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University of Waterloo

1. Ashoorioon, Amjad. Signatures of New Physics from the Primordial Universe.

Degree: 2007, University of Waterloo

URL: http://hdl.handle.net/10012/3188

During inflation quantum fluctuations of the field driving
inflation, known as inflaton, were stretched by inflationary
expansion to galactic size scales or even larger. A possible
implication of inflation – if it is correct – is that our
observable universe was once of sub-Planckian size. Thus inflation
could act as a magnifier to probe the short distance structure of
space-time. General arguments about the quantum theory of gravity
suggest that the short distance structure of space-time can be
modeled as arising from some corrections to the well-known
uncertainty relation between the position and momentum operators.
Such modifications have been predicted by more fundamental theories
such as string theory. This modified commutation relation has been
implemented at the first quantized level to the theory of
cosmological perturbations. In this thesis, we will show that the
aforementioned scenario of implementing the minimal length to the
action has an ambiguity: total time derivatives that in continuous
space-time could be neglected and do not contribute to the equations
of motion, cease to remain total time derivatives as we implement
minimal length. Such an ambiguity opens up the possibility for
trans-Planckian physics to leave an imprint on the ratio of tensor
to scalar fluctuations. In near de-Sitter space, we obtain the
explicit dependence of the tensor/scalar on the minimal length. Also
the first consistency relation is examined in a power-law
background, where it is found that despite the ambiguity that exists
in choosing the action, Planck scale physics modifies the
consistency relation considerably as it leads to large oscillations
in the scalar spectral index in the observable range of scales. In
the second part of the thesis, I demonstrate how the assumption of
existence of invariant minimal length can assist us to explain the
origin of cosmic magnetic fields. The third part of the thesis is
dedicated to the study of signatures of M-theory Cascade inflation.

Subjects/Keywords: Inflation; Trans-Planckian; M-theory; String Theory; M5-Brane; Cosmic Magnetic Fields

Record Details Similar Records

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Ashoorioon, A. (2007). Signatures of New Physics from the Primordial Universe. (Thesis). University of Waterloo. Retrieved from http://hdl.handle.net/10012/3188

Note: this citation may be lacking information needed for this citation format:

Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^{th} Edition):

Ashoorioon, Amjad. “Signatures of New Physics from the Primordial Universe.” 2007. Thesis, University of Waterloo. Accessed January 22, 2021. http://hdl.handle.net/10012/3188.

Note: this citation may be lacking information needed for this citation format:

Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^{th} Edition):

Ashoorioon, Amjad. “Signatures of New Physics from the Primordial Universe.” 2007. Web. 22 Jan 2021.

Vancouver:

Ashoorioon A. Signatures of New Physics from the Primordial Universe. [Internet] [Thesis]. University of Waterloo; 2007. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/10012/3188.

Note: this citation may be lacking information needed for this citation format:

Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Ashoorioon A. Signatures of New Physics from the Primordial Universe. [Thesis]. University of Waterloo; 2007. Available from: http://hdl.handle.net/10012/3188

Not specified: Masters Thesis or Doctoral Dissertation

2. Chatwin-Davies, Aidan. A Covariant Natural Ultraviolet Cutoff in Inflationary Cosmology.

Degree: 2013, University of Waterloo

URL: http://hdl.handle.net/10012/7759

In the field of quantum gravity, it is widely expected that some form of a minimum length scale, or ultraviolet cutoff, exists in nature. Recently, a new natural ultraviolet cutoff that is fully covariant was proposed. In the literature, most studies of ultraviolet cutoffs are concerned with Lorentz-violating ultraviolet cutoffs. The difficulty in making a minimum length cutoff covariant is rooted in the fact that any given length scale can be further Lorentz contracted. It was shown that this problem is avoided by the proposed covariant cutoff by allowing field modes with arbitrarily small wavelengths to still exist, albeit with exceedingly small, covariantly-determined bandwidths. In other words, the degrees of freedom of sub-Planckian modes in time are highly suppressed.
The effects of this covariant ultraviolet cutoff on the kinematics of a scalar quantum field are well understood. There is much to learn, however, about the effects on a field’s dynamics. These effects are of great interest, as their presence may have direct observational consequences in cosmology. As such, this covariant ultraviolet cutoff offers the tantalizing prospect of experimental access to physics at the Planck scale.
In cosmology, the energy scales that are probed by measurements of cosmic microwave background (CMB) statistics are the closest that we can get to the Planck scale. In particular, the statistics of the CMB encodes information about the quantum fluctuations of the scalar inflaton field. A measure of the strength of a field’s quantum fluctuations is in turn given by the magnitude of the field’s Feynman propagator. To this end, in this thesis I study how this covariant ultraviolet cutoff modifies the Feynman propagator of a scalar quantum field.
In this work, I first calculate the cutoff Feynman propagator for a scalar field in flat spacetime, and then I address the cutoff Feynman propagator of a scalar field in curved spacetime. My studies culminate with an explicit calculation for the case of a power-law Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime. This last calculation is cosmologically significant, as power-law FLRW spacetime is a prototypical and realistic model for early-universe inflation.
In preparation for studying the covariant cutoff on curved spacetime, I will review the necessary back- ground material as well as the kinematic influence of the covariant cutoff. I will also discuss several side results that I have obtained on scalar quantum field theories in spacetimes which possess a finite start time.

Subjects/Keywords: theoretical physics; mathematical physics; cosmology; quantum field theory; quantum gravity; Planck scale effects; trans-Planckian; UV cutoff

…covariantly-determined bandwidths. In other
words, the degrees of freedom in time of sub-*Planckian*…

Record Details Similar Records

❌

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Chatwin-Davies, A. (2013). A Covariant Natural Ultraviolet Cutoff in Inflationary Cosmology. (Thesis). University of Waterloo. Retrieved from http://hdl.handle.net/10012/7759

Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^{th} Edition):

Chatwin-Davies, Aidan. “A Covariant Natural Ultraviolet Cutoff in Inflationary Cosmology.” 2013. Thesis, University of Waterloo. Accessed January 22, 2021. http://hdl.handle.net/10012/7759.

Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^{th} Edition):

Chatwin-Davies, Aidan. “A Covariant Natural Ultraviolet Cutoff in Inflationary Cosmology.” 2013. Web. 22 Jan 2021.

Vancouver:

Chatwin-Davies A. A Covariant Natural Ultraviolet Cutoff in Inflationary Cosmology. [Internet] [Thesis]. University of Waterloo; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/10012/7759.

Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Chatwin-Davies A. A Covariant Natural Ultraviolet Cutoff in Inflationary Cosmology. [Thesis]. University of Waterloo; 2013. Available from: http://hdl.handle.net/10012/7759

Not specified: Masters Thesis or Doctoral Dissertation