Found 4 result(s)
Regular Seminar Boris Pioline (LPTHE Jussieu)
at: 14:00 room Zoom  instructions in abstract  abstract: In type II strings compactified on a CalabiYau threefold $X$, the DonaldsonThomas (DT) invariants $\Omega(\gamma,z)$ counting BPS black holes have an intricate dependence on the moduli $z$, due to wallcrossing phenomena. When $X$ is a toric threefold, these indices are related to the DT invariants of a quiver with potential with superpotential, encoded by a brane tiling. I will present a conjecture for the DT invariants for all dimension vectors $d$ in a certain chamber $z_*(d)$ known as the attractor (or selfstability) chamber. In short, "DT invariants all vanish, except when they are known not to." In combination with the attractor flow tree formulae, this conjecture provides an algorithmic way of computing the DT invariants $\Omega(\gamma,z)$ for any $\gamma,z$. The conjecture is supported by a large number of checks, including a successful comparison with the VafaWitten invariants of a Fano surface $S$ when $X$ is the total space of the canonical bundle $K_S$, and with the counting of molten crystals for framed DT invariants in the noncommutative chamber. Based on works with G. Beaujard, J. Manschot and S. Mozgovoy, arXiv:2004.14466 and 2012.14358 Join Zoom Meeting https://zoom.us/j/94029175955?pwd=b1hvVnVxbFZjTmM5bkxaWi93VkpzUT09 Meeting ID: 940 2917 5955 Passcode: 086150 
Regular Seminar Boris Pioline (LPTHE Jussieu and CERN)
at: 14:00 room H503  abstract: BPS states in N=2 gauge theories or string vacua are generically stable but liable to decay across certain codimensionone loci in moduli space. This process is easily understood by viewing BPS states as a bound state of more elementary BPS constituents, described classically by multicentered solutions of the low energy effective action. The semiclassical quantization of the space of such solutions agrees with the wallcrossing formulae derived in the mathematical literature on BPS invariants, providing a physically elementary justification of the latter. Using this intuition, it is possible to express the BPS index, at any point in moduli space, in terms of indices associated to elementary (or singlecentered) constituents. If time permits, I will present evidence for this idea in the case of BPS states described by quiver representations. 
Triangular Seminar Boris Pioline (LPTHE, LPTENS)
at: 15:00 room 410A Physics  abstract: Recently, Ooguri, Strominger and Vafa have proposed to identify the macroscopic BekensteinHawkingWald entropy of extremal charged Black Holes in type II string compactified on a CalabiYau threefold, with the all order microscopic entropy in a specific statistical ensemble. We present a test of this conjecture in the case of 'small' black holes (which have zero BekensteinHawking entropy at tree level, but obtain a nonzero entropy after quantum corrections) using heterotic / type II duality. We find a remarkable agreement to all orders in a class of N=2 and N=4 compactifications. Nevertheless, the OSV proposal misses nonperturbative corrections which are computable on the heterotic side. We comment on possible improvements of this proposal. 
Regular Seminar Boris Pioline (LPTHE, Universite de Paris VI et VII)
at: 16:30 room H503  abstract:
