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IGC Inaugural ConferencePenn. State University
8/9/2007
Mark TroddenSyracuse University?CosmologyThe Road Ahead
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Outline
• Introduction.• The Universe Observed, Circa 2007• The Mysteries of the Pie Chart• What might our observations be revealing about fundamental physics? - Connections to particle physics
- The importance of gravity
- Some examples and constraints• Summary
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Establishing the New Cosmology
10 100 500 10000
1000
2000
3000
4000
5000
600090° 2° 0.5° 0.2°
?
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Three Problems
• Three problems posed by observational cosmology - a great achievement, but raises many issues.
• Need fundamental physics to understand what the universe is made of and why these observations look the way they do.
• It seems inevitable that this will require new particles and new symmetries.
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
• Originally noticed through galaxy rotation curves • One modern way to look for it - weak gravitational lensing
Dark Matter
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
How to Use itCan reconstruct thedensity in the cluster
What is this stuff?
• WIMPs?• SUSY particles?• Axions? • Remnants of GUTs?• …
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Seems to Really be Particles!
Hubble
Chandra
HST, Chandra + Lensing
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
BSM Physics & Dark Matter
There is a very broad connection between models of beyondthe standard model physics (particularly those addressing
the hierarchy problem) and dark matter• Almost any model involves new particles at the TeV scale, related to the SM particles through new symmetries (SUSY partners, KK partners, extra gauge and scalar partners, ...)• Typically, to avoid things like proton decay and precision EW tests, an extra new symmetry is required (R-parity, KK-parity, T-parity, ...).• This new symmetry renders stable some new particle at the weak scale
Often, this stable new particle is an ideal WIMP candidate!
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Dark Matter• A prime dark matter candidate is the WIMP - a new stable particle. • Number density n determined by
Dilution fromexpansion
dndt
= −3Hn − σv n2 − neq2( )
Exponentialdrop
Freeze out
Annihilations
• Initially, term dominates, so n ≈ neq.
• Eventually, n becomes so small that dilution term dominates
• Co-moving number density is fixed (freeze out).
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Abundance of WIMPs• Weakly-interacting particles
w/ weak-scale masses give ΩDM • Strong, fundamental, and
independent motivation for new physics at weak scale
Universe cools, leaves residue of dark matter
with ΩDM ~ 0.1 (σWeak/σ)• Could use the colliders as a dark matter laboratory• Discover WIMPs and determine their properties• Consistency between properties (particle physics) and abundance (cosmology) may lead to understanding of Universe at T = 10 GeV, t = 10-8 s.Can compare this program with the one that led (withspectacular success) to our understanding of BBN via
adetailed understanding of nuclear physics
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Dark MatterIn this case, the DM candidate is the LSP - here’s what we’d love to do (I’ve cheated slightly)
WMAP(current)
Planck(~2010)
LHC (“best case scenario”)
[Thanks to J. Feng]
ILC
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Another Fundamental Problem
•Essentially, observable universe, out to the Hubble size, is made of matter and not antimatter
•Can construct a ladder of evidence
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Baryogenesis
BBN and CMB have determined
the cosmic baryon content:
ΩBh2 = 0.024 ± 0.001
To achieve this a particle theoryrequires (Sakharov, 1968) :
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
A Connection to TeV Physics• However, an attractive and testable possibility is that
the asymmetry is generated at the weak scale.
• The Standard Model of particle physics, satisfies all 3 Sakharov criteria in principle, (anomaly, CKM matrix, finite-temperature phase transition)
• Exciting, but turns out not enough CPV and a continuous EWPT. Therefore, cannot be sufficient to explain the baryon asymmetry!
• This is a clear indication, from observations of the universe, of physics beyond the standard model - new particles and new symmetries!
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Cosmic Acceleration
Not only is the universe expanding:But it is accelerating!
ȧ≡ dadt
> 0
ä≡ ddtȧ> 0
- new particles and new symmetries!
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Logical Possibilities for Acceleration
Gµν = 8πGTµνNew Mass/Energy
SourcesModifications of
Gravity
QuintessenceK-essence
Oscillating DE...
Inverse Curvature Gravity
DGP BraneworldsCardassian Models
...
Cosmological ConstantExtra Dimensions
BackreactionEnvironmental Selection
...
Other
[Carroll, Duvvuri, Trodden, Turner; Dvali, Gabadadze, Porrati; Freese, Lewis; De Felice, Easson; Flanagan; ...] [Kolb, Matarrese, Notari,
Riotto; Brandenberger; Abramo, Woodard; Weinberg; Vilenkin; Linde; Bousso, Polchinski; ...]
[Ratra, Peebles; Wetterich; Caldwell, Dave, Steinhardt; Freiman, Hill, Stebbins, Waga; Armendariz-Picon, Mukhanov; Bean; ... ......... Basically every cosmologist you can think of ... and most particle theorists as well.]
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Dark Energy - Theory
Evolution of the universe governed by Einstein eqns
The Friedmann equation
The “acceleration” equation
Parameterize different types of matter by equations of state: pi=wiρi
When evolution dominated by type i, obtain
(wi ≠ -1)
H2 ≡(ȧa
)2∝ ρ
a(t) ∝ t2/3(1+wi) ρ(a) ∝ a−3(1+wi)
äa∝−(ρ+3p)
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Cosmic Acceleration
So, accelerating expansion means
p
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
A Cosmological Constant or Not?
“If it bleeds, we can kill it”Arnold Schwarzenegger as Dutch Schaeffer, Predator (1987)
What the Governator is trying to tell us is that our best chance of testing the origin of acceleration is if it is not a cosmological constant
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Data on w
We’ll come back laterto discuss what is really
being measured here
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
The Cosmological Constant• A long-standing problem for fundamental theory.• Has a clear connection to particle physics• Vacuum is full of virtual particles carrying energy. • Should lead to a constant vacuum energy. How big? -
• While calculating branching ratios - easy to forget SUSY is a space-time symmetry.
Still 1060 too big!
BUT
∞
At this stage, fair to say we are stuck! Help needed!
ρΛ ∼M4SUSYe-
γe+
γ
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Quintessence - Dark EnergyMaybe there’s some principle that sets vacuum energy to zero. Then dark energy might be like low-scale inflation today.
V(φ)
φ
Difference: no minimum or reheating
Use scalar fields to source Einstein’s equation.
Homogeneity gives
Small slope
ρφ =12φ̇2+
12(∇φ)2+V (φ)
φ̈+3Hφ̇+dVdφ
= 0
ρφ ≈V (φ)≈ constant w=−[2V (φ)− φ̇2
2V (φ)+ φ̇2
]
L=12
(∂µφ)∂µφ−V (φ)
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Are we Being Fooled by Gravity?
We don’t really measure w - we infer it from the Hubble plot via
Maybe, if gravity is modified, can infer value not directlyrelated to energy sources (or perhaps without them!)
we f f =−1
1−Ωm
(1+
23ḢH2
)
One example - Brans-Dicke theories
ω>40000 (Signal timing measurements from Cassini) We showed that (with difficulty) can measure w
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
In Fact, Maybe it’s All Gravity!
“[General Relativity] explains ... quantitatively... the secular rotation of the orbit of Mercury,discovered by Le Verrier, ... without the needof any special hypothesis.”, SPAW, Nov 18, 1915
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
How Might We Modify Gravity?Write an Lagrangian - a scalar involving the object and its derivatives. What might this look like?
gµν
What are the propagating degrees of freedom? A first step is to identify the degrees of freedom in gµν
Answer: turns out there are scalar and vectors as well as hµν
How come we don’t see all these in GR? - Depends on the action!
The equations of motion arising from the Einstein-Hilbert action yieldconstraints, which make everything except non-dynamical!hµν
Almost any other action will free up some of the other degrees of freedom. These can yield new problems.
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Issues with new d.o.f.
A couple of different problems can arise with these new degrees of freedom.
First: Geodesics within the solar system can be appreciably altered
Second: They can lead to instabilities because they are ghost-like (have the wrong sign kinetic terms.
Best tests are from timing delays of signals fromdistant spacecraft.Particularly the Cassini mission.
These would lead, among other things, to the decayof the vacuum on a microscopic timescale
(Carroll, Hoffman & M.T., Phys.Rev. D68: 023509 (2003) [astro-ph/0301273])
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
Cosmologists admitting they want to work on the cosmology of the earliest times in the universe elicits interesting responses from:
Cosmologists : “Why work on this when there’s so much data to analyze?”QG Theorists : “What do cosmologists know about quantum gravity?”Experimentalists : “Is this physics?”
But we do need to put real effort into this because:
Particle cosmologists need to “tool up” for the new issues being raised in cosmology.The data and its rate of acquisition is breathtaking. During next 5-10 years we’ll know unprecedentedly precise facts about the universe. But what will they mean?? It is not enough just to parameterize the universe.Only through combined efforts will it become clear that this is physics.
What about Earlier Epochs?
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
• How did the observable universe become so flat and homogeneous on large scales?
• What made galaxies form (metric perturbations)?
• Why do we observe 3 spatial dimensions (and for that matter, 1 temporal one)?
• Can cosmological observations teach us anything about fundamental physics?
• Is the universe eternal or finite in time; How, if at all, did it begin?
More generally, how did fundamental physics set thevalues of the required input parameters to the
wildly successful standard cosmology?
Where’s the Action At?
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Mark Trodden, Syracuse UniversityCosmology - The Road Ahead
IGC Inaugural ConferencePenn. State University, 8/9/2007
The Road Ahead
… and many, many more…
CDMS
Thank You!