Theoretical Physics

Tree-level open string amplitudes are integrals over the moduli space of n points on the projective line, and their field theory limit is the Cachazo-He-Yuan formula for tr(\Phi^3) amplitudes. Joint work with Freddy Cachazo, Alfredo Guevara and Sebastián Mizera (CEGM) replaces the line by P^(k-1), giving amplitude-like objects whose Feynman diagrams are higher-dimensional polyhedral complexes rather than trees. After reviewing this framework, I will discuss recent progress on new factorization patterns which appear and linear zero-preserving deformations, which produce nonlinear sigma model amplitudes at k=2 by a result of Arkani-Hamed, Cao, Dong, Figueiredo and He, and new factorization behavior at k greater than or equal to 3.

Kirk Public Lecture at the Isaac Newton Institute by Yoshiko Ogata (Kyoto University) on how macroscopic properties of matter emerge from quantum particle interactions and the classification of topological order from an operator-algebraic perspective in mathematical physics.

One of the main achievements of my last four years at Perimeter has been the development and formulation of intrinsic null geometry. This framework has served as a common denominator for the study of the (algebraic) quantization of gravity on null hypersurfaces; connections to quantum-gravity phenomenology for causal diamonds and the derivation of the Verlinde-Zurek fluctuation identity; a complete characterization of the null gravitational phase space; links to asymptotic null infinity; and the related classification of eBMS anomalies. After introducing the basic toolkit of null geometry, I will digress on Carrollian connections and on how the intrinsic geometry is related to an ambient manifold. I will then introduce the null Brown-York stress tensor, which allows the intrinsic gravitational constraints to be recast as conservation laws. Finally, I will briefly retrace the path through the aforementioned applications, with particular emphasis on new and ongoing results.

This talk is about the proposal that (1) quantum states that violate the momentum and Hamiltonian constraints represent instances of time, and (2) time evolution corresponds to the gradual collapse of an initial state toward a diffeomorphism-invariant state, driven by stochastic fluctuations of the lapse and shift. During the wavefunction collapse, the scale factor increases monotonically and thus acts as a clock. Scalar, vector, and tensor gravitons arise as physical excitations. In the long-time limit, the tensor gravitons exhibit emergent unitary dynamics, while the extra modes are damped by the non-unitary dynamics that suppress constraint-violating excitations. I will also comment on possible physical implications of these extra graviton modes.

The Simons Foundation invites proposals to organize new symposium series in mathematics and theoretical physics, including theoretical computer science. Selected series may comprise up to three weeklong meetings with travel, lodging, and meals covered for participants, creating sustained time for collaboration on timely research problems.

RIKEN is recruiting one indefinite-term Research Scientist or Senior Research Scientist for its High-Energy QCD Theory Research Team. Research spans lattice and perturbative QCD, the dynamical properties of strongly interacting matter, and connections to experimental data. The scientist will help establish the team and develop collaborations in Japan. Applicants need a relevant doctorate or equivalent research background and approximately seven years of postdoctoral experience. The position is based at Wako Campus, with an anticipated start after 1 February 2027. Applications must reach RIKEN by 30 September 2026; the official page specifies document uploads and applicant follow-up requirements.

The Simons Foundation invites letters of intent for ambitious collaborations addressing fundamental questions of major importance in mathematics, theoretical physics, or theoretical computer science. Awards support multi-investigator teams across career stages for four years, with up to three new collaborations expected to begin in January 2028.

Develop and apply quantum resource theory for Extended Wigner’s Friend scenarios, where the presence of another observer can affect measurement outcomes. The work involves analytical quantum information and probability theory, together with numerical simulation, and relates to Bell nonlocality. This FAPESP-funded doctoral position is expected to start in March 2027. Apply by 16 November 2026 with a CV, a motivation letter of up to two pages and contact information for two academic referees, following the official advertisement.

Develop and apply quantum resource theory for Extended Wigner’s Friend scenarios, where the presence of another observer can affect measurement outcomes. The work involves analytical quantum information and probability theory, together with numerical simulation, and relates to Bell nonlocality. This FAPESP-funded doctoral position is expected to start in March 2027. Apply by 16 November 2026 with a CV, a motivation letter of up to two pages and contact information for two academic referees, following the official advertisement.

Tree-level open string amplitudes are integrals over the moduli space of n points on the projective line, and their field theory limit is the Cachazo-He-Yuan formula for tr(\Phi^3) amplitudes. Joint work with Freddy Cachazo, Alfredo Guevara and Sebastián Mizera (CEGM) replaces the line by P^(k-1), giving amplitude-like objects whose Feynman diagrams are higher-dimensional polyhedral complexes rather than trees. After reviewing this framework, I will discuss recent progress on new factorization patterns which appear and linear zero-preserving deformations, which produce nonlinear sigma model amplitudes at k=2 by a result of Arkani-Hamed, Cao, Dong, Figueiredo and He, and new factorization behavior at k greater than or equal to 3.

This talk is about the proposal that (1) quantum states that violate the momentum and Hamiltonian constraints represent instances of time, and (2) time evolution corresponds to the gradual collapse of an initial state toward a diffeomorphism-invariant state, driven by stochastic fluctuations of the lapse and shift. During the wavefunction collapse, the scale factor increases monotonically and thus acts as a clock. Scalar, vector, and tensor gravitons arise as physical excitations. In the long-time limit, the tensor gravitons exhibit emergent unitary dynamics, while the extra modes are damped by the non-unitary dynamics that suppress constraint-violating excitations. I will also comment on possible physical implications of these extra graviton modes.

One of the main achievements of my last four years at Perimeter has been the development and formulation of intrinsic null geometry. This framework has served as a common denominator for the study of the (algebraic) quantization of gravity on null hypersurfaces; connections to quantum-gravity phenomenology for causal diamonds and the derivation of the Verlinde-Zurek fluctuation identity; a complete characterization of the null gravitational phase space; links to asymptotic null infinity; and the related classification of eBMS anomalies. After introducing the basic toolkit of null geometry, I will digress on Carrollian connections and on how the intrinsic geometry is related to an ambient manifold. I will then introduce the null Brown-York stress tensor, which allows the intrinsic gravitational constraints to be recast as conservation laws. Finally, I will briefly retrace the path through the aforementioned applications, with particular emphasis on new and ongoing results.