DSpace Collection:
http://hdl.handle.net/2433/48879
2019-10-23T18:09:07ZMinimally Modified Gravity: a Hamiltonian Construction
http://hdl.handle.net/2433/244292
Title: Minimally Modified Gravity: a Hamiltonian Construction
Authors: Noui, Karim; Mukohyama, Shinji
Abstract: Minimally modified gravity theories are modifications of general relativity with two local gravitational degrees of freedom in four dimensions. Their construction relies on the breaking of 4D diffeomorphism invariance keeping however the symmetry under 3D diffeomorphisms. Here, we construct these theories from a Hamiltonian point of view. We start with the phase space of general relativity in the ADM formalism. Then, we find the conditions that the Hamiltonian must satisfy for the theory to propagate (up to) two gravitational degrees of freedom with the assumptions that the lapse and the shift are not dynamical, and the theory remains invariant under 3D diffeomorphisms. This construction enables us to recover the well-known "cuscuton" class of scalar-tensor theories in the unitary gauge. We also exhibit a new class of interesting theories, that we dubb f(H) theories, where the usual Hamiltonian constraint H of general relativity is replaced by f(H) where f is an arbitrary function.2019-07-01T00:00:00ZA random matrix model with non-pairwise contracted indices
http://hdl.handle.net/2433/243192
Title: A random matrix model with non-pairwise contracted indices
Authors: Lionni, Luca; Sasakura, Naoki
Abstract: We consider a random matrix model with both pairwise and non-pairwise contracted indices. The partition function of the matrix model is similar to that appearing in some replicated systems with random tensor couplings, such as the p-spin spherical model for the spin glass. We analyze the model using Feynman diagrammatic expansions, and provide an exhaustive characterization of the graphs that dominate when the dimensions of the pairwise and (or) non-pairwise contracted indices are large. We apply this to investigate the properties of the wave function of a toy model closely related to a tensor model in the Hamilton formalism, which is studied in a quantum gravity context, and obtain a result in favor of the consistency of the quantum probabilistic interpretation of this tensor model.2019-07-01T00:00:00ZHeterotic string field theory and new relations extending L ∞ algebra
http://hdl.handle.net/2433/241557
Title: Heterotic string field theory and new relations extending L ∞ algebra
Authors: Kunitomo, Hiroshi
Abstract: Based on the Wess-Zumino-Witten-like formulation, a gauge invariant action for heterotic string field theory is constructed at the sixth and eighth order of the Ramond field Ψ. A key relation is a kind of extension of the L ∞ algebra including another type of string products called the gauge products. Some general structure of a complete action is also discussed.
Description: The 32nd International Colloquium on Group Theoretical Methods in Physics (Group32): 9-13 July 2018, Prague, Czech Republic2019-04-24T00:00:00ZCosmological models with the energy density of random fluctuations and the Hubble-constant problem
http://hdl.handle.net/2433/237299
Title: Cosmological models with the energy density of random fluctuations and the Hubble-constant problem
Authors: Tomita, Kenji
Abstract: The fluctuation energy is derived from adiabatic random fluctuations due to second-order perturbation theory, and the evolutionary relation for it is expressed in the form of ρf = ρf (ρ), where ρ and ρf are the densities of ordinary dust and the fluctuation energy, respectively. The pressureless matter as a constituent of the universe at the later stage is assumed to consist of ordinary dust and the fluctuation energy. Next, cosmological models including the fluctuation energy as a kind of dark matter are derived using the above relation, and it is found that the Hubble parameter and the other model parameters in the derived models can be consistent with the recent observational values. Moreover, the perturbations of ρ and ρf are studied.2017-08-01T00:00:00Z