# Presentation: 119278

## Dark Matter & Dark Energy:New Challenges for Particle Physics

**Jim Siegrist**
**UCB/LBNL**
**USF, 29-Apr-04**
**Acknowledgement: Murayama, Hinchliffe, Quantum Universe Writing Team**

## What is the nature of the universe and what is it made of?What are matter, energy, space and time?How did we get here and where are we going?

**Understanding the Universe requires particle physics to determine its fundamental nature**
**Astrophysical obs ******** parameters of Universe**
**Accelerator expts ******** search for quantum explanation**
**Two ends must meet**
**Observing the relics of the big bang**
**Recreating the particles and forces of early Universe at accelerators**

**Particle Physics and the Quantum Universe**

## Particle Physics Has a Complete Understanding of Ordinary Matter

**We have a commanding knowledge of the particles and forces around us.**
**A theoretical framework called the ‘Standard Model’ (SM) describes data with exquisite precision.**

## Symmetry Plays the Central Role

**Symmetry Plays the Central Role**

- Formulation of the SM reveals that the laws of physics exist because of underlying (global, eg. space-time independent) symmetries:
- Translation invariance => momentum conservation
- Rotational invariance => angular momentum conservation
- Some symmetries have been ‘lost’ as the Universe has cooled from the Big Bang
- Particle masses arise because the vacuum today has different symmetry properties than during the initial fireball
- Space-time dependent (local, or gauge) symmetries generate the forces in the SM

***The Standard Model Framework indicates how it can be systematically extended***

## Recent Discoveries IndicateParticle Physics Has Reached a Singular Moment  

## A Revolution in Particle Physics: Some of the Open Issues

- What is Dark Matter?
- What is Dark Energy?
- Are there extra space dimensions?
- Do all the forces become one?
- What happened to the anti-matter?
- How did the Universe come to be?

***We know the Standard Model******is an incomplete description of the Universe***

## Dark Matter

**Astrophysical Perspective**
**Particle Physics Perspective**
**Models for new physics**
**Current and future work**

## Astrophysical Perspective – Galaxy Rotation Curves

**Scale 10KPc (30,000 light years)**
**Use Doppler shift of light from star in spiral galaxy to give velocity (red shift)**
**Expect velocity to fall off with distance from center**
**-**** ****...but it doesn’t**

## Dark Matter in Galaxy Clusters

- Galaxies form clusters bound in a gravitational well
- Hydrogen gas in the well gets heated, emits X-rays
- Can determine baryon fraction of the cluster
*	**	**f**B**h*3/2=0.0560.014
- Combine with the BBN
- matter*h*1/2=0.380.07
- Agrees with other methods

## Microlensing Searches

- Gravitational lensing effect

- Observed MACHO Event
- Symmetrical Light Curve and ‘one off’
- Gravitational: identical curves at different wavelengths (unlike variable stars)

## Particle Physics Perspective

**Big Bang Nucleosynthesis tells us the Dark Matter cannot be baryonic...**
**We are forced to introduce something beyond the Standard Model framework.**

## Particle Dark Matter

**Particle Dark Matter**

- It is not dim small stars (e.g., MACHOs)

- WIMP (Weakly Interacting Massive Particle) strongly favored
- Stable heavy particle produced in early Universe, left-over from near-complete annihilation
- TeV=1012eV the correct mass scale

## Cold Thermal Relics

- Dark Matter fraction increases as *M* increases
- Dark Matter fraction increases as ******* *decreases
- Interactions must be fully specified before a candidate can be ruled out. Calculations are therefore limited to those fully specified models.

- Figure from Kolb

## A Promising Model – Supersymmetry(SUSY)

- Additional symmetries have to be proposed to extend the SM to solve the Dark Matter problem
- One approach is to double the particle spectrum by positing a symmetry that links fermions to bosons...giving a sparticle paired with each SM particle, differing by 1⁄2 unit of spin
- Originally studied for other reasons...

## Problems Possibly ‘Solved’ by Supersymmetry

- Dark Matter problem – the lightest SUSY particle is stable => candidate for Dark Matter
- Explanation for how mass is generated in the SM => requires a heavy top quark, as was observed after the SUSY ‘prediction’

- Introduces a higher level of symmetry that stabilizes the theory against higher order corrections (solves the hierarchy problem)
- Provides for Unification of the forces into a single force at very high energies (alternatively, at very short distances or in the very early Universe)

## Standard Model and Supersymmetry

## Breaking Supersymmetry 

**How is supersymmetry broken?**
- Supergravity-inspired (mSUGRA):the typical benchmark
- parameters *m**1/2**, m**0**, A**0**, tan ****, sign(****)*
- radiative EWSB occurs naturally from large top mass
- the 01 is the LSP
- 01, 02, 1, sleptons and h are “light”
- 03, 04, 2, squarks and gluinos are “heavy”
- Many other possibilities have been studied

***i.e. *****SM particles plus two Higgs doublets and their SUSY partners**

## Opening the Door

**Once SUSY is introduced,**
**We can get *****started***** to discuss physics at shorter distances.**
**It opens the door to the next level:**
**	*****Hope to answer great questions***
**The solution to the Dark Matter problem itself, e.g., SUSY, provides additional probe to how the Universe works.**

## SUSY and Dark Matter

- Most SUSY models have unbroken R-parity that guarantees that lightest sparticle (LSP) is stable
- LSP must be neutral – candidates are *B W**0 **H **** *and *G*
* ***  is strongly disfavored by LEP and direct searches
- Parameters* **m*1/2 (gaugino masses), *m*0 (squark masses), tan* ***,* **sign(****)*, *A*, specified at GUT scale, fully describes model.
- LSP is usually *B* and mass controlled by m1/2

- ~  ~   ~ ~        ~

- ~

- ~

## SUGRA – Allowed Regions

- Plots are usually shown for fixed *tan ß sign *(μ), *A *as a region in *m*1/2 *m*0 space.

- Low mass region *m*1/2 and *m*0 are small

- 0.1  *h*2  0.3

## After WMAP Results

- Recall for LHC that roughly *m**g** **  *~*  *2.4*m*1/2* *and *m**e**  *~  1.1*m*0

- ~                                         ~

- LSP forced to lower masses by WMAP results – good for accelerator based searches.

## Current and Future Experimental Work

**Today –Tevatron**
**Soon – Large Hadron Collider**
**Tomorrow – Linear Collider**

## Tevatron

- bb (h/H/A) enhanced at large tanA  bb, so 4 b’s in final state
- A  ,
- Run I analysis: 4 jets, 3 b tags

**Tevatron**

- SUSY higgs A/H in , bb

- Run II 5 discovery: M=175 GeV for tan=50 with 5 fb-1

- Work in progress:
- Higgs multijet trigger studies
- 4 jets QCD background
- B-mistag studies for background

- Control sample requires two b-tags
- Data and MC agree very well

## Next Steps – LHC in 2007 

**The LHC detectors are designed to find the SM Higgs. Low mass is covered by ********, ttH(bb), qqH(WW*,********).  A low mass Higgs has many accessible decay modes ******** some couplings measured.**

## ATLAS Detector at CERN’s Large Hadron Collider

- Inner Tracking Detector

## ATLAS Overview

- Production is complete or in progress for most ATLAS components.
- Underground installation has been underway for some months.
- The schedule continues to be tight, but it is feasible for ATLAS to be ready for first LHC beam as planned in 2007.

- _[http://atlas.web.cern.ch/Atlas/TCOORD/Activities/TcOffice/Scheduling/Installation/UX15webcams.html](http://atlas.web.cern.ch/Atlas/TCOORD/Activities/TcOffice/Scheduling/Installation/UX15webcams.html)_

## LHC’s Task

**Find the particle(s) responsible for mass generation.**
**Could be Higgs, many Higgs’s, SUSY, Extra dimensions**
**Power of LHC is its enormous mass reach relative to current facilities.**
**Even low luminosity will open a new window.**
**10*****pb *****-1 ****(1 day at 1/100 of design luminosity) gives 8000 *****t************t*****  ****and 100 QCD jets beyond the kinematic limit of the Tevatron**
**If SUSY is correct, it could be found with ****100*****pb***** ****–1**

## How fast can SUSY be found at LHC?

- The LHC should be able to establish the existence of SUSY and open many avenues to study masses and decays of SUSY partices, if m(SUSY) is less than a few TeV.
- For example in the SUGRA model, the cosmologically interesting region of the SUSY search will be covered in the first weeks of LHC running, and the 1.5 to 2 TeV mass range for squarks and gluons will be covered within one year at low luminosity.

## The Linear Collider

**Full exploration of  SUSY requires the CERN LHC **
**A proton-proton collider with an energy seven times that of the Tevatron.**
**Together with a high-energy e+e- linear collider.**
**The LHC and a linear collider are both necessary to discover and understand the new physics at the TeV scale.**
**A coherent approach, exploiting the strengths of both machines, will maximize the scientific contributions of each.**

## Why Both a Hadron and Electron Collider?Precision Data 

**The present precision data were collected at hadron and electron machines.****  **
**The two probes provide complementary views – much like infrared and ultraviolet astronomy complement the optical.**

**We fully expect this theme to continue into the future.**

## How Will a 500 GeV Linear Collider Complement the LHC?

**Experiments at the LHC are likely to discover Dark Matter**
**But a linear collider answers crucial questions: **
**What is the spin state of the candidate?**
**Does it have the coupling consistent with Dark Matter particles?**** **
**Is it produced in a manner consistent with production of relics in the early Universe?**** **

***A fully International Project planned for the next decade***

## Dark Energy

-  Astrophysical Perspective
-  Particle Physics Perspective
-  Models and Ideas
-  Current and Future Work (for Supernovae)

## Type-IA Supernovae

- As bright as the host galaxy

## Type-IA Supernovae

- Type-IA Supernovae “standard candles”
- Brightness not quite standard, but correlated with the duration of the brightness curve
- Apparent brightness
- 	 how far (“time”)
- Know redshift
- 	 expansion since then

## What makes the supernova measurment special?

- An exhaustive accounting of sources of SN systematic uncertainities:

**SN Ia Evolution**
- shifting distribution of progenitor mass/metallicity/C-O
- shifting distribution of SN physics params:
- amount of Nickel fused in explosion
- distribution of Nickel
- kinetic energy of explosion
- opacity of atmosphere’s inner layers
- metallicity
**Gravitational Lensing (de)amplification**

**Dust/Extinction**
- dust that reddens
- evolving gray dust
- clumpy
- homogeneous
- Galactic extinction model
**Observational biases**
- Malmquist bias differences
- non-SN Ia contamination
- K-correction uncertainty
- color zero-point calibration

## Type-IA Supernovae

**Clear indication for “cosmological constant”**
**Can in principle be something else with negative pressure**
**With *****w*****=–*****p*****/**********, **
**Generically called “Dark Energy”**

## Cosmic Concordance

**CMBR: flat Universe**
******~1**
**Cluster data etc: **
******matter****~0.3**
**SNIA:**
**********–****2********matter****)~0.1**
**Good concordance among three**

## Constraint on Dark Energy

**Dark Energy is an energy that doesn’t thin much as the Universe expands!**

**Need negative pressure**
**Data consistent with cosmological constant *****w*****=*****p*****/**********=–1**

## Cosmic Coincidence Problem

**Why do we see matter and cosmological constant almost equal in amount?**
**“****Why Now” problem**
**Actually a triple coincidence problem including the radiation**
**If there is a fundamental reason for ****************~((TeV)****2****/*****M*****Pl****)****4****, coincidence natural**

- Arkani-Hamed, Hall, Kolda, HM

## Embarrassment with Dark Energy for Particle Physics

**A naïve estimate of the cosmological constant in Quantum Field Theory: ****************~*****M*****Pl****4****~10****120**** times observation**
**The worst prediction in theoretical physics!**
**People had argued that there must be some mechanism to set it zero**
**But now it seems finite???**

## Many ad-hoc Models to Explain Dark Energy

## Current and Future Work

**Nearby Supernova Factory/ SCP**
**SNAP**
**Some thoughts**

## Understanding Supernovae

**Supernova Cosmology Project**
**2003 Results: Higher redshifts,  ****	****	****   ****	****   ****	****	****   Greatly improved systematics checks**
**Ground based searches continuing: **
**Refining understanding (*****cf.***** CMAGIC:**** ********m****=0.08****)**** ****	**
**Probing averaged DE equation of state**** *****w     ******	******	*****Important, but will reach ground systematics limit ****	****    ****	****--can’t achieve robust**** *****w************ ******	******	******	******	******	*****--confusion limit in interpreting nature of DE**

**Understanding Supernovae**

## Nearby SN Factory follow-up Instrument

## Supernova/Acceleration Probe     

** ****Dedicated exploration of dark energy *****w(z)***
** ****Maps expansion history *****a(t)***
*** *****Reveals dark matter thru gravitational lensing**

**SNAP/JDEM: The Next Generation**

## SNAP/JDEM: The Next Generation

**SNAP is wide, ****deep****, and c****o****l****o****r****f****u****l**
** ****Essential to control systematics**
** ****Realized by LBNL technology CCDs**

- SNAP focal plane array

## SNAP: Fundamental Physics

** ****Space allows high *****z***** and systematics control **
** *****w****** ́******(z) ************ V****** ́ ******/ V(************)***
** ****High energy physics, extra dimensions, new gravity, inflation redux?**

## How can we solve the mystery of dark energy?

**A Dark Energy fills the vacuum of empty space**
**Accelerating expansion of Universe**
**Dark energy needs a quantum explanation**
**The Higgs field fills the vacuum of empty space**
**Gives particles mass**
**Are dark energy and the Higgs related?**
**SUSY a natural context for both**

***LHC, SNAP/JDEM and LC  are crucial tools for discovery***

## Cosmology and Particle Physicsmeet at TeV scale

**Dark Matter**
**Fermi (Higgs) scale**
***	******v*****~250GeV**
**Dark Energy**
**************~(2meV)****4**** *****vs***** (TeV)****2****/*****M*****Pl****~0.5meV**
**Neutrino**
**(*********m*****2****LMA****)****1/2****~7meV *****vs***** (TeV)****2****/*****M*****Pl****~0.5meV**
***TeV-scale physics will  be rich***

## Conclusions

**Conclusions**

**Answers to origins of Dark Matter and Dark Energy soon**
**Many exciting possibilities**
**One of several thrusts in particle physics today**

***Expect a 21******st******  Century Revolution in Particle Physics***

## References

- Books:
- The Elegant Universe, B. Greene, Random House, 1999.
- Supersymmetry, G. Kane, Perseus Publishing, 2000
- Quarks, Leptons and the Big Bang, J. Allday, IOP, 2002.
- Facts and Mysteries in Particle Physics, M. Veltman, World Scientific, 2003.
- The Fabric of the Cosmos, B. Greene, Knopf, 2004.
- Connecting Quarks with the Cosmos, National Academy Press, 2003
- Articles:
- Papers in the **Scientific American** special report on the cosmos (February 2004)
- 	“The Cosmic Symphony”, Wayne Hu and Martin White (p. 44)
- 	“Reading the Blueprints of Creation”, Michael A. Strauss (p.54)
- 	“From Slowdown to Speedup”, Adam Riess and Michael S. Turner (p. 62)
- 	“Out of the Darkness”, George Dvali (p. 68)
- Web sites:
- _[http://www.ostp.gov/](http://www.ostp.gov/)_ (see OSTP NEWS, *Physics of the Universe Report*)
- _[http://www.interactions.org](http://www.interactions.org/)_
- _[http://www.interactions.org/pdf/Quantum_Universe.pdf](http://www.interactions.org/pdf/Quantum_Universe.pdf)_
- Experiments:
- ATLAS _[http://atlas.web.](http://atlas.web.cern.ch/Atlas/Welcome.html)__[cern](http://atlas.web.cern.ch/Atlas/Welcome.html)__[.](http://atlas.web.cern.ch/Atlas/Welcome.html)__[ch](http://atlas.web.cern.ch/Atlas/Welcome.html)__[/Atlas/Welcome.html](http://atlas.web.cern.ch/Atlas/Welcome.html)_
- SNAP   _[http://snap.](http://snap.lbl.gov/)__[lbl](http://snap.lbl.gov/)__[.](http://snap.lbl.gov/)__[gov](http://snap.lbl.gov/)_
*	*

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