Indirect dark matter detection and the Galactic Center GeV Excess

Image Credit: Springel et al. 2008 Indirect dark matter detection and the Galactic Center GeV Excess Jennifer Siegal-Gaskins Caltech

Image Credit: Springel et al. 2008 Jennifer Siegal-Gaskins Caltech

Image Credit: NASA/DOE/International LAT Team Jennifer Siegal-Gaskins Caltech

How to detect particle dark matter? Direct!! Production (collider) Indirect SM SM 2

Indirect dark matter signals Credit: Sky & Telescope / Gregg Dinderman 3

Dark matter photon spectra soft channels = quarks, W, z 1.0000 0.1000 b b τ + τ hard channels = charged leptons (e, μ, τ) x 2 dn/dx 0.0100 W + W t t direct annihilation to photons = line emission (γγ, Zγ) 0.0010 0.0001 0.001 0.010 0.100 1.000 x=e/m χ Spectra calculated with PPPC 4 DM ID [Cirelli et al. 2010] 4

The dark matter annihilation signal intensity = particle physics term K astrophysics term J K ann = dn de h vi 2m 2 J ann ( ) = 1 4 Z los ds 2 (s, ) 5

The dark matter annihilation signal intensity = particle physics term K astrophysics term J K ann = dn de h vi 2m 2 J ann ( ) = 1 4 Z los ds 2 (s, ) spectrum of particles produced 5

The dark matter annihilation signal intensity = particle physics term K astrophysics term J K ann = dn de h vi 2m 2 J ann ( ) = 1 4 Z los ds 2 (s, ) dark matter particle mass 5

The dark matter annihilation signal intensity = particle physics term K astrophysics term J K ann = dn de h vi 2m 2 J ann ( ) = 1 4 Z average of pair annihilation cross section times relative velocity los ds 2 (s, ) 5

The dark matter annihilation signal intensity = particle physics term K astrophysics term J K ann = dn de h vi 2m 2 J ann ( ) = 1 4 Z los ds 2 (s, ) dark matter density 5

The dark matter annihilation signal intensity = particle physics term K astrophysics term J K ann = dn de h vi 2m 2 J ann ( ) = 1 4 Z los ds 2 (s, ) 5

Indirect dark matter signals particle mass clustering and annihilation cross-section annihilation channel Bertone 2007 6

The Fermi Large Area Telescope (LAT) launched June 2008 20 MeV to > 300 GeV angular resolution: ~ 0.1 deg above 10 GeV ~ 1 deg at 1 GeV primarily sky-scanning mode for first ~ 5 years, enhanced Galactic Center observation mode began in December 2013 Fermi data and analysis tools are public! Credit: NASA/General Dynamics 7

Dark matter annihilation signal Image credit: Springel et al. 2008 8

Dark matter signals from the Inner Galaxy 10 6 dark matter density profiles 10 5 dark matter density 3 10 4 10 3 10 2 10 1 10 0 10 1 0.1 deg inner regions: (r) / r 10 2 10 3 10 3 10 2 10 1 10 0 10 1 r Sun radius from Galactic Center r Pierre, JSG, & Scott, 2014 9

Dark matter signals from the Inner Galaxy angular dependence of dark matter intensity 10 6 (proportional to intensity) 2 5 1 10 4 10 2 15 pc inner regions: (r) / r 10 0 10 1 10 0 10 1 angle from Galactic Center Pierre, JSG, & Scott, 2014 10

A dark matter signal in the Inner Galaxy? (circles = sources) see: Hooper & Goodenough 2011, Abazajian & Kaplinghat 2012, Hooper & Slatyer 2013, Gordon & Macías 2013, Abazajian et al. 2014, Daylan et al. 2014, and others 11

A dark matter signal in the Inner Galaxy? Using Fermi LAT data, multiple groups have claimed an excess at a few GeV from the Galactic Center and higher Galactic latitudes. The excess has been interpreted as emission from dark matter (DM) annihilation and/or unresolved millisecond pulsars (MSPs). Energy spectrum of the excess: can be fit by DM with mass of ~10-40 GeV, depending on channel uncomfortably similar to MSPs Excess is spatially extended: if from annihilation, need steep DM density profile r - γ with γ = 1.2-1.4 (circles = sources) see: Hooper & Goodenough 2011, Abazajian & Kaplinghat 2012, Hooper & Slatyer 2013, Gordon & Macías 2013, Abazajian et al. 2014, Daylan et al. 2014, and others 11

A dark matter signal in the Inner Galaxy? Using Fermi LAT data, multiple groups have claimed an excess at a few GeV from the Galactic Center and higher Galactic latitudes. The excess has been interpreted as emission from dark matter (DM) annihilation and/or unresolved millisecond pulsars (MSPs). Energy spectrum of the excess: can be fit by DM with mass of ~10-40 GeV, depending on channel uncomfortably similar to MSPs Excess is spatially extended: if from annihilation, need steep DM density profile r - γ with γ = 1.2-1.4 uncertain if MSPs could explain large extension and steep profile (circles = sources) see: Hooper & Goodenough 2011, Abazajian & Kaplinghat 2012, Hooper & Slatyer 2013, Gordon & Macías 2013, Abazajian et al. 2014, Daylan et al. 2014, and others 11

A dark matter signal in the Inner Galaxy? Using Fermi LAT data, multiple groups have claimed an excess at a few GeV from the Galactic Center and higher Galactic latitudes. The excess has been interpreted as emission from dark matter (DM) annihilation and/or unresolved millisecond pulsars (MSPs). Energy spectrum of the excess: can be fit by DM with mass of ~10-40 GeV, depending on channel uncomfortably similar to MSPs Excess is spatially extended: if from annihilation, need steep DM density profile r - γ with γ = 1.2-1.4 uncertain if MSPs could explain large extension and steep profile To generate amplitude of the excess: (circles = sources) see: Hooper & Goodenough 2011, Abazajian & Kaplinghat 2012, Hooper & Slatyer 2013, Gordon & Macías 2013, Abazajian et al. 2014, Daylan et al. 2014, and others 11

A dark matter signal in the Inner Galaxy? Using Fermi LAT data, multiple groups have claimed an excess at a few GeV from the Galactic Center and higher Galactic latitudes. The excess has been interpreted as emission from dark matter (DM) annihilation and/or unresolved millisecond pulsars (MSPs). Energy spectrum of the excess: can be fit by DM with mass of ~10-40 GeV, depending on channel uncomfortably similar to MSPs Excess is spatially extended: if from annihilation, need steep DM density profile r - γ with γ = 1.2-1.4 uncertain if MSPs could explain large extension and steep profile To generate amplitude of the excess: requires roughly thermal relic DM annihilation cross section (circles = sources) see: Hooper & Goodenough 2011, Abazajian & Kaplinghat 2012, Hooper & Slatyer 2013, Gordon & Macías 2013, Abazajian et al. 2014, Daylan et al. 2014, and others 11

A dark matter signal in the Inner Galaxy? Using Fermi LAT data, multiple groups have claimed an excess at a few GeV from the Galactic Center and higher Galactic latitudes. The excess has been interpreted as emission from dark matter (DM) annihilation and/or unresolved millisecond pulsars (MSPs). Energy spectrum of the excess: can be fit by DM with mass of ~10-40 GeV, depending on channel uncomfortably similar to MSPs Excess is spatially extended: if from annihilation, need steep DM density profile r - γ with γ = 1.2-1.4 uncertain if MSPs could explain large extension and steep profile To generate amplitude of the excess: requires roughly thermal relic DM annihilation cross section (circles = sources) would require a few thousand MSPs, which seems plausible see: Hooper & Goodenough 2011, Abazajian & Kaplinghat 2012, Hooper & Slatyer 2013, Gordon & Macías 2013, Abazajian et al. 2014, Daylan et al. 2014, and others 11

A dark matter signal in the Inner Galaxy? Energy spectrum of excess in Galactic Center with bremsstrahlung m$ = 35 GeV $$ bb NB: Abazajian et al (2014) find strong dependence of spectrum of excess on details of background model Daylan et al. 2014 12

A dark matter signal in the Inner Galaxy? Excess is spatially extended γ = 1.4 (circles = sources) Daylan et al. 2014 13

Excess over what? What s in the model: Galactic diffuse emission associated with cosmic-ray interactions (sum of many processes) isotropic gamma-ray background (measured) detected gamma-ray sources (e.g., pulsars, supernova remnants) What s not in the model: unresolved gamma-ray sources Observed degrees Counts Fermi LAT data 0.69 0.95 GeV observed counts (circles = sources) degrees dark matter ls Abazajian & Kaplinghat 2012 14

Residuals (for best-fit model w/o dark matter component) 20 1-2 GeV residual 10 10 0-10 8 6 4 2 10-6 counts/cm 2 /s/sr -20 20 10 0-10 -20 0 Daylan et al. 2014 15

Residuals (for best-fit model w/o dark matter component) 20 1-2 GeV residual 10 10 0-10 dark matter? 8 6 4 2 10-6 counts/cm 2 /s/sr -20 20 10 0-10 -20 0 Daylan et al. 2014 15

Residuals (for best-fit model w/o dark matter component) 20 1-2 GeV residual 10 10 0-10 dark matter???? 8 6 4 2 10-6 counts/cm 2 /s/sr -20 20 10 0-10 -20 0 Daylan et al. 2014 15

Can the GeV excess be millisecond pulsars? best-fit to Fermi-detected MSPs spectral comparison GeV excess at high latitudes (data points) (circles = sources) Hooper, Cholis, Linden, JSG, Slatyer 2013 16

Can the GeV excess be millisecond pulsars? best-fit to Fermi-detected MSPs spectral comparison GeV excess at high latitudes (data points) (circles = sources) MSP spectrum similar but too soft at low energies Hooper, Cholis, Linden, JSG, Slatyer 2013 16

Can the GeV excess be millisecond pulsars? source count distribution ( b >10 deg) adopt a spatial model and luminosity function for the MSPs, calibrated to detections in radio base model can roughly account for the amplitude of Inner Galaxy excess, but strongly overpredicts number of Fermi-detected MSPs (circles = sources) Hooper, Cholis, Linden, JSG, Slatyer 2013 17

Can the GeV excess be millisecond pulsars? Source count distribution Latitude dependence of excess data model (circles = sources) adjusting MSP model parameters to better reproduce the observed source counts leads to models that cannot explain the amplitude of the observed excess Hooper, Cholis, Linden, JSG, Slatyer 2013 18

Multi-wavelength dark matter photon spectra DM spectrum from the Galactic Center 10-10 E [MeV] 10-3 10-1 10 1 10 3 10 5 secondary photon emission associated with charged particle final states: bremsstrahlung inverse Compton scattering of starlight, CMB synchrotron due to magnetic fields ν S(ν) [erg cm -2 s -1 ] 10-12 10-14 10-16 CHANDRA IC on starlight IC on CMB Synchrotron π 0 10-18 10 17 10 19 10 21 10 23 10 25 10 27 ν [Hz] Regis & Ullio 2008 19

Bed of Procrustes 20

Bed of Procrustes Lacroix, Boehm, Silk 2014 Lacroix et al. point out importance of: inverse Compton propagation model diffusion (and latitude dependence of secondary emission) 21

Is the GeV excess dark matter? 22

Is the GeV excess dark matter? Hard to (fully) explain with gamma-ray millisecond pulsars. Other source populations? 22

Is the GeV excess dark matter? Hard to (fully) explain with gamma-ray millisecond pulsars. Other source populations? Attributable to uncertainties in modeling of Galactic diffuse emission? 22

Is the GeV excess dark matter? Hard to (fully) explain with gamma-ray millisecond pulsars. Other source populations? Attributable to uncertainties in modeling of Galactic diffuse emission? Sum of several processes with not-strongly-constrained inputs: cosmic-ray spectra and distribution gas distribution interstellar radiation field magnetic fields 22