The 26th International Workshop on Weak Interactions and Neutrinos (WIN 2017) Dark matter velocity spectroscopy Ranjan Laha Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) Stanford University SLAC National Accelerator Laboratory Thanks to my collaborators: Tom Abel, John F Beacom, Kenny C Y Ng, Devon Powell, Eric G Speckhard arXiv: 1507.04744 Phys. Rev. Lett. 116 (2016) 031301 arXiv: 1611.02714 Phys. Rev. D95 (2017) 063012
Contents ü Introduction to dark matter ü Signal and background in dark matter indirect detection ü Dark matter velocity spectroscopy • General technique • Example: application to the 3.5 keV line Ranjan Laha
Introduction to Dark matter Ranjan Laha
The present Universe as a pie-chart WMAP website Most of the Universe is unknown Finding this missing ~ 95% is the major goal of Physics We concentrate on dark matter
Gravitational detection of dark matter Begeman, etal. MNRAS 249 (1991) 523 A Riess website Dwarf galaxies Astronomy Picture of the Day WMAP website http://www.dailygalaxy.com/my_weblog/2015/08/ dark-energy-observatory-discovers-eight-celestial- objects-hovering-near-the-milky-way.html Real observation from Hubble eXtreme Deep Field Observations : left side Dwarf galaxies Mock observation from Illustris : right side Illustris website 1405.2921
Gravitational evidence of dark matter at all scales Dark matter is the most economical solution to the problem of the need of extra gravitational potential at all astrophysical scales Many different experiments probing vastly different scales of the Universe confirm the presence of dark matter Modifications of gravity at both non-relativistic and relativistic scales are required to solve this missing gravitational potential problem --- very hard --- no single unified theory exists Credit: Carsten Rott, Basudeb Dasgupta
What do we know? • Structure formation tells us that the particle must be non-relativistic • Experiences “weak” interactions with other Standard Model particles • The lifetime of the particle must be longer than the age of the Universe
What do we want to know? • Mass of the particle • Lifetime of the particle • Interaction strength of the particle with itself and other Standard Model particles
Indirect detection of dark matter Credit: Carsten Rott Search for excess of Standard Model particles over the • expected astrophysical background e + γ ν p Credit: Carsten Rott Spectral features help --- astrophysical Flux • backgrounds are relatively smooth --- nuclear and atomic lines problematic Energy Targets: Sun, Milky Way (Center & Halo), Dwarf galaxy, • Galaxy clusters Ranjan Laha
Signal and background in indirect detection
Signals: continuum, box, lines, etc. Bringmann & Weniger � 2012 � Various types of signal: � E � E � 0.15 10 � E � E � 0.02 Continuum ΓΓ Box 1 x x 2 dN � dx o b q q , Z Z , W W Virtual internal bremsstrahlung VIB 0.1 Line 0.01 0.02 0.05 0.10 0.20 0.50 1.00 2.00 x � E � m Χ Z, W + W − → hadronisation / decay → γ , e + , ¯ q, Z ¯ χχ → q ¯ p, ν Continuum: Distinct kinematic signatures χχ → φφ ; φ → γγ Box: important to distinguish from backgrounds �� → ` + ` − � Virtual internal bremsstrahlung: Line: ν s → νγ χχ → γγ Ranjan Laha
Backgrounds: astrophysical, instrumental Due to the faint signal strength, astrophysical backgrounds can easily mimic the dark matter signal Instrumental features can mimic signal O’Leary etal., 1504.02477 Fermi-LAT 1305.5597 Ongoing controversy about the origin of the 3.5 keV line: dark matter or astrophysical Ranjan Laha
Confusion between signal and background • Confusion between signal and background is prevalent in dark matter indirect detection • Kinematic signatures are frequently used to distinguish between signal and background • Is there a more distinct signature that we can identify? • Yes, use high energy resolution instruments to see the dark matter signal in motion Ranjan Laha
Dark matter velocity spectroscopy Phys. Rev. Lett. 116 (2016) 031301 (Editors’ Suggestion) arXiv 1507.04744 Ranjan Laha
Dark matter velocity spectroscopy Galactic Longitude • Dark matter halo has little angular LOS Velocity momentum Detector Bett, Eke, etal., “The angular momentum of cold 0 dark matter haloes with and without baryons”; Kimm etal., “The angular momentum of baryons Blue Shift and dark matter revisited” • Sun moves at 0 Speckhard etal., 1507.04744 ~220 km/s Dark Gas 𝑤 � = 0 ⃗ Matter χ Gas • Distinct GC GC longitudinal dependence of signal Sun Sun • Doppler effect Ranjan Laha
Order of magnitude estimates v LOS ⌘ ( h ~ v χ i � ~ v � ) · ˆ r LOS h ~ v χ i is negligible in our approximation v � ≈ 220 km s � 1 For v LOS ⌧ c, δ E MW /E = � v LOS /c δ E MW ( l, b ) /E = +( v � /c ) (sin l ) (cos b ) δ E MW ≈ 10 − 3 E sign( � E MW ) ∝ sin l, for l ✏ [ − ⇡ , ⇡ ] Ranjan Laha
Example with dark matter decay Line of sight dI ( ψ , E ) dN ( E ) Differential Γ Z intensity = ds ρ χ ( r [ s, ψ ]) 4 π m χ dE dE Dark matter profile = Dark matter decay rate Γ Dark matter mass Energy spectrum dN ( E ) /dE is independent of dark matter profile modified energy spectrum Gaussian d ˜ N ( E, r [ s, ψ ]) dE 0 dN ( E 0 ) Z G ( E − E 0 ; σ E 0 ) = dE dE 0 total mass inside a radius r’ σ E = ( E/c ) σ v LOS Z R vir G dr 0 ρ χ ( r 0 ) M tot ( r 0 ) σ 2 v,r ( r ) = ρ χ ( r ) r 0 2 r width of Gaussian ds ρ χ ( r [ s, χ ]) d ˜ dN ( E ) 1 Z 1 N ( E − δ E MW , r [ s, ψ ]) d J Z ds ρ χ ( r [ s, χ ]) replaces dE = dE R � ρ � R � ρ � dE Ranjan Laha
Instruments with energy resolution ∼ O (0 . 1)% Hitomi/ Astro-H INTEGRAL/ SPI E ≈ 1 . 7 eV σ E Present Past 2.2 keV (FWHM) at 1.33 3 . 5 keV MeV http://www.cosmos.esa.int/web/ integral/instruments-spi Future Micro-X FWHM of 3 eV at 3.5 keV Figueroa-Feliciano etal. ATHENA includes noise 2015 contribution ATHENA X-IFU HERD: High Energy Cosmic Radiation Detection 1608.08105 from simulations Energy resolution for electrons and gamma will be < 1% at 200 GeV Wang & Xu Progress of the HERD detector Ranjan Laha
Sterile neutrino Abazajian 1705.01837 See talk by Totzauer in WIN 2017 Hansen and Vogl 1706.02707 E γ = m s ν s → ν a + γ 2 ⇣ m s Γ γ ≈ 7 × 10 − 33 s − 1 sin 2 2 θ ⌘ 5 10 − 10 keV An excellent dark matter candidate --- right handed component of the active neutrino Production scenarios: Dodelson - Widrow mechanism (similar to vacuum oscillations of neutrinos) Shi – Fuller mechanism (similar to MSW transitions of neutrinos) Ranjan Laha
Application to 3.5 keV line
3.5 keV ν s → ν a + γ Bulbul etal., Bulbul etal., 1402.2301 1402.2301 Sterile neutrinos? Bulbul etal., Baryonic 1402.2301 astrophysics? Stacking of 73 galaxy clusters Redshift z = 0.01 to 0.35 4 to 5 σ detection with XMM-Newton and 2 σ in Perseus with Chandra 2.3 σ in Perseus with XMM-Newton Bulbul etal., 1402.2301 3 σ in M31 with XMM-Newton Combined detection ~ 4 σ Conflicting results in many different studies Slide idea: Shunsaku Horiuchi Ranjan Laha
3.5 keV controversy Riemer-Sorensen 2014 Milky Way via Chandra ✗ (Contested by Bulbul etal., 2014 and Boyarsky Jeltema and Profumo 2014 Milky Way via XMM-Newton ✗ etal., 2014) Boyarsky etal. 2014 Milky Way via XMM-Newton ✓ Anderson etal., 2014 Local group galaxies via Chandra and XMM-Newton ✗ Malyshev etal., 2014 satellite dwarf galaxies via XMM-Newton ✗ Abazajian 1403.0954 Tamura etal., 2014 Perseus via Suzaku ✗ Babu and Mohapatra 1404.2220 Dutta etal. 1407.0863 Urban etal., 2014 Perseus via Suzaku ✓ Urabn etal., 2014 Coma, Virgo, and Ophiuchus via Suzaku ✗ Hofman etal., 2016 33 clusters ✗ Carlson etal., 2014 morphological studies ✗ HITOMI 2016 Perseus cluster ✗ Philips etal., 2015 super-solar abundance ✗ Shah etal., 2016 Laboratory ✗ Iakubovskyi etal., 2015 individual clusters ✓ Conlon etal., 2016 Perseus ✓ Jeltema and Profumo 2015 Draco dwarf ✗ Gewering-Peine etal., 2016 Diffuse ✗ Bulbul etal., 2015 Draco dwarf ✓ Cappelluti etal., 2017 Diffuse ✓ Franse etal., 2016 Perseus cluster ✓ Bulbul etal., 2016 stacked cluster ✓ Ranjan Laha Slide idea: Shunsaku Horiuchi and Kenny C Y Ng
Solutions to the 3.5 keV line controversy? Micro-X • Wide field of view Rocket ~10 -3 energy resolution near 3.5 keV Figueroa-Feliciano etal. 2015 SXS – Hitomi (Astro-H) • Narrow field of view Satellite ~10 -3 energy resolution at ~3.5 keV Lost due to technical failure Ranjan Laha Slide idea: Kenny C Y Ng
Looking at clusters Bulbul etal. 1402.2301 Dark matter line broader than plasma emission line Plasma emission lines are broadened by the turbulence in the X- ray emitting gas Ranjan Laha
Rotation of baryonic matter Radial velocity of gas as measured by 26 Al 1808.65 keV line Measurement by INTEGRAL/ SPI Kretschmer etal., 1309.4980 Galactic Longitude LOS Velocity Detector 0 Blue Shift 0 Follows the trend explained earlier Kretschmer etal., 1309.4980 𝑤 � ⃗ χ Ranjan Laha
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