PACTS 2018: Particle, Astroparticle and Cosmology Tallinn Symposium

Session

Higher derivatives Gravity and Ghosts

22 Jun 2018, 08:30

Conference Hall (Estonian Academy of Sciences)

62. The Case against Ghosts in Fundamental Theory

Prof. Richard Woodard

22/06/2018, 09:00

I review the theorem of Ostrogradsky and discuss some of the common misconceptions concerning kinetic energy instabilities. Alternate quantizations that attempt to avoid the problem all sacrifice the classical correspondence limit which is a disaster for theories of gravitation. I also argue that efforts to legitimize local higher derivative models with ghosts are misguided because stronger...

58. From fakeons and Lee-Wick models to quantum gravity

Prof. Damiano Anselmi

22/06/2018, 09:25

A consistent theory of quantum gravity is presented. It is built as a higher derivative theory, where the would-be ghosts are tuned into "fakeons" (i.e. fake degrees of freedom) by means of a new quantization prescription. The fakeons disentangle the real parts of the amplitudes from their imaginary parts, thereby making renormalizability compatible with unitarity. The theory is essentially...

6. Classical and quantum dynamics of higher-derivative systems

Prof. Andrei Smilga

22/06/2018, 09:50

A brief review of the physics of systems including higher derivatives in the Lagrangian is given. All such systems involve ghosts, i.e. the spectrum of the Hamiltonian is not bounded from below and the vacuum ground state is absent. Usually this leads to collapse and loss of unitarity. In certain special cases, this does not happen, however: ghosts are benign.
We speculate that the Theory of...

61. Recent progress in fighting ghosts in quantum gravity

Prof. Ilya Shapiro

22/06/2018, 10:40

The main difficulty of perturbative quantum gravity (QG) in D=4 is the conflict between renormalizability and unitarity of the theory. The simplest version of QG is based on General Relativity and is non-renormalizable. One can construct renormalizable and even superrenormalizable versions of QG by introducing higher derivatives, but this leads to emergence of unphysical higher-derivative...

37. Quadratic Gravity

Dr Salvio Alberto (CERN)

22/06/2018, 11:05

Adding terms quadratic in the curvature to the Einstein-Hilbert action renders gravity renormalizable. This property is preserved in the presence of the most general renormalizable couplings with (and of) a generic quantum field theory. The price to pay is a massive ghost, which is due to the higher derivatives that the terms quadratic in the curvature imply. This quadratic gravity scenario...