Centre de Physique Théorique


Juin 2017

Vendredi 2 juin 14:00-15:00, Amphi 5 du CPT

Consistent modifications of gravity

Lavinia Heisenberg

I will discuss different attempts to modify the gravitational interactions in the UV and IR together with their underlying motivations. For the IR modifications on the other hand, I will discuss the developments and progress made in massive gravity, scalar-tensor and vector-tensor theories and emphasise their common
and distinctive features. Among the UV modifications I will pay special attention to the Born-Infeld inspired
gravity theories and explain their dominant features.

Jeudi 8 juin 14:00-15:00, Amphi 5 du CPT


Peter Hislop, (Department of Mathematics, University of Kentucky, Etats-Unis)


We prove that the local eigenvalue statistics for Schrödinger operators with random point interactions on $\mathbb R^d$, for $d=1,2,3$ is Poissonian in the localization regime. This is the first example of eigenvalue statistics for multi-dimensional random Schrödinger operators in the continuum.
The special structure of the point interactions facilitates the proof of the Minami estimate.
This is joint work with W. Kirsch and M. Krishna.

Mercredi 14 juin 15:30-16:30, Amphi 5 du CPT

Quantum reference frames, quantum asymmetry, and quantum information

Robert W. Spekkens (Perimeter Institute for Theoretical Physics)

The asymmetry properties of a quantum state specify how and to what extent a given symmetry is broken by the state. If implementing symmetric dynamics is easy while implementing dynamics that break the symmetry is hard or impossible, then asymmetry becomes a resource (analogous to the resource of entanglement). It is the key resource in the field of quantum metrology because correlating reference frames (i.e., synchronizing clocks, aligning gyroscopes, etcetera) is a problem of distributing information about a group and the measure of how well a state can achieve such an alignment is a measure of its asymmetry. It is also significant for understanding the consequences of symmetric dynamics : measures of the asymmetry of a state provide new constraints on the possible state evolutions, constraints that supplement those imposed by Noether’s theorem. Formalizing the notion of asymmetry also provides perspective on some conceptual puzzles, such as an apparent failure of Curie’s principle in the quantum realm. A pervading theme of the talk will be the invasion of physics by information theory.

Vendredi 16 juin 11:30-12:30, Amphi 5 du CPT

R_K and neutrino mixing in a class of U(1)_X models.

Disha Bhatia

We take a generalized approach for model building to explain the flavour anomaly, R_K.
In the process we determine various U(1)_X symmetries which addresses R_K by taking hints from the neutrino sector. These models may be tested at the colliders with few fb^-1 of the total integrated Luminosity.

Mercredi 21 juin 11:00-12:00, Amphi 5 du CPT

Fractional diffusion in finite size domains

Diego del-Castillo-Negrete (ORNL, US Department of Energy science, Etats-Unis)


We address two problems in the study of fractional diffusion in finite size domains. The first problem focusses on the physics limitations of the standard fractional diffusion model based on Levy flights driven by alpha-stable distributions. It is shown that tempered Levy distributions, and their corresponding tempered fractional diffusion operators, offer a more realistic model to incorporate finite size effects. The second problem deals with the incorporation of physically meaningful and mathematically well-posed boundary conditions in fractional diffusion. The standard fractional diffusion model in a bounded domain is in general singular. Our approach is based on the regularization of the singularities at the boundary. Following the formal construction of the regularized fractional diffusion model we present numerical solutions.

Mercredi 21 juin 14:00-15:00, Amphi 5 du CPT

Covariant Poisson Bracket for Extended MHD and Hamiltonian 3+1 decomposition

George Miloshevich (Department of Physics, University of Texas, Etats-Unis)


In astrophysical and other applications, plasma is often in a
collisionless state, where resistive and viscous effects are not
important on the time/spatial scales of interest. Extended MHD (XMHD) is
a one-fluid Hamiltonian theory endowed with 2-fluid effects, which are
thought to be important for the formation of relativistic jets from
active galactic nuclei, micro-quasars, and gamma-ray bursts. We
consider the relativistic [1] generalization of XMHD, obtained via an
action principle (AP). We describe covariant Poisson bracket in terms
of Eulerian variables, with constraints implemented via the degeneracy
of the Poisson bracket.

Upon taking appropriate limits, AP leads to relativistic Hall MHD.
While nonrelativistic HMHD does not have a direct mechanism for
collisionless reconnection, relativistic HMHD allows the violation of
the frozen-in magnetic flux condition via an electron thermal inertia
effect. An alternative frozen-in flux has also been found in a manner
similar to that for nonrelativistic IMHD. The scale length of the
collisionless reconnection is shown to correspond to the reconnection
layer width estimated by the Sweet-parker model [2].

Finally we perform a 3+1 decomposition. This results in a bracket that
is more general than the one derived earlier by Abdelhamid at al. [3],
as it is valid for arbitrary electron to ion mass ratio and can be
applied, for instance, to electron-positron plasmas. Further, the
Casmir invariants one obtains this way turn out to be precisely the
generalized helicities, which topologically constrain possible evolution
of the plasma.

[1] Y. Kawazura, G. Miloshevich, P. J. Morrison, Phys. Plasmas 24,
022103 (2017)

[2] L. Comisso and F. A. Asenjo, PRL 113, 045001 (2014)

[3] H. M. Abdelhamid, Y. Kawazura, and Z. Yoshida, J. Phys.A 48, 235502

Mercredi 28 juin 11:00-12:00, Amphi 5 du CPT

Problèmes inverses d’aimantation et paléomagnétisme

Laurent Baratchart (INRIA, Sophia Antipolis)

Résumé On discutera les (...)

Résumé On discutera les problèmes relatifs à l’inversion d’une distribution d’aimantation à partir du champ magnétique qu’elle engendre à quelque distance de son support. On discutera en particulier les questions de non-unicité et celles relatives à l’estimation du moment, dans des géométries planes, puis plus générales. Ceci sera l’occasion d’introduire une décomposition vectorielle de Hardy-Hodge. Ces problèmes apparaissent en paléomagnétisme, on exposera également ces motivations.

Mercredi 28 juin 14:00-15:30, Amphi 5 du CPT

Absence of eigenvalues of Schrödinger operators with complex potentials

David Krejcirik (Department of Mathematics, Czech Technical University, Prague, République tchèque)


We prove that the spectrum of Schrödinger operators in three dimensions
is purely continuous and coincides with the non-negative semiaxis
for all potentials satisfying a form-subordinate smallness condition.
By developing the method of multipliers,
we also establish the absence of point spectrum for
electromagnetic Schrödinger operators in all dimensions
under various alternative hypotheses,
still allowing complex-valued potentials with critical singularities.
This is joint work with Luca Fanelli and Luis Vega.

Vendredi 30 juin 14:00-15:00, Amphi 5 du CPT


Elena Giusarma (Berkeley)