Author Archives: gmoschidis

Yakov Shlapentokh-Rothman (Princeton)

The APDE seminar on Monday, 05/18, will be given by Yakov Shlapentokh-Rothman online via Zoom from 4:10 to 5pm. To participate, email Georgios Moschidis (gmoschidis@berkeley.edu) or Thibault de Poyferré (tdepoyfe@math.berkeley.edu).

Title: Naked Singularities for the Einstein Vacuum Equations: The Exterior Solution.

Abstract: We will start by recalling the weak cosmic censorship conjecture. Then we will review Christodoulou’s construction of naked singularities for the spherically symmetric Einstein-scalar field system. Finally, we will discuss joint work with Igor Rodnianski which constructs spacetimes corresponding to the exterior region of a naked singularity for the Einstein vacuum equations.

Albert Ai (UW Madison)

The APDE seminar on Monday, 05/11, will be given by Albert Ai online via Zoom from 4:10 to 5pm. To participate, email Georgios Moschidis (gmoschidis@berkeley.edu) or Thibault de Poyferré (tdepoyfe@math.berkeley.edu).

Title: Two dimensional gravity waves at low regularity.

Abstract: In this talk, we will consider the low regularity well-posedness problem for the two dimensional gravity water waves. This quasilinear dispersive system admits an interesting structure which we exploit to prove a new class of energy estimates, which we call balanced cubic estimates. This yields a key improvement over the earlier energy estimates of Hunter-Ifrim-Tataru. These results allow us to significantly lower the regularity threshold for local well-posedness, even without using dispersive properties. This is joint work with Mihaela Ifrim and Daniel Tataru.

Sung-Jin Oh (UC Berkeley)

The APDE seminar on Monday, 04/27, will be given by Sung-Jin Oh online via Zoom from 4:10 to 5pm. To participate, email Georgios Moschidis (gmoschidis@berkeley.edu) or Thibault de Poyferré (tdepoyfe@math.berkeley.edu).

Title: Strong cosmic censorship and generic mass inflation for charged black holes in spherical symmetry.

Abstract: In this talk, I will first review a previous work with J. Luk, in which the C2-formulation of the strong cosmic censorship is proved for the Einstein-Maxwell-(real)-Scalar Field system in spherical symmetry for two-ended asymptotically flat data. More precisely, it was shown that a “generic” class of data for this model gives rise to maximal future developments which are future C2-inextendible. In the second part of the talk, I will present a new, complementary theorem (also joint with J. Luk) that for a further “generic” subclass of such data, the Hawking mass blows up identically along the Cauchy horizon. This result confirms, rigorously and unconditionally, the mass inflation scenario of Poisson-Israel and Dafermos for the model at hand.

Daniel Tataru (UC Berkeley)

The APDE seminar on Monday, 04/20, will be given by Daniel Tataru online via Zoom from 4:10 to 5pm. To participate, email Georgios Moschidis (gmoschidis@berkeley.edu) or Thibault de Poyferré (tdepoyfe@math.berkeley.edu).

Title: Multisolitons and their stability in 1-d cubic NLS.

Abstract: The aim of this talk is first to describe the multisoliton manifold for the 1-d cubic NLS flow, and then to consider their stability. This continues recent work, joint with Herbert Koch, on energy estimates for this and other related integrable evolutions.

Wolf-Patrick Düll (Stuttgart)

The APDE seminar on Monday, 03/02, will be given by Wolf-Patrick Düll in Evans 939 from 4:10 to 5pm.

Title: Validity of the nonlinear Schrödinger approximation for the two-dimensional water wave problem with and without surface tension.

Abstract: We consider the two-dimensional water wave problem in an infinitely long canal of
finite depth both with and without surface tension. In order to describe the evolution
of the envelopes of small oscillating wave packet-like solutions to this problem the
Nonlinear Schrödinger equation can be derived as a formal approximation equation.
The rigorous justification of the Nonlinear Schrödinger approximation for the water
wave problem was an open problem for a long time. In recent years, the validity
of this approximation has been proven by several authors only for the case without
surface tension.
In this talk, we present the first rigorous justification of the Nonlinear Schrödinger approximation for the two-dimensional water wave problem which is valid for the
cases with and without surface tension by proving error estimates over a physically
relevant timespan in the arc length formulation of the water wave problem. Our
error estimates are uniform with respect to the strength of the surface tension, as the
height of the wave packet and the surface tension go to zero.

Mihai Tohaneanu (University of Kentucky)

The APDE seminar on Monday, 03/09 will be given by Mihai Tohaneanu in Evans 939 from 4:10 to 5pm.

Title: Local energy estimates on black hole backgrounds.

Abstract: Local energy estimates are a robust way to measure decay of solutions to linear wave equations. I will discuss several such results on black hole backgrounds, such as Schwarzschild, Kerr, and suitable perturbations converging at various rates, and briefly discuss applications to nonlinear problems. The most challenging geometric feature one needs to deal with is the presence of trapped null geodesics, whose presence yield unavoidable losses in the estimates. This is joint work with Lindblad, Marzuola, Metcalfe, and Tataru.

Mihaela Ifrim (UW Madison)

The APDE seminar on Monday, 02/24 will be given by Mihaela Ifrim in Evans 939 from 4:10 to 5pm.

Title: Almost global well-posedness for quasilinear strongly coupled wave-Klein-Gordon systems in two space dimensions.

Abstract: We prove almost global well-posedness for quasilinear strongly coupled wave-Klein-Gordon systems with small and localized data in two space dimensions. We assume only mild decay on the data at infinity as well as minimal regularity. We systematically investigate all the possible quadratic null form type quasilinear strong coupling nonlinearities, and provide a new, robust approach for the proof.

CANCELLED: Johannes Sjöstrand (IMB)

The APDE seminar on Monday, 03/16 will be given by Johannes Sjöstrand in Evans 939 from 4:10 to 5pm.

Title: Resonances over a potential well in an island.

Abstract: Recent work with M. Zerzeri. Let V : R^n → R be a sufficiently analytic potential which tends to 0 at infinity. Assume that for an E > 0 we have V^{-1}(]- ∞ ,E[)=U(E) ⊔ S(E), where U(E)S(E) = ∅ , with U(E) connected and bounded (the well) and S(E) connected (the sea). The distribution of the resonances of -h^2 Δ + V near E has been thoroughly studied since more than 30 years. If we increase E a natural scenario is that the decomposition persists until the closures of U(E) and S(E) intersect at a critical energy E = E_0. Under some natural assumptions we show that near E_0 most of the resonances are close to the real axis and obey a Weyl law. In one dimension there are more detailed results (Fujiie-Ramond ’98).

Dean Baskin (TAMU)

The APDE seminar on Monday, 11/18 will be given by Dean Baskin in Evans 939 from 4:10 to 5pm.

Title: Asymptotics of the radiation field on cones

Abstract:
Radiation fields are rescaled limits of solutions of wave equations near “null infinity” and capture the radiation pattern seen by a distant observer.  They are intimately connected with the Fourier and Radon transforms and with scattering theory.  We consider the wave equation on a product cone and show that the associated radiation field has an asymptotic expansion; the exponents seen in this expansion are the resonances of the hyperbolic cone with the same link.  This talk is based on joint work with Jeremy Marzuola (building on prior work with Andras Vasy and Jared Wunsch).

Jared Wunsch (Northwestern)

The APDE seminar on Monday, 11/04 will be given by Jared Wunsch in Evans 939 from 4:10 to 5pm.

Title: A tale of two resolvent estimates

Abstract:
I will discuss two new results concerning the best of resolvent estimates and the worst of resolvent estimates.  In the former, case, that of nontrapping obstacles or metrics, we have obtained (in joint work with Galkowski and Spence) optimal, dynamically determined, constants in the standard non-trapping estimate for the (chopped off) resolvent.  In the latter case, that of obstacles or metrics that may have very strong trapping, I will discuss joint work with Lafontaine and Spence that shows the estimates to be a far, far better thing than you might have expected, provided you omit a small set of frequencies from consideration.