Quantum Gravity and the fate of Lorentz invariance in the Standard Model

2006 ◽  
Author(s):  
Jorge Alfaro
Keyword(s):  
Standard Model ◽  
Quantum Gravity ◽  
Lorentz Invariance ◽  
The Standard Model

scholarly journals Constraints on Lorentz Invariance Violation from Optical Polarimetry of Astrophysical Objects

Symmetry ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 596 ◽  
Author(s):  
Fabian Kislat
Keyword(s):  
Standard Model ◽  
Quantum Gravity ◽  
Linear Polarization ◽  
Lorentz Invariance ◽  
Polarization Angle ◽  
Standard Model Extension ◽  
Polarization Measurements ◽  
Invariance Violation ◽  
The Standard Model ◽  
Lorentz Invariance Violation

Theories of quantum gravity suggest that Lorentz invariance, the fundamental symmetry of the Theory of Relativity, may be broken at the Planck energy scale. While any deviation from conventional Physics must be minuscule in particular at attainable energies, this hypothesis motivates ever more sensitive tests of Lorentz symmetry. In the photon sector, astrophysical observations, in particular polarization measurements, are a very powerful tool because tiny deviations from Lorentz invariance will accumulate as photons propagate over cosmological distances. The Standard-Model Extension (SME) provides a theoretical framework in the form of an effective field theory that describes low-energy effects due to a more fundamental quantum gravity theory by adding additional terms to the Standard Model Lagrangian. These terms can be ordered by the mass dimension d of the corresponding operator and lead to a wavelength, polarization, and direction dependent phase velocity of light. Lorentz invariance violation leads to an energy-dependent change of the Stokes vector as photons propagate, which manifests itself as a rotation of the polarization angle in measurements of linear polarization. In this paper, we analyze optical polarization measurements from 63 Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRBs) to search for Lorentz violating signals. We use both spectropolarimetric measurements, which directly constrain the change of linear polarization angle, as well as broadband spectrally integrated measurements. In the latter, Lorentz invariance violation manifests itself by reducing the observed net polarization fraction. Any observation of non-vanishing linear polarization thus leads to constraints on the magnitude of Lorentz violating effects. We derive the first set limits on each of the 10 individual birefringent coefficients of the minimal SME with d = 4 , with 95% confidence limits on the order of 10−34 on the dimensionless coefficients.

scholarly journals Constraints on Lorentz Invariance Violation From Optical Polarimetry of Astrophysical Objects

2018 ◽  
Author(s):  
Fabian Kislat
Keyword(s):  
Standard Model ◽  
Quantum Gravity ◽  
Gamma Ray ◽  
Lorentz Invariance ◽  
Effective Field ◽  
Energy Scale ◽  
Theory Of Relativity ◽  
Standard Model Extension ◽  
Polarization Measurements ◽  
The Standard Model

Theories of quantum gravity suggest that Lorentz invariance, the fundamental symmetry of the Theory of Relativity, may be broken at the Planck energy scale. While any deviation from conventional Physics must be minuscule in particular at attainable energies, this hypothesis motivates ever more sensitive tests of Lorentz symmetry. In the photon sector, astrophysical observations, in particular polarization measurements, are a very powerful tool because tiny deviations from Lorentz invariance will accumulate as photons propagate over cosmological distances. The Standard-Model Extension (SME) provides a theoretical framework in the form of an effective field theory that describes low-energy effects due to a more fundamental quantum gravity theory by adding additional terms to the Standard Model Lagrangian. These terms can be ordered by the mass dimension d of the corresponding operator and lead to a wavelength, polarization, and direction dependent phase velocity of light. In this paper, we analyze optical polarization measurements from 63 Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRBs) in order to search for Lorentz violating signals. We derive the first set limits on each of the 10 individual birefringent coefficients of the minimal SME with d = 4, with 95% confidence limits on the order of 10−34 on the dimensionless coefficients.

scholarly journals THE MASS OF THE NEUTRINOS

2010 ◽  
Vol 19 (11) ◽  
pp. 2285-2292
Author(s):  
B. G. SIDHARTH
Keyword(s):  
Dirac Equation ◽  
Standard Model ◽  
Special Relativity ◽  
Lorentz Invariance ◽  
The Standard Model

In the theory of the Dirac equation and in the standard model, the neutrino is massless. Both these theories use Lorentz invariance. In modern approaches however, spacetime is no longer smooth, and this modifies special relativity. We show how such a modification throws up the mass of the neutrino.

The Higgs impact on Einstein’s gravity: The Einstein–Kraichnan quantum gravity

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040012
Author(s):  
M. D. Maia ◽  
V. B. Bezerra
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Standard Model ◽  
Quantum Gravity ◽  
Higgs Mechanism ◽  
Quantum Field ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Fundamental Interactions ◽  
The Standard Model

An updated review of Kraichnan’s derivation of Einstein’s equations from quantum field theory is presented, including the period after the discovery of the Higgs mechanism and the inclusion of gravitation within the Standard Model of Fundamental Interactions.

scholarly journals Global properties of physically interesting Lorentzian spacetimes

2016 ◽  
Vol 25 (14) ◽  
pp. 1650106
Author(s):  
Deloshan Nawarajan ◽  
Matt Visser
Keyword(s):  
Standard Model ◽  
Quantum Gravity ◽  
Particle Physics ◽  
Causal Structure ◽  
Complex Structure ◽  
Good Representation ◽  
Global Features ◽  
Metric Tensor ◽  
Global Issues ◽  
The Standard Model

Under normal circumstances most members of the general relativity community focus almost exclusively on the local properties of spacetime, such as the locally Euclidean structure of the manifold and the Lorentzian signature of the metric tensor. When combined with the classical Einstein field equations this gives an extremely successful empirical model of classical gravity and classical matter — at least as long as one does not ask too many awkward questions about global issues, (such as global topology and global causal structure). We feel however that this is a tactical error — even without invoking full-fledged “quantum gravity” we know that the standard model of particle physics is also an extremely good representation of some parts of empirical reality; and we had better be able to carry over all the good features of the standard model of particle physics — at least into the realm of semi-classical quantum gravity. Doing so gives us some interesting global features that spacetime should possess: On physical grounds spacetime should be space-orientable, time-orientable, and spacetime-orientable, and it should possess a globally defined tetrad (vierbein, or in general a globally defined vielbein/[Formula: see text]-bein). So on physical grounds spacetime should be parallelizable. This strongly suggests that the metric is not the fundamental physical quantity; a very good case can be made for the tetrad being more fundamental than the metric. Furthermore, a globally-defined “almost complex structure” is almost unavoidable. Ideas along these lines have previously been mooted, but much is buried in the pre- arXiv literature and is either forgotten or inaccessible. We shall revisit these ideas taking a perspective very much based on empirical physical observation.

Sign in / Sign up

Export Citation Format

Share Document