cosmic controversies what is the explanation of cosmic
TRANSCRIPT
COSMIC CONTROVERSIES
Oct 6, 2019
What is the explanation of Cosmic Acceleration?
Rachel A Rosen Columbia University
KICP, UChicago
WHAT’S THE PROBLEM?WORKS GREAT! BUT…⇤
1.
2.
matter loops
phase transitions
3. other…
⇤ = ⇤0 + ⇤mat + ⇤pt + ⇤oth
requires a fine tuning
Close Cousin of the Hierarchy Problem
requires a fine tuning
BOTH THE CC AND THE HIGGS MASS ARE EXQUISITELY (I.E., POWER-LAW) SENSITIVE TO UV PHYSICS
m2H
= m20 �m2
t(. . . ) + . . .
STANDARD MODEL HIGGS MASS
Aristarchus of Samos
• Aristarchus proposed the first known heliocentric model of the solar system
• In order to explain the absence of observable parallax for the stars, postulated that they were very far away
• Contemporaries found the hierarchy in distance between nearby objects and distant stars to be untenable
geocentric solar system
HISTORICALLY MISLEADING
THE THING ABOUT NATURALNESS
(310-230 BC)
• When is a parameter natural?
• When is a theory natural?
• How do we discuss these rigorously without a measure?
MORE GENERALLY, WE USE “NATURAL” TO MEAN MANY THINGS
THE THING ABOUT NATURALNESS
WHY IS THE CC SO SMALL?
• The landscape
• Dark energy/modified gravity
• Other options?non-locality?
SOME POSSIBILITIES AND THEIR CURRENT STATUS
The Landscape
IS THE VALUE OF THE COSMOLOGICAL CONSTANT
THE RESULT OF ANTHROPICS IN A
LANDSCAPE OF OTHERWISE INHOSPITABLE VACUA?
HOW DO WE THINK ABOUT NATURALNESS IN THE AGE OF THE LHC?
“natural” solutions to the hierarchy problem
finely tuned Higgs massWE LIVE HERE
The Landscape
INHOSPITABLE
WHAT IS THE STATUS OF (META-)STABLE DE SITTER VACUA IN STRING THEORY?
KKLT (2003)
VS
|rV |V
� c (2018)
The Landscape
Dark Energy/Modified GravityWHAT MAKES A GIVEN MODEL COMPELLING?
Brans-Dicke
Scalar-Tensor
GalileonsMassive Gravity
Bigravity
Quintessence
Horndeskif(R)
Braneworlds
Ghost Condensate
Chameleons
Lorentz-Invariance?
Extra dimensions?
Massless spin-2 graviton?
Minimal coupling?
Dynamical DE?
Unimodular Gravity
Dark Energy/Modified GravityTO SOLVE OLD CC PROBLEM STILL NEED NON-LOCALITY?
What are the rules?
Other Options?
• QM instability of de Sitter
• Backreactions
• New understanding of EFTs + gravity
• Something else?
OUTLOOK
• None of the approaches mentioned here are NEW
• Need to return to consistency constraints and more “top-down” approaches
• — do we need a revolution?
ROLE OF THEORISTS IN THE ABSENCE OF NEW DATA?