Of the seminar talks we have titles for, so far, the first two are by Pietro Donà and by a two-person team of Marc Geiller and Simone Speziale. Here are a few relevant papers one might glance at to get an idea of the topic:
http://arxiv.org/abs/1311.2898
Matter matters in asymptotically safe quantum gravity
Pietro Donà, Astrid Eichhorn, Roberto Percacci
(Submitted on 12 Nov 2013, last revised 2 Dec 2013)
We investigate the compatibility of minimally coupled scalar, fermion and gauge fields with asymptotically safe quantum gravity, using nonperturbative functional Renormalization Group methods. We study d=4,5 and 6 dimensions and within certain approximations find that for a given number of gauge fields there is a maximal number of scalar and fermion degrees of freedom compatible with an interacting fixed point at positive Newton coupling. The bounds impose severe constraints on grand unification with fundamental Higgs scalars. Supersymmetry and universal extra dimensions are also generally disfavored. The standard model and its extensions accommodating right-handed neutrinos, the axion and dark-matter models with a single scalar are compatible with a fixed point.
22 pages, 18 figures, 4 tables
http://arxiv.org/abs/1112.1965
Testing the imposition of the Spin Foam Simplicity Constraints
Marc Geiller, Karim Noui
(Submitted on 8 Dec 2011, last revised 30 May 2012)
We introduce a three-dimensional Plebanski action for the gauge group SO(4). In this model, the B field satisfies quadratic simplicity constraints similar to that of the four-dimensional Plebanski theory, but with the difference that the B field is now a one-form. We exhibit a natural notion of "simple one-form", and identify a gravitational sector, a topological sector and a degenerate sector in the space of solutions to the simplicity constraints. Classically, in the gravitational sector, the action is shown to be equivalent to that of three-dimensional first order Riemannian gravity. This enables us to perform the complete spin foam quantization of the theory once the simplicity constraints are solved at the classical level, and to compare this result with the various models that have been proposed for the implementation of the constraints after quantization. In particular, we impose the simplicity constraints following the prescriptions of the so-called BC and EPRL models. We observe that the BC prescription cannot lead to the proper vertex amplitude. The EPRL prescription allows to recover the expected result when, in this three-dimensional model, it is supplemented with additional secondary second class constraints.
30 pages. 18 figures, Class.Quant.Grav. 29 (2012) 135008
http://arxiv.org/abs/1112.1961
Spin Foams and Canonical Quantization
Sergei Alexandrov, Marc Geiller, Karim Noui
(Submitted on 8 Dec 2011, last revised 19 Aug 2012)
This review is devoted to the analysis of the mutual consistency of the spin foam and canonical loop quantizations in three and four spacetime dimensions. In the three-dimensional context, where the two approaches are in good agreement, we show how the canonical quantization à la Witten of Riemannian gravity with a positive cosmological constant is related to the Turaev-Viro spin foam model, and how the Ponzano-Regge amplitudes are related to the physical scalar product of Riemannian loop quantum gravity without cosmological constant. In the four-dimensional case, we recall a Lorentz-covariant formulation of loop quantum gravity using projected spin networks, compare it with the new spin foam models, and identify interesting relations and their pitfalls. Finally, we discuss the properties which a spin foam model is expected to possesses in order to be consistent with the canonical quantization, and suggest a new model illustrating these results.
79 pages, SIGMA 8 (2012), 055
Spot checks on the current pop-string sales ranks:
15 Jan elegant, fabric, grand, hidden, e-elegant (15679+16482+16697+23981+31250)/5=20817.8
16 Jan fabric, grand, elegant, e-elegant, hidden (12104+14902+16896+21828+25208)/5=18187.6
