecture near the weak coupling point combines various aspects of the Kahler geometry of complex surfaces, arithmetic properties of weak Jacobi forms and BPS invariants on CalabiYau threefolds. Along the way we elucidate the modification of the Weak Gravity Conjecture due to massless scalar fields. We find perfect agreement between the predictions of the modified conjecture and the chargetomass ratio of a set of physical stringy nonBPS states in the theory. Their charges span a sublattice of the full charge lattice, whose index we determine geometrically. 

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