[Seminar] "Vacuum decay rate in the standard model and beyond" by Dr. Yutaro Shoji

Speaker: Dr. Yutaro Shoji from Nagoya University

Abstract:
The electroweak vacuum is not absolutely stable in the standard model and various models beyond the standard model. This is due to an appearance of another deeper vacuum, into which the electroweak vacuum can decay. The decay proceeds through quantum tunneling and the rate is expressed with an exponential suppression factor and a pre-factor. The suppression factor has been calculated in many papers, but a naive dimensional analysis has been usually adopted for the pre-factor.

We have pointed out that such an evaluation can suffer from large quantum corrections and it is important to calculate the pre-factor as well.

To calculate the pre-factor, we had problems in a gauge sector; its gauge invariance is not explicitly shown, and there appear zero modes, which we could not deal with.

We have solved these problems and made it possible to determine vacuum decay rates precisely.

As applications, we analyzed the decay rates in the standard model and its fermionic extensions. We also provide a public code, which can be used for models that exhibit classical scale invariance at a high energy scale.

QG group meeting: Fluid/gravity correspondence

This is the weekly QG group meeting.

Speaker: Vyacheslav  Lysov 

Title: Fluid/Gravity Correspondence 

Journal club seminar: Geometry of Complexity

Discussion  by Vyacheslav Lysov on Geometry of Complexity.

QG group meeting: null hypersurface geometry

QG group meeting
Speaker: Yasha Neiman
Title: Introduction to the geometry of null hypersurfaces

[Seminar] "TOPOLOGICAL DEFECTS, DEFORMED LATTICES AND SPONTANEOUS SYMMETRY BREAKING" by Dr. Vincenzo Vitagliano

Speaker: Dr. Vincnezo Vitagliano from Keio University

Abstract:
External conditions have a dramatic impact on the way dynamical symmetry breaking occurs. I will review some recent (and some less recent) results of symmetry breaking in curved spacetime. Flirting with the contemporary interest toward 2D engineered material, I will then move on potential applications on geometrically deformed lattices. In a curved background, the natural expectation is that curvature works toward the restoration of an internal symmetry. I will show instead that, for topological defects, the competing action of the locally induced curvature and of boundary conditions generated by the non-trivial topology allows configurations where symmetries can be spontaneously broken close to the core.

[Seminar] "Constraining Quantum Gravity from the Bottom-up" by Dr. Scott Melville

Gravity on large scales is relatively well understood. For galaxies, planets and apples: we have Einstein’s General Relativity with which to make accurate predictions. But on small scales, where quantum mechanics becomes important, gravity is more difficult to understand, and as a result we lack precise descriptions of various natural phenomena (such as black holes).

One way to make progress in in our search for quantum gravity is to start from the large scale theory we know and love (at the ‘bottom’), and look for ways in which it may be modified and improved as we zoom in to smaller scales (going ‘up’ to a more fundamental theory).

Recent progress in ‘Effective Field Theory’ may shed some light on the connections between large and small scale physics. By exploiting certain physical properties of scattering probabilities (e.g. that they are unitary, causal and local), one can derive an infinite number of constraints which any large scale theory must satisfy in order to admit a sensible small scale completion.

In this talk, I will provide an overview of these new ‘positivity constraints’, and discuss their implications for quantum gravity.        

QG group meeting - the complex action of GR and black hole entropy

QG group meeting
Speaker: Yasha Neiman
Title: "The complex action of GR and black hole entropy"

[Seminar] "Solitons, Gravity, Gravitating Solitons and Holography" by Dr. Sven Bjarke Gudnason

This talk will take as a starting point the Skyrmions as baryons in large-N QCD. It is further assumed that at high density, the sextic term in derivatives becomes dominant at some large density. This assumption is based on the observation that the term behaves like a perfect fluid, which is welcome for nuclear matter at large density – an environment suitable for the studies of neutron stars. With very large masses and compact radii, neutron stars become the closes known stable objects to the critical line of gravitational collapse. With some phenomenological motivation in mind, we consider the possibilities of finding exact analytic solutions to a system which is approximated by the sextic derivative term and a potential; this system is called the BPS-Skyrme model. We find a condition for when the gravitating soliton equations can be solved exactly and deduce the phenomenological implications. We furthermore find that this system has the peculiarity of not having stable black holes, meaning that the soliton cannot become scalar hair of a black hole. This is somewhat surprising, because the Skyrme soliton with a fourth-order derivative term can become stable black hole hair. We write down a class of models with higher-order derivative terms and find 2 new models that can sustain stable hair and 2 new that cannot.

Finally, we consider the problem of the classical binding energies of the Skyrmions, which are far too large compared to nuclei and explain a solution to this problem based on holography. Interestingly the solution from holography relates the baryon to the instanton of a 5-dimensional theory and the moduli of the instanton become massive modes in the Skyrmion. These modes in addition to the zero modes of the Skyrmion are expected to describe the spectra of nuclei.

QG group meeting: Integrability and the quantum inverse scattering method

QG group meeting
Speaker: Blaithin Power
Title: Integrability and the quantum inverse scattering method

Conformal Bootstrap lecture series

Conformal bootstrap lecture series organized by Aryeh Fortinsky