Dan Kapec (Harvard): Quasinormal Corrections to Near-Extremal Black Hole Thermodynamics | 1/22/2025
Recent work on the quantum mechanics of near-extremal non-supersymmetric black holes has identified a characteristic scaling of the low temperature black hole partition function. This result has only been derived using the path integral in the near-horizon region and relies on many assumptions. We discuss how to derive the scaling for the near-extremal rotating BTZ black hole from a calculation in the full black hole background using the Denef-Hartnoll-Sachdev (DHS) formula, which expresses the 1-loop determinant of a thermal geometry in terms of a product over the quasinormal mode spectrum. We also derive the spectral measure for fields of any spin in Euclidean BTZ and use it to provide a new proof of the DHS formula and a new, direct derivation of the BTZ heat kernel. The computations suggest a path to proving the scaling for the asymptotically flat 4d Kerr black hole.
Zach Weiner (Perimeter): Detectable dark photon dark matter | 1/29/2025
Ultralight dark photons are dark matter candidates supported by a burgeoning direct-detection program searching for their kinetic mixing with the ordinary photon. A dark photon's dynamics in the early Universe, however, can easily breach the validity of the low-energy effective theory for a massive vector field, with disastrous consequences for its viability as a dark matter candidate. I will assess the extent to which the direct detection of dark photon dark matter would require a nonminimal dark sector. Specifically, I will survey the detection prospects of known dark photon production mechanisms, outline model-building strategies that are viable in expanded parameter space, and discuss complementary cosmological and astrophysical signatures that could probe the physics responsible for dark photon production.
Rapheala Wutte (Arizona State): Hyperbolic Mass in 2+1 Dimensions | 2/05/2025
Solutions to general relativity with a negative cosmological constant have received significant attention due to the conjectured AdS/CFT correspondence, a particularly well-understood example of which is exhibited in 2+1 dimensions. After reviewing known vacuum solutions to general relativity with a negative cosmological constant in 2+1 dimensions, I will present a gluing theorem for the corresponding vacuum general-relativistic initial data sets. By gluing two given vacuum initial data sets at infinity, we obtain new vacuum initial data sets. I will sketch the derivation of the mass formulae of the resulting manifolds. For the case of the BTZ black hole, by invoking usual black hole thermodynamics, our mass formulae may be interpreted as entropy formulae. Our gluing theorem yields complete manifolds with any mass aspect function, which are smooth except for one conical singularity.
Claudio Andrea Manzari (UC Berkeley): Strong CP and Flavor | 2/12/2025
I will discuss a class of multi-Higgs doublet extensions of the Standard Model that solves the strong CP problem with profound consequences for the flavor sector. A flavor symmetry, G, that acts on Higgs and quark fields is a key feature of these theories. CP and G are only softly broken in the scalar potential, so that for certain choices of G charges, the strong CP parameter is zero at tree-level. I will then discuss radiative corrections in this class of theories, as well as the contribution from higher-dimensional operators and the connections with the hierarchies observed in quark masses and mixing angles.
Elliott Gesteau (Caltech/KITP): Algebras, ergodicity, and the emergence of causality | 2/26/2025
Given a general many-body quantum system, how can we diagnose whether a holographic causal structure emerges as its number of degrees of freedom goes to infinity? In this talk, I will explain which general tools the language of von Neumann algebras provides us with to address this question. In particular, I will show that a sharp horizon structure emerges in the dual of N=4 SYM theory at finite 't Hooft coupling, which allows to make sense of causality at nonzero string length in string theory. I will also elaborate on an intriguing interplay between the algebraic results we will encounter and the theory of chaos in classical and quantum dynamical systems.
Adam Ball (Perimeter): Dynamical Edge Modes and Entanglement in Gauge Theory | 3/12/2025
Standard approaches to entanglement entropy assume a factorization of the Hilbert space along subregions. All QFTs have UV obstructions to this factorization, requiring regularization. Gauge theories have additional, global/IR obstructions. The treatment in the existing literature for entanglement entropy in gauge theories involves a by-hand path integral over non-dynamical superselection sectors, labeled by edge modes. I will describe a new approach that treats the edge modes dynamically, incorporating them into a single phase space, and allows the entanglement to be written as a genuine thermal trace on a subregion. I will provide checks in all dimensions by comparing with recent results on sphere partition functions.
Yue Zhao (Utah): Search for dark photons with synchronized quantum sensor network | 3/19/2025
Ultralight dark photons constitute a well-motivated candidate for dark matter. A coherent electromagnetic wave is expected to be induced by dark photons when coupled with Standard-Model photons through kinetic mixing mechanism, and should be spatially correlated within the de Broglie wavelength of dark photons. I will report the first search for correlated dark-photon signals using a long-baseline network of 15 atomic magnetometers, which are situated in two separated meter-scale shield rooms with a distance of about 1700 km. Both the network's multiple sensors and the shields large size significantly enhance the expected dark-photon electromagnetic signals, and long-baseline measurements confidently reduce many local noise sources. Using this network, we constrain the kinetic mixing coefficient of dark photon dark matter over the mass range 4.1 feV-2.1 peV, which represents the most stringent constraints derived from any terrestrial experiments operating over the aforementioned mass range.
Pratikh Rath (UC Berkeley): Geometric Entropies and their Hamiltonian Flow | 4/02/2025
The geometric entropy is a localized contribution to the entropy obtained using Euclidean gravity methods. In this talk, I will discuss the Hamiltonian flow generated by the geometric entropy operator in general theories of gravity using Lorentzian methods of the Peierls/Poisson brackets. I will discuss examples with higher derivative corrections to illustrate the general features of the geometric flow. In the context of AdS/CFT, I will discuss the connection to modular flow.
Soumangsu Chakraborty (OSU): Effective $AdS_3/CFT_2$; Life is simpler without black holes | 4/09/2025
The holographic dual to string theory in $AdS_3 x N$ has always been a fundamental question in high-energy theoretical physics. To this day, we don't know the answer to this question in full generality. In this talk, I'll propose an effective holographic dual to type IIB string theory in $AdS_3 x N$ in the presence of pure NS-NS flux. The dual boundary CFT takes the form of a p-fold symmetric product of $(R_\phi \times N)$ deformed by a $\phi$-dependent $Z_2$-twisted marginal operator. I'll explain how an exact worldsheet computation allows us to identify this marginal operator.
When the radius of $AdS_3$, $R_{ads}$, is sub-stringy, the CFT spectrum doesn't contain neither a normalizable vacuum nor the BTZ black hole states. The proposed holographic duality in this case is an exact one. On the other hand, when $R_{ads}/l_s >1$, the full boundary CFT does have a normalizable vacuum and the BTZ black hole states at high energies. The proposed duality in this case is an effective one and holds only for the perturbative string states in the spectrum. Finally, I'll quote some of the checks that have been performed to test this duality.
