Lisa Randall

w/Matthew Buckley,

Yanou Cui,

Brian Shuve

For a long time WIMP “miracle” has

been the reigning paradigm

Now in position to test it fairly well

So far not looking promising

Though some hints…

Also particular models challenging to

make fit

SUSY heavy?

Worth asking if we really understand

dark matter

Does it interact as we might hope?

WIMP dark matter: Coincidence of energy carried by stable

weak scale particle and observed dark matter density

Another key observation: X~5 B

Why should dark matter and ordinary matter energy densities be at all comparable?

Could just be independently generated—baryogenesis somehow and weak miracle

On other hand, maybe clue their origin is in fact related

Xogenesis w/ Matthew Buckley

Asymmetric Dark Matter

Dark matter produced first

Weak scale dark matter still natural

Emergent Dark Matter and

Baryon/Lepton Numbers

w/Yanou Cui, Brian Shuve

Natural models explaining ADM

Alternative explanation: WIMPy

Baryogenesis w/Yanou Cui, Brian Shuve

WIMP annihilation trigger for

baryogenesis

WIMPs annihilate and lepton/baryon

number created together

ADM explains connection dark

matter and ordinary matter energy

densities

Matter and dark matter densities both

explained by asymmetries

Asymmetries connected: interaction

terms violating both B and X

Original models yield light DM

Xogenesis Create dark matter first

Transfer asymmetry from DM to matter

Can be weak scale

Nonrelativistic solution allows more

general possibilities

ADM establishes chemical

equilibrium between B or L and X

Net asymmetry prop

to chemical potential

Ratio chemical potentials~ratio

number densities~ratio energy

densities

More generally….

Number density suppressed for m>>T

In general, need to solve

Number density of X can be less than

that of B

Allows for different masses

Right ratio of densities found for wide range of m/T

Usually need m/T~10, which is quite reasonable

Expect comparable densities over the whole range

Sakharov Conditions:

Create X or B

X and B violating operators to

transfer asymmetry

Need symmetric component to be

eliminated

This might be best bet for detection.

Also possible to have B and X violation

and both created together

Then need to explain why they can have

comparable densities

•XB-Violation

•XL Violation

•Higher-Dim Op Suppressed by Weak Scale

Indirect signals unlikely

Mix with photon: see others’ work

Measure direct detection signal?

Symmetric component must annihilate

Model-dependent signal from doublet in

UV completion

Vector: annihilate to dark (eg W’s)

Generally can have entire DM sector

Bad: invisible

Detection not guaranteed

Relies on model-dependent annihilation

generally

Not ADM operators themselves

Chief nonobvious assumption: Symmetry-transferring, breaking operators

Sphaelerons might be most obvious-just need doublets—but hard to meet detection bounds

Existing ADM models employ higher dimensional operator involving weak scale suppression Least compelling aspect

Operators don’t shout out at you

UV completion requires additional structure

Certainly possible natural

Just not obvious

Detectability not guaranteed Symmetric component can annihilate into dark sector

Heavy dark matter gives weaker signal

On the other hand: natural, and explains weird near-coincidence of matter densities

And can still be connected to weak scale where we expect new matter

ADM compelling

But origin of operators that mix two

sectors?

Higher-dimensional operators can

violate both L (or B) and DM

numbers

Don’t necessarily expect L, X

conservation in early universe

Are B and X conserved?

Do we need to invoke new operators

Keep in mind we need these operators

only in early universe

Suppose normalizable mass mixing or mass

mixing generated by Planck-suppressed ops

No odd ops, no odd scales

B and X accidental symmetries!

w/Cui, Shuve

XL mixing in early universe to

transfer asymmetry--but must turn off

B, L, and X conserved at late times

Option I: Dynamical mechanism:

Φ is a scalar field

ΦXL turns on mass when vev turns on

Key is VEV that switches

Turns on, then off

Opposite to usual transition, but

readily happens in early universe eg

Multifield models-akin to hybrid inflation

Moduli fields, flat directions that roll to

zero

Option 2 Early universe kinetic terms,

Three Models

Order from more specific and less

specific parameters to less specific

model and more specific parameters

2 Higgs

Moduli-driven

Thermal Background

Get mass mixing: interplay of

neutrino-like oscillation and thermal

interaction

and new way to accommodate heavier

mX ...

Rapid shutoff of Φ triggered by

interaction with another scalar:

As with hybrid inflation

Two Stage Phase Transition in Two

Higgs Models

X dark matter, Yukawa mixing term, Z2 symmetry

Φ VEV first

H VEV later on

With temperature corrections:

Two step phase transition

At high temperature, all VEVs vanish

At critical temperature turns on h

vanishing

induces mass XL mass mixing

At second critical temperature, new

minimum develops

h turns on

tunnels to zero

This is true vacuum today

Direct Detection: Loop-suppressed

Can also look directly for second doublet

Now VEV doesn’t carry SU(2)

Dark matter neutral

So lepton-number carrying field neutral:

Χ

Simplifying assumption: Dirac

leptogenesis to get lepton number into

singlet

now modulus: induces mass

mixing as before

Need mixing at leptogenesis time to determine transfer

Φ rolls to its minimum

En route leptogenesis occurs

Lepton asymmetry shared with DM

Amount of transfer depends on value

of Φ field at leptogenesis time

Can get lower dark matter number

density relative to lepton number

when field has rolled to lower values

•Nothing assumed in this model except fields

•These operators should occur

•Global symmetries expected to be violated at

Planck scale)

•Furthermore early universe is hot

Two of Sakharov conditions (B and

CP violation) assumed in Lagrangian

Third dynamical—

Need to be out of equilibrium

eg out of equilibrium decay

Another possibility: WIMP freezeout

is source of out of equilibrium

behavior

WIMP annihilation directly (or

indirectly) leads to lepton [baryon]

production

DM/B near concidence explained

without ADM

Dark matter obtained as usual in

WIMP paradigm with order unity

couplings and weak scale dark matter

Baryon asymmetry created by

annihilations themselves

DM annihilates; B number created

Reverse can also occur

So washout plays a critical role

Essentially baryon number created

when washout decouples

Baryon density proportional to dark

matter density at washout freezeout

Implies washout decoupling must happen

before dark matter annihilation

decoupling

Guarantees number density of dark

matter less than that of baryons

Aside: weak scale baryogenesis

Bonus: no issue with reheat temperature

Need washout to freeze out first

Implies annihilation channel should

involve field heavier than DM

Guarantees kinematic suppression

Also: final state field mass must

(obviously) be less than twice dark

matter mass

Baryon number shouldn’t be washed

out by late decays, etc of exotic field

Need exotic field to decay into light

neutral object that carries baryon

number but doesn’t disturb visible

baryon density

WIMPy baryogenesis

Creates dark matter density inversely

proportional to annihilation cross

section

As conventional

Baryon density proportional to dark

matter density AT WASHOUT

FREEZEOUT

For

decay

Compare to leptogenesis via S decay

Question is whether S decays in or out of

equilibrium

If we assume S is weak scale, requires tiny

coupling .000001

Same sorts of interference: multiple S states, etc

But here baryon production from off-shell S via

Annihilating dark matter

Similar to leptogenesis

Differences

No constraint for completion before

sphaeleron temp

Can decay with true B violation or

preserving U(1) as with lepton case

Decay

either

Or

Clearly dark matter experiments telling us something

If we find evidence soon could be great vindication of WIMP scenario

If we don’t we’ll still want to know what it means

Perhaps we have been too focused on conventional WIMPs?

Other coincidences worth exploring and explaining

ADM

Xogenesis (weak scale)

Emergent

WIMP annihilation connected to leptogenesis or baryogenesis

Usually tradeoff between generiticity of model and parameter space

Admittedly much more challenging for experiment

But nature ultimately decides…