III - The Universe at large
Pierre Binétruy APC, Paris
CERN Summer Student Lecture Programme 2012 Outline
1. Detection of dark matter
2. Looking for standard candles to study dark energy
3. Towards the big bang… 1. Detcton of dark mater
Coma cluster
Studying the velocity distribution of Galaxies in the Coma cluster and using the virial theorem
2
100 kpc Vera Rubin, 1975
What is dark matter?
Not luminous matter
Not neutrinos because their random motions (free streaming) would wash out any density fluctuations and prevent the formation of galaxies (hot dark matter)
We need cold dark matter (i.e. particles with smaller free streaming length), most probably in the form of weakly interacting massive particles or wimps. χχ χ χ χ χ χ
χ
Annihilation in the heart of the Sun Detection in underground labs or at the centre of our Galaxy Direct detection χ χ
Underground labs (mines, tunnels…) arXiv:1207.5988 Annual modulation
At LHC, these particles are stable and leave the detector Unseen while taking away some of the energy :
Signature : missing energy wimp χ
Simulated event in CMS detector If one discovers at LHC one or several weakly interacting massive stable particles, will this be dark matter?
Not necessarily :
• numerous tests to make to identify their properties: mass, coupling to other particles
• necessary to show that these particles exist in our environment • indirect detection (wimps accumulate at the centre of the Sun or of the galaxy where they annihilate into energetic neutrinos, χ gammas, electrons or positrons)
ICECUBE (S. Pole)
ν
Fermi ν γ ANTARES (Toulon) HESS telescope (Namibia) γ
Launch in 2008
γ from 10 keV to 300 GeV
Large Area Telescope (20 to 300 MeV)
γ
Measuring trajectories using Si and tungsten
Measuring energies with a calorimeter Rejecting charged cosmic rays through anticoincidence A few surprises! From PAMELA which detects antiprotons and positrons
antiproton flux
No excess in antiprotons
Excess in positrons
If it is dark matter, it is non-standard because it couples preferentially to leptons.
Astrophysical source? arXiv: 0905.0025 [astro-ph]
Detecting the primary particles responsible for cosmic rays: AMS on the ISS
(launch 16 May 2011)
permanent magnet (charged particles) AMS02 anchored on the ISS
20 GeV electron 42 GeV carbon
First events collected on 19 May 2011 2. Looking for standard candles Supernovae of type Ia may be used as standard candles to test the geometry of spacetime Distant supernovae appear less bright than in an expanding universe accelerated expansion
mB = 5 log(H0dL) + M - 5 log H0 + 25
1-q0 luminosity distance d = l z ( 1 + ------z + …) L H0 2
q0 deceleration parameter Why do supernova explosion of type Ia provide standard candles?
Origin: white dwarf where gravitational force is counterbalanced by electron degeneracy pressure (hence independent of the details of the chemical composition)
The star is completely disrupted and all the energy of the explosion goes into the expansion of the products.
But the luminosity depends on the amount of Ni synthesized; for instance, less Ni means lower luminosity, but also lower temperature in the gas and thus less opacity and more rapid energy escape: dimmer supernovae are quicker.
Gamma ray bursts
Determine the luminosity through a relation between the collimation
corrected energy Eγ and the peak energy Coalescence of supermassive black holes
3. Towards te big bang Electromagnetic wave Photon
Gravitational wave Graviton If gravitons were in thermal equilibrium in the primordial universe
density
γ
g When do gravitons decouple?
5 2 Interaction rate 2 5 T GN=1/MPl Γ~ GN T ~ ----4 MPl 2 Expansion rate H ~ T---- (radiation dominated era) MPl
T3 ----Γ ~ ---- H 3 MPl
Gravitons decouple at the Planck era : fossile radiation Gravitons of frequency f* produced at temperature T* provide a background observed at a redshifted frequency
1/6 1 T g f = 1.65 10-7 Hz ------* ----* ε ( 1GeV ) ( 100 )
-1 At production λ* = ε H* (or f* = H*/ ε)
Wavelength Horizon length Gravitons of frequency f* produced at temperature T* provide a background observed at a redshifted frequency
1/6 1 T g f = 1.65 10-7 Hz ------* ----* ε ( 1GeV ) ( 100 )
-1 At production λ* = ε H* (or f* = H*/ ε)
Wavelength Horizon length T g 1/6 f = 1.65 10-7 Hz ---1 ( -----* ) ( ----* ) ε 1GeV 100
for ε=1
ΩGW ~ρGW/ρc T g 1/6 The electroweak phase transition f = 1.65 10-7 Hz ---1 ( -----* ) ( ----* ) ε 1GeV 100
for ε=1
ΩGW
Gravitons produced at the electroweak phase transition would be observed in the LISA window. But are gravitons produced in sufficient numbers at the electroweak phase transition?
If the transition is first order, nucleation of true vacuum bubbles inside the false vacuum
Collision of bubbles and turbulence → production of gravitational waves Pros and cons for a 1st order phase transition at the Terascale:
• in the Standard Model, requires mh < 72 GeV (ruled out) • MSSM requires too light a stop but generic in NMSSM • possible to recover a strong 1st order transition by including H6 terms in SM potential • other symmetries than SU(2)xU(1) at the Terascale (→ baryogenesis)
Even closer to the big bang:
Planck era where gravity is quantized
What is a quantum spacetime?
Maybe as different from our notion of a continuous spacetime as a solid piece of wood from an assemblage of atoms!
Notion of emergent spacetime → notion of emergent spacetime symmetries such as Lorentz symmetry
Expect violations of Lorentz symmetries (probe: distant sources of light such a gamma ray bursts) Conclusion
A new window is being opened towards the Universe using the knowledge accumulated over more than 50 years of high energy physics.
Back to where the field started, but this time not to understand the infinitely small, but to grasp the infinitely large.