# Presentation: 630942

## The Hunting of the Dark Energy

**and**
**On Beyond Lambda**
**Eric Linder**
**Cosmology Teach-In **
**26 June 2003**

## Cosmic Concordance

**Cosmic Concordance**

** *****Supernovae alone*****   ****	****       ******** Accelerating expansion**
** ******** ****> 0**
** *****CMB alone***
****** ****Flat universe **
****** ******** ****> 0 **
** *****Any two of SN, CMB, LSS***
****** ****Dark energy ~70%**

## Revolutions in Physics

**Lord Kelvin (1900): Two clouds on the horizon**

**The horizon is 95% cloudy!**

**Revolutions in Physics**

- STScI

## Supernovae map expansion

**Supernovae map expansion**

## Distance-redshift  a(t)

**Distance-redshift ******** a(t)**

## Supernovae: Mapping Expansion

## Supernovae: Acceleration

## Expansion map  d(z)

## Supernova Cosmology 1

**Supernova Cosmology 1**

## Supernova Cosmology 2

**In flat universe:  ********M****=0.28 [********.085 stat][********.05 syst]**** Prob. of fit to ********=0 universe: ****1%**

## Acceleration

## Negative pressure

## Dark Energy

**Acceleration of the universe can be caused within general relativity by negative pressure. **
**This can be from a ****dark energy****, **
**arising from the “springiness” of space,     i.e. from the quantum vacuum.  ****	****	****	****   *****cf.***** Einstein, deSitter, Weyl 1910s-1920s. **
**Is this mysterious dark energy the original cosmological constant, a quantum zeropoint sea?**** **

## The Hunting of the Dark Energy

**He had bought a large map representing the sea **
**Without the least vestige of land, **
**And the crew were much pleased when they found it to be**
**A map they could all understand. **
**-- Lewis Carroll, *****The Hunting of the Snark***

**Two flaws:**
** ****The sea level should be 10****120**** times the height of the land – it really should be a featureless sea! **
** ****The area of sea vs. land should evolve rapidly – why do we see it as 70:30 not all one or the other?  **

## Cosmological Constant 

**The energy scale of the vacuum needed to fit observations of the dark energy density (the sea level) is ****meV**** not ****M****pl**** ~ 10****19**** GeV**** **
**To try to correct the coincidence problem (neither all land nor all sea today), the effective mass of a varying quantum field must have a Compton wavelength ~ size of universe **
**m ~ H****0**** ~ 1/(10****28**** cm) ~ 10****-33**** eV**
**[L****pl****= 10****-33****cm] / 10****28**** cm = m / [10****19****GeV ]**

##  Fails

**Other maps are such shapes, with their islands and capes, **
**But we’ve got our brave [captain] to thank**
**(So the crew would protest) that he’s bought us the best – **
**A perfect and absolute blank. **
**-- Lewis Carroll, *****The Hunting of the Snark***

**The universe is not simple:**** **
**So maybe neither is the quantum vacuum ****	****      (or gravitation?)**

## So... On Beyond ! 

**On beyond ********! It’s high time you were shown**
**That you really don’t know all there is to be known.**** **
**-- ****à**** la Dr. Seuss, *****On Beyond Zebra***

**How do we find dark energy models inspired by fundamental physics?**
**How do we find the nature of dark energy through observations? **

## Dark Energy – Early Days 

**This is not new! **
** ****High energy physics models – Linde 1986 **
** ****Cosmological probes – Wagoner 1986 ****(plots by EL)**
** ****Cosmological observations – Loh & Spillar 1986**
**But**** observations were imprecise and inaccurate. Galaxy counts showed ********M**** ******** 1 but major difficulties with evolution. **
***12 years passed...****** ***

## Dark Energy – The Discovery 

****** ****> 0 at ****	****    99% confidence**

## Dark Energy – The Next Generation 

**Discovery +12 years**

**Supernova/Acceleration Probe: SNAP**

**Dedicated dark energy probe**

## Fundamental Physics

**Map the expansion history of the universe**

**The subtle slowing and growth of scales with time – ****a(t)**** – map out the cosmic history like the tree rings map out the Earth’s climate history. **

## Dark Energy at z > 1

**Robust parametrization:**** **** *****w(a)=w******0******+w******a ******(1-a)******	******       *****Community recognition: CMB*****fast*****, CMB*****easy****** ***
**Alterations to Friedmann framework ******** *****w(z)***
**Friedmann equation: **
**H****2**** = (8********/3) ********m**** + ********H****2****(z)**
**Effective equation of state:**
**w(z) = -1 + (1/3) d ln(********H****2****)/ d ln(1+z)**

**Time variation w**** ́ is a critical clue to fundamental physics.**

** ****Deep surveys of galaxies and SN to *****z>1***
** ****Large scale structure formation**
** ****CMB constraints from *****z******lss******=1100***** **

## Supernovae Probe Dark Energy

**SNAP tightly constrains dark energy models. **

## Complementarity

**SNAP+Planck have excellent  complementarity, equal to a prior ********(********M****)********0.01.  **
- Frieman, Huterer, Linder, & Turner 2002
**SNAP+Planck  can detect       time variation w**** ́ at 99% cl           ****(e.g. SUGRA)****. **

**SNAP tightly constrains dark energy models... ****And plays well with others.**

## Fundamental Physics 2

**SNAP tightly constrains dark energy models... And plays well with others.**** Lots of others. **

** ****Probing the nature of dark energy **
** ****Structure of the vacuum**
** *****w****** ́******(z) ************ V****** ́ ******/ V(************)***
** ****High energy physics**
** ****Synergy and complementary methods**

## SNAP Complements SNAP

**SNAP Complements SNAP**

**SN Ia**

**Weak Lensing**

**SN II**

**Clusters**

**Baryon Oscillations**

**Strong Lensing**

**Wide, Deep and Colorful**
** ****9000 times the area of Hubble Deep Field**
** ****15 sq.deg. to AB mag R=30 ; 120 epochs**
** ****300 sq.deg. to AB mag R=28**

## On Beyond 

**You’ll be sort of surprised what there is to be found Once you go beyond ******** and start poking around. **** **
**-- ****à**** la Dr. Seuss, *****On Beyond Zebra***

**Dark energy is...**
** ****Dark**
** ****Smooth on cluster scales**
** ****Accelerating**

**Maybe not completely! Clumpy in horizon? Maybe not forever!**

**It’s not quite so simple!**** **

## The Zoo Beyond Zebra

**Motivation: **
**	****Because it’s there?!**
**	****More natural than cosm-illogical constant?**
**Particle physics has zebrons, zebrillas, zebrinos...**
**Inflation has its hybrids, supernaturals, etc.**** **
**Quintessence has its mutations in attempt to make physics more natural. **
**Simplicity vs. naturalness – epicycles **

- Kolb

## Heart of Darkness

**Is dark energy dark – only interacts gravitationally?**
**Self interaction:**** **
**Scalar fields have radiative corrections leading to instability to self clumping: Qballs **
**	******** ****pseudoscalar quintessence **
**Axion quintessence, PNGB **
**Coupling to matter:**
**Leads to 5****th**** force: limited by lab tests **
**Unify dark energy with dark matter? **
**	**** ******** ****Chaplygin gas**** **
**Distorts matter power spectrum: ruled out unless within 10****-5**** of ******

**the horror! The horror!**

## Heart of Darkness 2

**Coupling to gravitation: **** **
**Scalar-tensor theories **
**	******** ****Extended quintessence**
**Can clump on subhorizon scales **
**Can “turn on” from nonlinear structure formation?!**
**Higher dimension gravity**
**	**** ******** ****Scalaron quintessence**
**Can be written in terms of scalar-tensor and w****eff**
**Same game as early universe inflation – just want to occur at late times, low curvature, potential, etc.**

## Heart of Darkness 3

**For flat, Robertson-Walker metric **
**R = 6 ( ****ä****/a + ****å****2****/a****2 ****) = 6H****2**** (1 – q)**
**So acceleration related to Ricci scalar**
**w****tot****= –(1/3) (R/3H****2**** – 1)**
**(also follows from R = -8********GT).**
**So acceleration for ****R > 3H****2****. But can’t get w****eff**** by ********R **
**like before with ********H, since changes field equations. **
***S = ************ d******4******x ************-g *****[***** R + L******M *****]**
**Can get acceleration by **
**Change RHS T********, e.g. dark energy**
**Add terms in R, e.g. modify gravity**
**Couplings or imperfect fluid *****L******M***

## Phantoms, Strings, and Branes

***w***** < -1:**** **
**Phantom energy**** – why not allow it? **
**Requires non-canonical kinetic energy, e.g. negative or nonlinear function. **
**	****k-essence, strings, branes**
**Ties to quantum gravity**
**	****e.g. vacuum metamorphosis**
**Fate of universe is not deSitter but superacceleration (if *****w***** stays < -1)**

## History and Fate

**Mapping the history of the expansion tells us the fate of the universe – if very precisely mapped.**

## Collapsing Universe

**To map out use of observations to probe fate of the universe, start with simplest model: **
**1 parameter linear potential**
**V(********) = V****0**** + ******** M****Pl****3 ******
**Eventually V(********) < 0 and universe collapses.**
**Inspired by supergravity models, fairly generic fit for any collapsing model.**** **
**How long until cosmic doomsday?**

- Work in collaboration with Renata Kallosh, Jan Kratochvil, Andrei Linde, Marina Shmakova

## Linear Potential

**These dark energy models look like ******** in the past, but develop a strong *****w****** ́*****. **

## Cosmic Doomsday

**By measuring *****w******0*****, *****w****** ́*****, SNAP will be able to limit the time until doomsday. **

**t****doom****= ******** (********)**
**t****doom**** > 28 Gyr [95% SNAP]**
**t****doom**** > 35 Gyr [95% SNAP+CMB]**
**t****doom**** > 35 Gyr [68% SNAP]**
**t****doom**** > 47 Gyr [68% SNAP+CMB]**

## On Beyond...

***w****** ́***** is the 1****st**** step for fundamental physics beyond ********.**
**Then *****w(z)*****. ****	****	****	****	****         Eventually spatial variations *****C******l******Q***** ?**
**In our hunt for the dark energy, the data decides how to go on beyond ********.**
**SNAP[SN] + SNAP[WL] + CMB (+...)**** tells us if**
**In the places I go there are things that I see ****	****	****  That I never could spell if I stopped with the Z**
**   ****-- Dr. Seuss, *****On Beyond Zebra***