scholarly journals Non-Standard Hierarchies of the Runnings of the Spectral Index in Inflation

2017 ◽  
Author(s):  
Chris Longden
Keyword(s):  
Spectral Index ◽  
Field Model ◽  
Variable Speed ◽  
Speed Of Light ◽  
Microwave Background ◽  
Gravity Effects ◽  
Alternative Scenarios ◽  
Single Field ◽  
Canonical Quantum Gravity ◽  
Canonical Quantum

Recent analyses of cosmic microwave background surveys have revealed hints that there may be a non-trivial running of the running of the spectral index. If future experiments were to confirm these hints, it would prove a powerful discriminator of inflationary models, ruling out simple single field models. We discuss how isocurvature perturbations in multi-field models can be invoked to generate large runnings in a non-standard hierarchy, and find that a minimal model capable of practically realising this would be a two-field model with a non-canonical kinetic structure. We also consider alternative scenarios such as variable speed of light models and canonical quantum gravity effects and their implications for runnings of the spectral index.

scholarly journals CAN EFFECTS OF QUANTUM GRAVITY BE OBSERVED IN THE COSMIC MICROWAVE BACKGROUND?

2012 ◽  
Vol 21 (11) ◽  
pp. 1241001 ◽  
Author(s):  
CLAUS KIEFER ◽  
MANUEL KRÄMER
Keyword(s):  
Quantum Gravity ◽  
Cosmic Microwave Background ◽  
Background Radiation ◽  
Energy Scale ◽  
Microwave Background ◽  
Gravitational Effects ◽  
Small Quantum ◽  
Microwave Background Radiation ◽  
Canonical Quantum Gravity ◽  
Canonical Quantum

We investigate the question whether small quantum-gravitational effects can be observed in the anisotropy spectrum of the cosmic microwave background radiation. An observation of such an effect is needed in order to discriminate between different approaches to quantum gravity. Using canonical quantum gravity with the Wheeler–DeWitt equation, we find a suppression of power at large scales. Current observations only lead to an upper bound on the energy scale of inflation, but the framework is general enough to study other situations in which such effects might indeed be seen.

scholarly journals Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Samuele Ronchini ◽  
Gor Oganesyan ◽  
Marica Branchesi ◽  
Stefano Ascenzi ◽  
Maria Grazia Bernardini ◽  
...  
Keyword(s):  
Spectral Index ◽  
Proton Synchrotron ◽  
Relativistic Jets ◽  
Time Resolved ◽  
X Ray ◽  
Compact Binary ◽  
Internal Dissipation ◽  
Adiabatic Cooling ◽  
Alternative Scenarios ◽  
Steep Decay

Abstractγ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (1051 − 1053 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.

scholarly journals CONSTRAINTS IN QUANTUM GEOMETRODYNAMICS

2004 ◽  
Vol 19 (10) ◽  
pp. 1609-1638 ◽  
Author(s):  
ADRIAN P. GENTLE ◽  
NATHAN D. GEORGE ◽  
ARKADY KHEYFETS ◽  
WARNER A. MILLER
Keyword(s):  
Quantum Gravity ◽  
General Setting ◽  
Square Root ◽  
Dynamical Equations ◽  
Dynamic Content ◽  
Quantization Formalism ◽  
Canonical Quantum Gravity ◽  
First Time ◽  
Quantum Geometrodynamics ◽  
Canonical Quantum

We compare different treatments of the constraints in canonical quantum gravity. The standard approach on the superspace of 3-geometries treats the constraints as the sole carriers of the dynamic content of the theory, thus rendering the traditional dynamical equations obsolete. Quantization of the constraints in both the Dirac and ADM square root Hamiltonian approaches leads to the well known problems of time evolution. These problems of time are of both an interpretational and technical nature. In contrast, the geometrodynamic quantization procedure on the superspace of the true dynamical variables separates the issues of quantization from the enforcement of the constraints. The resulting theory takes into account states that are off-shell with respect to the constraints, and thus avoids the problems of time. We develop, for the first time, the geometrodynamic quantization formalism in a general setting and show that it retains all essential features previously illustrated in the context of homogeneous cosmologies.

scholarly journals REVISED CANONICAL QUANTUM GRAVITY VIA THE FRAME FIXING

2004 ◽  
Vol 13 (01) ◽  
pp. 165-186 ◽  
Author(s):  
SIMONE MERCURI ◽  
GIOVANNI MONTANI
Keyword(s):  
Quantum Dynamics ◽  
Fundamental Problem ◽  
Semiclassical Limit ◽  
Momentum Density ◽  
Hamiltonian Constraint ◽  
Additional Energy ◽  
Canonical Quantum Gravity ◽  
Quantum Geometrodynamics ◽  
Canonical Quantum ◽  
Natural Way

We present a new reformulation of the canonical quantum geometrodynamics, which allows one to overcome the fundamental problem of the frozen formalism and, therefore, to construct an appropriate Hilbert space associate to the solution of the restated dynamics. More precisely, to remove the ambiguity contained in the Wheeler–DeWitt approach, with respect to the possibility of a (3+1)-splitting when space–time is in a quantum regime, we fix the reference frame (i.e. the lapse function and the shift vector) by introducing the so-called kinematical action. As a consequence the new super-Hamiltonian constraint becomes a parabolic one and we arrive to a Schrödinger-like approach for the quantum dynamics. In the semiclassical limit our theory provides General Relativity in the presence of an additional energy–momentum density contribution coming from non-zero eigenvalues of the Hamiltonian constraints. The interpretation of these new contributions comes out in natural way that soon as it is recognized that the kinematical action can be recasted in such a way that it describes a pressureless, but, in general, non-geodesic perfect fluid.

Ritz-type variable speed of light (VSL) cosmology

2014 ◽  
Vol 27 (4) ◽  
pp. 523-536
Author(s):  
Santosh Devasia
Keyword(s):  
Variable Speed ◽  
Speed Of Light ◽  
Type Variable

Theory of a variable speed of light

2019 ◽  
Author(s):  
Alexis Pikoulas
Keyword(s):  
Variable Speed ◽  
Speed Of Light
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