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Related Experiment Video

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Experimental Measurement of Settling Velocity of Spherical Particles in Unconfined and Confined Surfactant-based Shear Thinning Viscoelastic Fluids

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Viscosity bound and causality violation.

Mauro Brigante¹, Hong Liu, Robert C Myers

¹Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Physical Review Letters

|June 4, 2008

Summary

This summary is machine-generated.

This study demonstrates that conformal field theories (CFTs) with Gauss-Bonnet gravity duals violating the viscosity bound lead to microcausality violations. This suggests a universal lower bound on the shear viscosity to entropy density ratio for consistent theories.

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Area of Science:

Theoretical Physics
Quantum Field Theory
String Theory

Background:

Recent work indicated that certain conformal field theories (CFTs) with Gauss-Bonnet gravity duals could violate the conjectured viscosity bound (eta/s > or = 1/4 pi).
The shear viscosity to entropy density ratio (eta/s) is a crucial transport coefficient in understanding the properties of quantum fluids.

Purpose of the Study:

To investigate the implications of violating the conjectured viscosity bound in CFTs with Gauss-Bonnet gravity duals.
To explore the relationship between microcausality, theory consistency, and the lower bound on the shear viscosity to entropy density ratio.

Main Methods:

Analysis of a specific class of conformal field theories (CFTs) featuring Gauss-Bonnet gravity duals.
Investigating the consequences of tuning the shear viscosity to entropy density ratio (eta/s) below a critical value.

Main Results:

Tuning eta/s below (16/25)(1/4 pi) in the studied CFT model induces microcausality violation.
This violation renders the conformal field theory inconsistent, demonstrating a direct link between viscosity bounds and theoretical consistency.

Conclusions:

The findings provide a concrete example correlating theory inconsistency with a lower bound on viscosity.
This supports the hypothesis of a potential universal lower bound on eta/s for all physically consistent theories.