Superluminality in Effective Field Theories for Cosmology

Conference Date: 
Thursday, April 9, 2015 (All day) to Saturday, April 11, 2015 (All day)
Scientific Areas: 
Cosmology

 

Some effective field theories popular in cosmology exhibit superluminality; they contain fluctuations that propagate faster than the speed of light around non-trivial backgrounds. There is controversy as to whether this kind of superluminality is actually a trustable physical feature of the effective theory, or merely an artifact of using an incomplete effective theory or of asking the wrong questions.  Even if it is trustable, there is controversy as to whether this spells trouble for a theory, i.e. ruling out a UV completion, or whether it is harmless.  This workshop will aim to bring people on all sides to Perimeter, with the goal of making progress on these issues.

Sponsorship for this workshop has been provided by:

  • Lasha Berezhiani, University of Pennsylvania
  • Paolo Creminelli, International Centre for Theoretical Physics
  • Cedric Deffayet, Laboratoire Astroparticule et Cosmologie (APC)
  • Sergei Dubovsky, New York University
  • Gregory Gabadadze, New York University
  • Fawad Hassan, Stockholm University
  • Timothy Hollowood, Swansea University
  • Keisuke Izumi, National Taiwan University
  • Alberto Nicolis, Columbia University
  • Antonio Padilla, University of Nothingham
  • Massimo Porrati, New York University
  • Raquel Ribeiro, Queen Mary University of London
  • Andrew Tolley, Case Western Reserve University
  • Alex Vikman, Ludwig-Maximillian University 
  • Andrew Waldron, University of California, Davis
  • George ZahariadeUniversity of California, Davis
  • Lasha Berezhiani, University of Pennsylvania
  • Alejandro Cardenas AvendanoUniversidad Nacional de Colombia
  • Paolo Creminelli, International Centre for Theoretical Physics
  • Cedric Deffayet, Laboratoire Astroparticule et Cosmologie (APC)
  • Sergei Dubovsky, New York University
  • Matteo Fasiello, Stanford University
  • Antonia Frassino, Perimeter Institute
  • Gregory Gabadadze, New York University
  • Mariana Gonzalez, Perimeter Institute
  • Garret Goon, Cambridge University
  • Fawad Hassan, Stockholm University
  • Kurt Hinterbichler, Perimeter Institute
  • Timothy Hollowood, Swansea University
  • Lam Hui, Columbia University
  • Keisuke Izumi, National Taiwan University
  • Austin Joyce, University of Chicago
  • Justin Khoury, University of Pennsylvania
  • Andrew Matas, Case Western Reserve University
  • John Moffat, Perimeter Institute
  • Antonio Padilla, University of Nothingham
  • Riccardo Penco, Columbia University
  • Massimo Porrati, New York University
  • Raquel Ribeiro, Queen Mary University of London
  • Rachel Rosen, Columbia University
  • Alexandra Terrana, Perimeter Institute
  • Andrew Tolley, Case Western Reserve University
  • Mark Trodden, University of Pennsylvania
  • Alex Vikman, Ludwig-Maximillian University 
  • Andrew Waldron, University of California, Davis
  • George ZahariadeUniversity of California, Davis

Thursday, April 9, 2015

Time

Event

Location

8:30 – 9:00am

Registration

Reception

9:00 – 9:15am

Welcome and Opening Remarks

Bob Room

9:15 – 9:45am

George Zahariade, University of California, Davis
TBA

Bob Room

9:45 – 10:30am

Keisuke Izumi, National Taiwan University
Causal structures in Massive gravity and Gauss-Bonnet gravity

Bob Room

10:30 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 12:30pm

Andrew Tolley, Case Western Reserve University
Superluminalities in Galileon theories

Bob Room

12:30 – 2:30pm

Lunch

Bistro – 2nd Floor

2:30 – 3:15pm

Gregory Gabadadze, New York University
TBA

Bob Room

3:15 – 3:45pm

Lasha Berezhiani, University of Pennsylvania
Subluminal Vainshtein Screening in Massive Gravity

Bob Room

3:45 – 4:30pm

Coffee Break

Bistro – 1st Floor

4:30 – 5:30pm

Andrew Tolley, Case Western Reserve University
Superluminalities in Galileon theories

Bob Room

Friday, April 10, 2015

Time

Event

Location

9:00 – 9:45am

Timothy Hollowood, Swansea University
Causality constraints and the lightcone

Bob Room

9:45 – 10:30am

Sergei Dubovsky, New York University
Asymptotic fragility, superluminality and pi

Bob Room

10:30 – 11:00am

Coffee Break

Bistro – 1st Floor

11:00 – 11:45am

Alex Vikman, Ludwig-Maximillian University
TBA 

Bob Room

11:45 – 12:30pm

Massimo Porrati, New York University
Multi-Field Born-Infeld Lagrangians, Nilpotent Fields, N=2 
Supersymmetry and Cubic Polynomials

Bob Room

12:30 – 2:30pm

Lunch Break

Bistro – 2nd Floor

2:30 – 3:15pm

Cedric Deffayet, Laboratoire Astroparticule et Cosmologie
Galileon p-forms

Bob Room

3:15 – 4:00pm

Antonio Padilla, University of Notthingham
The Cosmological Constant Problem (and its sequester)

Bob Room

4:00 – 4:15pm

Conference Photo   

TBA

4:15 – 4:45pm

Coffee Break

Bistro – 1st Floor

4:45 – 5:30pm

Alberto Nicolis, Columbia University
TBA

Bob Room

6:00pm Onwards

Banquet

Bistro – 2nd Floor

Saturday, April 11, 2015

Time

Event

Location

9:00 – 9:45am

Raquel Ribeiro, Queen Mary University of London
Lessons from QuantumLand

Bob Room

9:45 – 10:30am

Paolo Creminelli, International Centre for Theoretical Physics
Galileon dualities and superluminality

Bob Room

10:30 – 11:00am

Coffee Break

Bistro – 1st floor

11:00 – 11:30am

Fawad Hassan, Stockholm University
Some recent results in Bimetric Theory

Bob Room

11:30 – 12:15pm

Andrew Waldron, University of California, Davis
Quantum Gravity and Causal Structures

Bob Room

12:15pm

Lunch

Bistro – 1st floor

 

Lasha Berezhiani, University of Pennsylvania

Subluminal Vainshtein Screening in Massive Gravity

I will discuss the Vainshtein mechanism in massive gravity. I will show that the spherically symmetric backgrounds that were believed to have superluminal sound speed are in fact unstable. Instead, there is a new class of phenomenologically relevant solutions with stable and subluminal perturbations.

Paolo Creminelli, International Centre for Theoretical Physics

Galileon dualities and superluminality

Cedric Deffayet, Laboratoire Astroparticule et Cosmologie (APC)

Galileon p-forms

I will discuss generalizations and no-go theorems for generalizations to p-forms of Galileon actions

Sergei Dubovsky, New York University

Asymptotic fragility, superluminality and pi

Fawad Hassan, Stockholm University

Some recent results in Bimetric Theory

This talk will summarize some recent results in bimetric theory, including the existence of the square-root matrix, possible connection to partial masslessness and conformal gravity, the structure of constraints and finally, the cosmological implications of the theory.

Timothy Hollowood, Swansea University

 Causality constraints and the lightcone

It is an attractive idea that effective theories admitting a consistent UV completion require quanta to propagate sub-luminally in non-trivial backgrounds.  However, there is a counter example to this proposition in the form of QED in a curved geometry, a theory that is certainly causal. Nevertheless, Drummond and Hathrell showed that there is always at least one choice of polarization for which low frequency photons propagate super-luminally. Conventional arguments involving dispersion relations would then normally imply that the high frequency phase velocity would also exceed c yielding a contradiction with the UV completion. We show how the contradiction is avoided by a mechanism that relies on the subtle behaviour of the lightcones in the geometry and that, in the end, super-luminal low frequency propagation is perfectly consistent with causality. In particular, time machines cannot be constructed using the effect. The lesson is that causality constraints in low energy effective theories need to be treated with some caution.

Keisuke Izumi, National Taiwan University

Causal structures in Massive gravity and Gauss-Bonnet gravity

In General Relativity, gravitons propagate to null directions, because of its well-organized structures. Modifying the gravity theory slightly, meanwhile, the beautiful structure is broken and gravitons can easily propagate superluminaly. Here, applying the characteristic method, which is the well-established powerful way to analyze causal structures, the causal structures in Massive gravity and Gauss-Bonnet gravity are analyzed. We discuss the superluminality, acausality and black holes. 

Antonio Padilla, University of Nottingham

The Cosmological Constant Problem (and its sequester)

I will review the notorious cosmological constant problem, sometimes described as the worst fine tuning problem in Physics. I will explain the true nature of the problem, which is one of radiative instability against any change in the effective description. I will recall Weinberg’s venerable no-go theorem that prohibits certain attempts to “solve” this problem before going on to explain a new mechanism that circumvents Weinberg. This is the vacuum energy sequester, a global modification of GR that results in the cancellation of large vacuum energy contributions from a protected matter sector (taken to include the Standard Model) at each and every order in the perturbative loop expansion. Cosmological consequences are a Universe which has finite space-time volume, will ultimately crunch, and for which dark energy can only be a transient. Furthermore, using a linear scalar potential within the sequestering set-up, I will show that dark energy today can be intimately related to the trigger that brings about cosmological collapse in the not too distant future, at the same time providing a possible solution to the “Why Now?” problem.

Massimo Porrati, New York University

Multi-Field Born-Infeld Lagrangians, Nilpotent Fields, N=2 
Supersymmetry and Cubic Polynomials
 
We show how nonlinearly realized N=2 supersymmetry gives rise, in the low-energy limit, to an N=1 Born-Infeld U(1) Lagrangian. We then extend the construction to many N=2 vector multiplets. We show how the classification of inequivalent nilpotency constraints arising in the low-energy limit is connected  to the theory of cubic polynomials and curves. We comment on causality of signal propagation in these systems.
 
Raquel Ribeiro, Queen Mary University of London
 
Lessons from QuantumLand
 
Theories with large kinetic interactions have very relevant phenomenological applications in cosmology, in particular in the context of cosmic acceleration. Their Effective Field Theory (EFT) description relies on the so-called Vainshtein effect being operative. When incorporated at the quantum level, this mechanism ensures the validity of the theory in a non-trivial way. I will discuss how to estimate the regime of validity of such EFTs on the basis of computing the quantum corrections to the classical theory. I will point out how some lessons learned from the study of quantum effects in these theories might help us to tackle the significance of superluminalities and revisit what properties a healthy EFT should have.
 
Andrew Tolley, Case Western Reserve University
 
Superluminalities in Galileon theories
 
Andrew Waldron, University of California, Davis
 
Quantum Gravity and Causal Structures

 

 

 

Saturday Apr 11, 2015
Speaker(s): 

This talk will summarize some recent results in bimetric theory, including the existence of the square-root matrix, possible connection to partial masslessness and conformal gravity, the structure of constraints and finally, the cosmological implications of the theory.

Scientific Areas: 
 

 

Saturday Apr 11, 2015
Speaker(s): 

Theories with large kinetic interactions have very relevant phenomenological applications in cosmology, in particular in the context of cosmic acceleration. Their Effective Field Theory (EFT) description relies on the so-called Vainshtein effect being operative. When incorporated at the quantum level, this mechanism ensures the validity of the theory in a non-trivial way. I will discuss how to estimate the regime of validity of such EFTs on the basis of computing the quantum corrections to the classical theory.

Scientific Areas: 
 

 

Friday Apr 10, 2015
Speaker(s): 
 

 

Friday Apr 10, 2015
Speaker(s): 

I will review the notorious cosmological constant problem, sometimes described as the worst fine tuning problem in Physics. I will explain the true nature of the problem, which is one of radiative instability against any change in the effective description. I will recall Weinberg’s venerable no-go theorem that prohibits certain attempts to “solve” this problem before going on to explain a new mechanism that circumvents Weinberg.

Scientific Areas: 
 

 

Friday Apr 10, 2015
Speaker(s): 

I will discuss generalizations and no-go theorems for generalizations to p-forms of Galileon actions

Scientific Areas: 
 

 

Friday Apr 10, 2015
Speaker(s): 

We show how nonlinearly realized N=2 supersymmetry gives rise, in the low-energy limit, to an N=1 Born-Infeld U(1) Lagrangian. We then extend the construction to many N=2 vector multiplets. We show how the classification of inequivalent nilpotency constraints arising in the low-energy limit is connected to the theory of cubic polynomials and curves. We comment on causality of signal propagation in these systems.

Scientific Areas: 

Pages

Scientific Organizers:

Kurt Hinterbichler, Perimeter Institute
Rachel Rosen, Columbia University