Event Category: String Seminar

String Seminar:
Tuesdays at 3:40pm on campus

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Abstract: Integrating out degrees of freedom and studying the universality of thus obtained effective field theories is a standard and powerful tool for analyzing QFTs. There are several ways to generalize this procedure to theories without a useful product structure in the Hilbert space, such as ordinary quantum mechanics, the SYK model, or QFTs with global constraints. I will discuss … Read More

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I motivate lattice variants of the Weak Gravity Conjecture (WGC), and show that they have consequences for ultraviolet cutoffs: a parametrically weak gauge coupling requires a quantum gravity scale parametrically below the Planck scale. This result is distinct from older “magnetic WGC” arguments about UV cutoffs, which constrain a “new physics” scale not directly related to the quantum gravity scale. … Read More

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Abstract: A state is said to be Markovian if it fulfil the important condition of saturating the Strong Subadditivity inequality. I will show how the vacuum state of any relativistic QFT is a Markov state when reduced to certain geometric regions of spacetime. For the CFT vacuum, the Markov property is the key ingredient to prove the A theorem (irreversibility … Read More

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In a wide class of cosmological models, a positive cosmological constant drives cosmic evolution toward an asymptotically de Sitter phase. Here we connect this behaviour to the increase of entropy over time, based on the idea that de Sitter is a maximum-entropy state. I will discuss how to prove a cosmic no-hair theorem for Robertson-Walker and Bianchi I spacetimes that … Read More

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Abstract: There are a number of interesting inequalities satisfied by minimal-area surfaces in asymptotically hyperbolic geometries. In the static version of AdS/CFT, these surfaces are interpreted as the entropy of the corresponding boundary regions. This relates quantum information inequalities (e.g. Strong Subadditivity) to geometrical inequalities which can be given simple picture-proofs. Since the dynamical version of AdS/CFT involves Lorentzian geometries, … Read More

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Abstract: I discuss, in an elementary way, special loci in the moduli spaces of string compactifications where the numbers of BPS states jump. In simple examples, these loci are also related to natural objects in number theory. Understanding of these loci leads to new results or conjectures about refined BPS partition functions, attractor black holes, and the counting of flux … Read More

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After reviewing the three objects in the title I will argue that they are closely related. In more details: study of effective string theory has lead us to consider 2D quantum field theories with a novel UV asymptotic behavior, dubbed asymptotic fragility. This UV behavior can be introduced by certain gravitational dressing of scattering amplitudes in two dimensions. Gravitational dressing … Read More

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Abstract: Non-extremal black holes, which emit thermal Hawking radiation, have two horizons: the event horizon or outer horizon and the Cauchy horizon or inner horizon. Surprisingly, for a broad class of solutions to the Einstein equations, the product of the areas of the inner and outer horizons is the square of the area of the horizon of the zero temperature … Read More

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Abstract: I will discuss a new proposal for multiverse analysis based on computational complexity. By defining a cosmology as a space-time containing a vacuum with specified properties (for example small cosmological constant) together with rules for how time evolution will produce the vacuum, we can associate global time in a multiverse with clock time on a supercomputer which simulates it. … Read More