direct detection of sidm - harvard...
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Direct detection of SIDM
Sean Tulin w/ Manoj Kaplinghat & Haibo Yu
[1308.0618 + in progress]
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Particle physics of SIDM
• Dwarf scale anomalies point toward large cross section for DM particle c
• Typical WIMP: s ~ 1 pb, mc ~ 100 GeV
• Suggests dark force mediator f much lighter than weak scale
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Particle physics of SIDM
• Light mediator gives efficient annihilation channel for relic density:
– Symmetric or asymmetric DM
• Light mediator means self-interaction is
velocity dependent (like Rutherford scattering)
– Self-interacting DM in dwarf halos (v ~ 30 km/s)
– Collisionless DM in larger halos (e.g. v ~ 3000 km/s for Bullet Cluster)
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Light mediators in the dark sector
What do self-interactions have to do with direct detection?
What happens to the light mediator f?
– Assume decays to SM particles before BBN
– Simplest scenario (doesn’t affect cosmology)
c c c c
c c f f DM self-scattering DM direct detection
f f
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Light mediators in the dark sector
Decay f SM fermions before BBN – Maximum lifetime for f to decay ~ 1 second – Minimal coupling between dark sector and SM – Lower bound on direct detection cross section
Direct detection cross section – Suppressed by tiny coupling (long f lifetime) – Enhanced by light mediator mass ~ 1 – 100 MeV
Generically expect f coupled to SM What is the reach of direct detection for SIDM?
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Direct detection Current XENON100 Recent CDMS-Si (3 events)
Exciting/confusing time! Future limits: XENON1T, LUX, CDMS-lite, SuperCDMS, PandaX, …
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SIDM and direct detection
Self-interactions change phase space distribution of DM halo
Vogelsberger and Zavala (2012)
O(10%) effect on DM recoil rate in direct detection experiments Also effect annnual modulation amplitude and phase
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Simplified models for SIDM • DM c is a Dirac fermion
• Mediator f is a real scalar or vector
• Self-interactions through a Yukawa potential
, where
• Calculate parameter space for SIDM vs ac, mc, mf, and v (relative velocity)
ST, H.-B. Yu, K. Zurek (2012 + 2013); see also Buckley & Fox (2010)
See also Bellazzini, Cliche, Tanedo (2013)
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Portals to the dark sector
1. Vector mediator (f mixes with Z or g)
• Kinetic mixing with photon
• Z mass mixing (eZ is Z-f mixing angle):
2. Scalar mediator
• Higgs mixing (eh is h-f mixing angle)
(Assume e << 1, mf ~ 1 – 100 MeV << mZ)
Holdom (1984); Pospelov et al (2007); Arkani-Hamed et al (2009); Lin et al (2011) …
Babu et al (1997); Davoudiasl et al (2012) …
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Portals to the dark sector
• Kinetic mixing with photon
– No photon mass
– No coupling of photon to DM (no millicharged DM)
– Couple mediator f to SM fermions with EM charge
• Mixing with Z boson
– Couple mediator f to weak neutral current
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Portals to the dark sector
Want f to decay before BBN time ~ 1 second
Focus on vector mediator only (work in progress)
Lifetime (similar for both kinetic and Z mixing):
Final states:
• Kinetic mixing: f decays to all e+e-
• Z mixing: f decays mostly to neutrinos
(Neutrino-rich indirect detection signals)
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Constraints on kinetic mixing
Dent, Ferrer, Krauss (2012)
Beam dump experiments
SN1987A cooling arguments
Post BBN decays
Direct searches
SIDM region
Kinetic mixing case very constrained for SIDM: eg ~ 10-10 (!)
Different (weaker?) constraints for Z mixing case
eg
mf
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Parameterize f-nucleon coupling as: eeeff Spin-dependent DM-nucleon direct detection cross section (q2 = 0 limit):
Interaction portal with SM governed by eeff • Kinetic mixing: eeff = eg (Z/A) • Z mixing: eeff = 0.35 eZ (N/A)
XENON100 limits approaching 10-45 cm2
Sensitivity to eeff ~ 10-10 (Interesting for BBN limit!)
Direct detection
Note: two cases are isospin-violating Frandsen et al (2011)
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Direct detection implications for SIDM Solving small scale anomalies puts a constraint on direct detection.
Fixed s/mc = 1 cm2/g on dwarf scales Kinetic mixing with fixed eg = 10-9
ac = 10-3, 10-2.5, 10-2, 10-1.5, 10-1
mf and ac fixed by self-interactions Smaller ac compensated by smaller mf
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Parameter space for symmetric SIDM • Three parameters: (ac, mc, mf)
• Relic density determined by usual freeze-out (fixes ac)
• CMB constraint on DM annihilation
mc > 30 GeV*BR(f e+e-)
• Self-interactions in dwarfs to solve small scale anomalies
• Constraints from halo shapes (ellipticity of group halos)
• Bullet cluster constraint
for v ~ 30 km/s
Galli et al (2009); Slatyer et al (2009); Lopez-Honorez et al (2013)
for v ~ 300 km/s Peter et al (2012)
Vogelsberger et al (2012); Rocha et al (2012)
for v ~ 3000 km/s Randall et al (2007)
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Parameter space for symmetric SIDM
SIDM region for solving dwarf anomalies Wide range of DM mass Mediator ~ 1 – 100 MeV Assume dwarf halos with characteristic velocity v0 = 30 km/s
Peaks are where DM self-scattering has quantum mechanical resonances (bound states)
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Parameter space for symmetric SIDM
SIDM region for solving dwarf anomalies Assume dwarf halos with characteristic velocity v0 = 100 km/s i.e. LSB’s
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Parameter space for symmetric SIDM
SIDM region for solving dwarf anomalies
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Parameter space for symmetric SIDM
SIDM region for solving dwarf anomalies
Velocity-independent cross section
Velocity-dependent cross section
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Parameter space for symmetric SIDM
Shaded region: solve dwarf anomalies Halo shape bound
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Parameter space for symmetric SIDM
Shaded region: solve dwarf anomalies Halo shape bound Direct detection
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Parameter space for symmetric SIDM
SIDM coupled via kinetic mixing Shaded region: solve dwarf anomalies Halo shape bound Direct detection
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Parameter space for symmetric SIDM
SIDM coupled via kinetic mixing Shaded region: solve dwarf anomalies Halo shape bound Direct detection CMB constraint
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Parameter space for symmetric SIDM
SIDM coupled via Z mixing Shaded region: solve dwarf anomalies Halo shape bound Direct detection CMB constraint
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Parameter space for symmetric SIDM
SIDM coupled via Z mixing Shaded region: solve dwarf anomalies CMB constraint Halo shape bound Direct detection
CDMS-Si best fit region
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Parameter space for asymmetric SIDM • Three parameters: (ac, mc, mf)
• Require sufficient annihilation for fixed ac
• No constraints on annihilation (only c present after freezeout)
• Self-interactions in dwarfs to solve small scale anomalies
• Constraints from halo shapes (ellipticity of group halos)
• Bullet cluster constraint
for v ~ 30 km/s
for v ~ 300 km/s Peter et al (2012)
Vogelsberger et al (2012); Rocha et al (2012)
for v ~ 3000 km/s Randall et al (2007)
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Parameter space for asymmetric SIDM
Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster
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Parameter space for asymmetric SIDM
Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster
Velocity-independent cross section
Velocity-dependent cross section
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Parameter space for asymmetric SIDM
Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster
s/m < 0.1 cm2/g
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Parameter space for asymmetric SIDM
Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster
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Parameter space for asymmetric SIDM
SIDM coupled via kinetic mixing Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster Direct detection
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Parameter space for asymmetric SIDM
SIDM coupled via kinetic mixing Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster Direct detection
Larger eg to explain CDMS-Si region
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Parameter space for asymmetric SIDM
SIDM coupled via kinetic mixing Shaded region: solve dwarf anomalies Halo shape bound Bullet cluster
High mass region excluded for larger eg Low mass region probed by direct detection via electron recoil Essig et al 2010
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Conclusions (part 1)
• Simplified model: DM c + vector mediator f
• Anomalies on dwarf scales: mf ~ 1 – 100 MeV
• Although SIDM may be decoupled from direct detection, expect DM-SM coupling at some level
• Light mediator means direct detection sensitive to very small DM-SM couplings
• Current & future direct detection exploring “BBN parameter region” (f SM before BBN)
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Conclusions (part 2) • Direct detection complementary to astrophysics
– Constraints on large scales (e.g. Bullet Cluster) constrain SIDM at low DM mass (constant s)
– Direct detection constrain SIDM at WIMP-scale masses (corresponding to v-dependent s)