Dark Matter Direct
Detection
And Applications of Effective Field
Theory
Gabriel Barello
University of Oregon GSS
Oct, 1. 2014
Dark Matter
• The
famous dark matter 2π chart:
map.gsfc.nasa.gov
• Why
do we think it exists?
Mpa-garching.mpg.de/g_lens
apod.nasa.gov
bustard.phys.nd.edu
WIMP Paradigm
•
If we have DM only interact gravitationally, everything works out great with a DM
mass near the EW scale
 Simplest Model – ΛCDM
 Measured - Ω𝐷𝑀 ℎ2 ~.112
 Freeze out - Ω𝐷𝑀 ℎ2 ~.1 ×
3×10−26 𝑐𝑚3 /𝑠
<𝜎𝜐>
 Weak Scale 𝜎𝜐 gives Ω𝐷𝑀 ℎ ~.1!
2
•
VERY INTERESTING – the EW scale is a big deal.
•
Simple (spin independent) WIMP DM satisfies pretty much all observational
motivations for DM.
Direct Detection
•
It better interact more than gravitationally if we’re ever
going to see it, we’re being optimistic.
•
“Lets put a big vat of Xenon underground and see if
anything hits it!
•
So much background…
•
There are many methods:





Phonons
Scintillators
Electron Capture
Bubble nucleation
Probably others…
A few examples
•
DAMA/LIBRA - (NaI)
•
KIMS
- (CsI)
•
COUPP
- (CF3I)
•
XENON/LUX - (Xe)
•
CoGeNT
- (Ge)
•
CDMS
- (Ge)
•
CRESST
- (CaWO4)
•
Others…
Did we see it?
•
DAMA Bernabi et. al.
DAMA –
 Modulation
•
CoGeNT –
 Modulation?
•
CRESST –
 Low Energy Excess
•
CDMS –
 Saw a few events.
CDMS Agnese et.al.
CoGeNT Aalseth et.al.
The current direct detection situation
•
LUX rules out everything (kinda)
•
A few ideas that seem to make life easier:
 Isospin dependent coupling (coupling only to protons)
 Iodine has an unpaired proton, which means it should interact more with DM that interacts
more with protons.
 Magnetic Dark Matter
 Iodine has a larger magnetic dipole moment than Xenon.
 Inelastic dark matter
 Makes heavier nuclei less sensitive, more relevant pre LUX.
 There are other things that I am not aware of
Thanks!
Or:
Switching gears
•
There are as many theories about DM as there are theorists.
 What is a physicist to do?
EFT in three slides
•
If there are particles in your theory that are too heavy to be created in your
system (because there isn’t enough energy) you can pretend they don’t exist!
•
At sufficiently low energies, their effects just look like a coupling constant
for a new interaction.
http://cds.cern.ch/record/1561006/files/FeynDiagr.png
Top Down vs. Bottom Up
•
Top Down:
 Start with a theory and “integrate out” high energy degrees of freedom.
 Example: Fermi Theory of weak interactions – Integrate out the weak gauge bosons.
 Used to Simplify
•
Bottom Up




Decide upon degrees of freedom you want
Choose a symmetry to preserve
Find a parameter that is small in the regime you’re interested in.
Write a lagrangian with every allowed term and arbitrary coefficients.
 “Everything not forbidden is compulsory” – M. Gell-Mann (Actually T.H. White, apparently)
 Example: The effective theory of DM direct detection!
 Used
EFT of dark matter direct detection
•
We can use effective theory to describe DM in the nonrelativistic limit interacting with
nucleons
 Connect to nuclear matrix elements, use nuclear theory to compute nuclear response.
𝑣
 Small parameter: 𝑐 ∼ 10−3
•
After determining the right effective, NR, theory you can use it to understand data without
using a UV model (bottom-up), or use it to easily compare your UV model to low energy data
(top-down).
•
Gives model independent insight into uncertainties, experimental design.
•
This has already been done for elastic collisions by Fitzpatrick, Haxton, Katz, Lubbers and
Xu. [1203.3542]
How to do it:
•
5 free parameters – 2 orthogonal 3-vectors
 𝑞 ≡ 𝑚𝑁 (𝑣𝑁2 − 𝑣𝑁1 ) ~ 𝑣
 𝑣⊥ = 𝑣𝑟 −
𝑞2
;
2𝜇
𝑣𝑟 = 𝑣𝜒1 − 𝑣𝑁1
 𝑞 ∙ 𝑣⊥ = 0
•
Galilean Invariance
•
This, along with small 𝑣 gives you 20 operators to first order
•
NR limit of all (elastic) relativistic effective operators can
be written in terms of these.
•
5
𝑖𝜒𝛾 𝜒𝑁𝑁 →
𝑞
−𝑖
𝑚𝜒
∙ 𝑆𝜒
Inelastic Dark Matter
•
Dark matter comes in, hits a nucleon, and emerges with more mass
 𝑚𝜒2 − 𝑚𝜒1 = δ
•
The “right” definition of 𝑣⊥ changes slightly
•
The kinematics change
 𝑣𝑚𝑖𝑛 𝐸𝑅 =
1
𝑚𝑁 𝐸𝑅
2 𝑚𝑁 𝐸𝑅 𝜇𝑁𝜒
+ 𝛿
•
We get a new small parameter: the mass splitting.
•
Don’t really get any novel low energy operators, but δ can appear as a
coefficient and some of the high energy
Aaand iDM still sneaks by
constraints:
G.B., S. Chang, C. Newby: 1409.0536