DARK ENERGY

1
DARK ENERGY

• Lluís Galbany
• Cosmologia - Gravitació i astropartícules

2

• Introduction
• Equations
• Candidates

3

• DE -gt Modern unknown
• Universe expanding
• Observational evidence from supernovae for an
  accelerating universe and a cosmological constant
  (A.Riess et al.) 1998
• Measurements of omega and lambda from 42 high
  redshift supernovae. (S. Perlmutter et al.) 1999
• DE expansion

4
Beginnings

• Einstein wants a static universe.
• GR dont permit it (Matter attracts
  gravitionally)
• He added a term (cosmological constant) to
  arrange a static UNI
• Hubble law -gt expansion -gt problem!

5
The standard cosmological model

• Cosmological principle Universe is isotropic and
  homogeneous (on large scales)
• Metrics equation which gives the distance
  between two points
• SR -gt Minkowsky metric
• GR -gt Robertson-Walker metric
• t cosmic time
• r comoving coordinates
• a scale factor -gt expansion or
  contraction

6
Dynamics relations between curvature content
( a(t), k, R0, e(t) P(t) )

• Friedmann equation. Rel. between a(t), k, e(t)
  R0
• Fluid equation. Rel. between a(t), e(t) P(t)
• Acceleration equation. Rel. between a(t), e(t)
  P(t)
• Equation of state. Rel. between e(t) P(t)

DARK ENERGY W lt -1/3
? W -1
where w lt 1
7
Equations with lambda

• Friedmann equation. Rel. between a(t), k, e(t)
  R0
• Fluid equation. Rel. between a(t), e(t) P(t)
• Acceleration equation. Rel. between a(t), e(t)
  P(t)

Einstein wanted to find H0. In a flat Universe
8
New component

• ? fluid
• ? has a negative effective pressure.
• As UNI expands, work is done on ? fluid.
• -gt E? remains constant

-gt Energy of the empty space (vacuum)
9

• Classical physics
• (Nothing can come from nothing. King Lear)
• Quantum physics

Theory and observations dont match
10
Evidences

• Observation of SNIa
• Standarized standard candles
• The best model is OM0.3
• O?0.7

11

• Universe only with ? (or ? -dominated)
• Friedmann equation
• Universe exponentially expanding
• Infinitely old, infinite horizon distance

12
Inflation

• DE is fundamental in inflation (Guth 1981)
• Early period in the history of the Universe,
  when the expansion was accelerating outward

inflation
rad dominates
mat. dominates
? dominates
t
Inflation?
13
DE is not
14
What can be DE?

• Transient phenomenon, which will disappear in the
  future
• Cosmological constant (?CDM model)
• Scalar field (quintessence). ? is not constant,
  exhibits slow variation
• Modified gravity (Gauss-Bonet extradimensions)

15
(No Transcript)