The Experts below are selected from a list of 4575 Experts worldwide ranked by ideXlab platform

Antonin Coutant - One of the best experts on this subject based on the ideXlab platform.

  • Semiclassical Momentum representation in quantum cosmology
    Physical Review D, 2016
    Co-Authors: Antonin Coutant
    Abstract:

    It is well-known that the standard WKB approximation fails to provide semiclassical solutions in the vicinity of turning points. However, turning points arise in many cosmological scenarios. In a previous work, we obtained a new class of semiclassical solutions of the Wheeler-deWitt equation using the Conjugate Momentum to the geometric variable. We present here a detailed study of their main properties. We carefully compare them to usual WKB solutions and turning point resolutions using Airy functions. We show that the Momentum representation possesses many advantages that are absent in other apporaches. In particular, this framework has a key application in tackling the problem of time. It allows us to use curvature as a time variable, and control the corresponding domain of validity, i.e. under which conditions it provides a good clock. We consider several applications, and in particular show how this allows us to obtain semiclassical solutions of the Wheeler-DeWitt equation parametrized by York time.

  • Unitary and non-unitary transitions around a cosmological bounce
    Physical Review D, 2014
    Co-Authors: Antonin Coutant
    Abstract:

    In this work, we investigate the notion of time and unitarity in the vicinity of a bounce in quantum cosmology, that is, a turning point for the scale factor. Because WKB methods drastically fail near a turning point, the scale factor cannot play the role of time in such scenarios. We overcome this diculty by studying the dynamics of matter transitions when using its Conjugate Momentum as a time. We nd precise conditions so as to recover unitarity, and hence, a consistent notion of probability. We then compute transitions in a concrete example, extract the specic feature of a bounce and argue about the necessity of the Conjugate Momentum representation to go beyond the background eld approximation. Our analysis is also equally relevant

David Kaiser - One of the best experts on this subject based on the ideXlab platform.

  • relativistic corrections to nonrelativistic effective field theories
    Physical Review D, 2018
    Co-Authors: Mohammad Hossein Namjoo, Alan H Guth, David Kaiser
    Abstract:

    In this paper we develop a formalism for studying the nonrelativistic limit of relativistic field theories in a systematic way. By introducing a simple, nonlocal field redefinition, we transform a given relativistic theory, describing a real, self-interacting scalar field, into an equivalent theory, describing a complex scalar field that encodes at each time both the original field and its Conjugate Momentum. Our low-energy effective theory incorporates relativistic corrections to the kinetic energy as well as the backreaction of fast-oscillating terms on the behavior of the dominant, slowly varying component of the field. Possible applications of our new approach include axion dark matter, though the methods developed here should be applicable to the low-energy limits of other field theories as well.

Giovanni Montani - One of the best experts on this subject based on the ideXlab platform.

  • Polymer quantum dynamics of the Taub universe
    Physical Review D, 2008
    Co-Authors: Marco Valerio Battisti, Orchidea Maria Lecian, Giovanni Montani
    Abstract:

    Within the framework of nonstandard (Weyl) representations of the canonical commutation relations, we investigate the polymer quantization of the Taub cosmological model. The Taub model is analyzed within the Arnowitt-Deser-Misner reduction of its dynamics, by which a time variable arises. While the energy variable and its Conjugate Momentum are treated as ordinary Heisenberg operators, the anisotropy variable and its Conjugate Momentum are represented by the polymer technique. The model is analyzed at both classical and quantum level. As a result, classical trajectories flatten with respect to the potential wall, and the cosmological singularity is not probabilistically removed. In fact, the dynamics of the wave packets is characterized by an interference phenomenon, which, however, is not able to stop the evolution towards the classical singularity.

Arup Barua Apu - One of the best experts on this subject based on the ideXlab platform.

  • Noncommutative scalar fields in compact spaces: quantisation and implications
    Progress of Theoretical and Experimental Physics, 2017
    Co-Authors: Mir Mehedi Faruk, Mishkat Al Alvi, Wasif Ahmed, Muktadir Rahman, Arup Barua Apu
    Abstract:

    In this paper we consider a two component scalar field theory, with noncommutativity in its Conjugate Momentum space. We quantize such a theory in a compact space with the help of dressing transformations and we reveal a significant effect of introducing such noncommutativity as the splitting of the energy levels of each individual mode that constitutes the whole system. We further compute the thermal partition function exactly with predicted deformed dispersion relations from noncommutative theories and compare the results with usual results. It is found that thermodynamic quantities in noncommutative models, irrespective of whether the model is more deformed in infrared/UV region, show deviation from standard results in high temperature region.

Stanislaw Mrowczynski - One of the best experts on this subject based on the ideXlab platform.

  • Wigner functional of fermionic fields
    Physical Review D, 2013
    Co-Authors: Stanislaw Mrowczynski
    Abstract:

    The Wigner function, which provides a phase-space description of quantum systems, has various applications in quantum mechanics, quantum kinetic theory, quantum optics, radiation transport and others. The concept of Wigner function has been extended to quantum fields, scalar and electromagnetic. Then, one deals with the Wigner functional which gives a distribution of field and its Conjugate Momentum. We introduce here the Wigner functional of fermionic fields of the values in a Grassmann algebra. Properties of the functional are discussed and its equation of motion, which is of the Liouville's form, is derived.