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Seminars this week in series RENC-THEO
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Thursday 15 November 2018, 10:00 at IHP, 201 RENC-THEO (Rencontres Théoriciennes) hep-th
Andy O'bannon ( University of Southampton ) Wilson Surface Central Charge
Abstract: M-theory is currently our best candidate for a theory of everything, but remains mysterious. We know M-theory has M2- and M5-branes. The low-energy theory on a stack of coincident M2-branes is well-understood: it is maximally supersymmetric Chern-Simons-matter theory. However, the low-energy theory on a stack of coincident M5-branes remains poorly-understood: it is a maximally supersymmetric theory of self-dual strings with zero tension. In this talk I will discuss one type of probe of the M5-brane theory, namely self-dual strings with infinite tension. These play a role analogous to Wilson lines in gauge theories, but are two-dimensional surfaces rather than lines, and hence are called Wilson surfaces. I will describe holographic calculations of entanglement entropy associated with these infinite-tension self-dual 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 M-theory.

Thursday 15 November 2018, 11:40 at IHP, 201 RENC-THEO (Rencontres Théoriciennes) hep-th
Timo Weigand ( CERN ) A Stringy Test of the Weak Gravity Conjecture
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 charge-to-mass 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 Calabi-Yau 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 charge-to-mass ratio of a set of physical stringy non-BPS states in the theory. Their charges span a sublattice of the full charge lattice, whose index we determine geometrically.

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