DARK MATTER INTERACTIONS - PDF Free Download

DARK MATTER INTERACTIONS Jonathan H. Davis Institut d Astrophysique de Paris jonathan.h.m.davis@gmail.com LDMA 2015 Based on J.H.Davis & J.Silk, Phys. Rev. Lett. 114, 051303 and J.H.Davis, JCAP 03(2015)012

DARK MATTER INTERACTIONS WITH PHOTONS Many models of Dark Matter include an interaction with photons. Milli-charged DM Composite Particles Photon Dark Photon + -

DARK MATTER INTERACTIONS WITH PHOTONS Many models of Dark Matter include an interaction with photons. What signals would this Dark Matter lead to? Milli-charged DM Composite Particles Photon Dark Photon + -

DARK MATTER INTERACTIONS WITH PHOTONS Strong constraints exist on the charge that DM particles can have. For example: DM must decouple from baryons before the CMB is formed, to prevent Silk damping for the DM. PRD 83, 063509 (2011) However the only strong bound directly on the DMphoton scattering cross section is from the CMB. R. J. Wilkinson, J. Lesgourgues, and C. Boehm, JCAP 04 (2014) 026

DARK MATTER IN GALAXIES Early-universe probes are strong, but place bounds only at one particular photon frequency. Can we potentially observe DMphoton scattering at other frequencies? Can we observe DM-photon scattering in galaxies? DM Halo

DARK MATTER - PHOTON SCATTERING IN GALAXIES Observer DM-photon interaction Disc light Light from the bright central part Line of Sight h r r d Disc of the disc scatters with DM in the halo. DM Halo This could lead to a brightening at larger radii.

DARK MATTER - PHOTON SCATTERING IN GALAXIES In a distance dl there are dl σn DM (r) scattering events. Observer DM-photon interaction Disc light Line of Sight r Disc Hence the flux of scattered photons is an integral over the line of sight. h r d dl σndm (r)l d (h, r d ) Φ(θ e, φ e )= 4πl 2

DARK MATTER - PHOTON SCATTERING IN M101 dl σndm (r)l d (h, r d ) Use this to generate a map of the scattered light on the sky. Φ(θ e, φ e )= 4πl 2 However a radial profile is clearer...

DARK MATTER - PHOTON SCATTERING IN M101 Observer Dark Matter scattering with photons leads to a brightening of the DM-photon interaction Disc light observed image towards larger radii. Line of Sight r Disc h r d -23 10 cm 2 x (m/gev)

CHALLENGES TO OBSERVING DM-PHOTON SCATTERING The detection of faint light from DM-photon scattering is limited by the sensitivity of the instrument. Observing the galaxy faceon makes the DMscattering signal difficult to distinguish from emission in the stellar halo.

IMPROVING THE SENSITIVITY TO DM-PHOTON SCATTERING Can we observe this scattered light even for much smaller cross sections? A signal from DM-photon scattering may be easier to separate from the stellar halo background at longer wavelengths. Also interesting as earlyuniverse constraints are only at short wavelengths.

IMPROVING THE SENSITIVITY TO DM-PHOTON SCATTERING Other ways to improve sensitivity: Statistical analysis of multiple galaxies. Look for a correlation with the DM distribution. Looking at galaxies which are not face-on, to reduce emission from the disc. Perhaps using other astrophysical objects like AGN cores, though this would require greater angular resolution.

SUMMARY SO FAR Scattering of Dark Matter with photons is difficult to probe directly. Dark Matter-photon scattering could be observed in galaxies as the DM particles scatter light out from the centre of the galaxy to larger radii. This would contribute to an extra glow at the outskirts of galaxies. Measurements at multiple wavelengths could allow this signal to be separated from backgrounds such as emission from a stellar halo. Observer DM-photon interaction Disc light Line of Sight r Disc h r d

Direct Detection of Dark Matter DM Halo Dark Matter exists in a roughly spherical and non-rotating halo. Luminous matter exists in a disc rotating at around 200 km/s.

Direct Detection of Dark Matter DM Halo This relative rotation and the random motion of the DM particles results in a relative velocity between Earth and DM. DM Flow Sun Dark Matter exists in a roughly spherical and non-rotating halo. Luminous matter exists in a disc rotating at around 200 km/s. Earth

Direct Detection of Dark Matter Before Dark Matter Nucleus After Dark Matter Nucleus

Direct Detection of Dark Matter Before Look for kev energy Dark Matter Nucleus nuclear recoils. Spectrum from 8 GeV DM After Dark Matter Nucleus

Backgrounds to Direct Searches Many potential backgrounds from e.g. radioactivity in the shielding material. These limit the sensitivity of experiments, but can in principle be controlled.

Solar neutrino backgrounds Not to scale Dark Mountain Matter 1.5 km Direct Detection Experiment

Solar neutrino backgrounds Not to scale Dark Mountain Matter Solar Neutrinos The solar neutrino background is small but irreducible. 1.5 km Direct Detection Experiment

Solar neutrino backgrounds Solar neutrinos form an irreducible background to future light Dark Matter searches. ] -1 Event rate [(ton.year.kev) 5 10 2 10 10 8 10 2-45 2-1 Similar spectra for light DM and neutrinos WIMP signal: m = 6 GeV/c, Total CNS background Weak neutrino-electron Neutrino magnetic moment: Neutrino magnetic moment: -n = 4.4x10 = 3.2x10 = 1x10-11 -14 b b cm -4 10-3 10-2 10-1 10 1 10 10 Recoil energy [kev] 2 J. Billard, L. Strigari, and E. Figueroa-Feliciano, Phys.Rev. D89 (2014) 023524, [arxiv:1307.5458]

Solar neutrino backgrounds Solar neutrinos form an irreducible background to future light Dark Matter searches. ] -1 Event rate [(ton.year.kev) 5 10 2 10 10 8 10 2-45 2-1 Similar spectra for light DM and neutrinos WIMP signal: m = 6 GeV/c, Total CNS background Weak neutrino-electron Neutrino magnetic moment: Neutrino magnetic moment: -n = 4.4x10 = 3.2x10 = 1x10-11 -14 b b cm Particularly bad for light DM (m < 10 GeV) -4 10-3 10-2 10-1 10 1 10 10 Recoil energy [kev] 2 J. Billard, L. Strigari, and E. Figueroa-Feliciano, Phys.Rev. D89 (2014) 023524, [arxiv:1307.5458]

Solar neutrino backgrounds Exclusion power increases only slowly for 6 GeV DM due to this background, assuming a 10T low-threshold xenon detector.

Solar neutrino backgrounds Exclusion power increases only slowly for 6 GeV DM due to this background, assuming a 10T low-threshold xenon detector. Neutrino floor Sensitivity increases only slowly here due to systematic uncertainties.

Systematic uncertainties => Floor Dark Matter + Neutrinos Neutrinos only shaded region = Systematic uncertainty on neutrino flux Neutrino floor

Time variation of DM and neutrinos The solar neutrino and DM rates vary differently over the year. Use this as an additional discrimination parameter. Solar neutrinos Dark Matter

Time variation of DM and neutrinos The solar neutrino and DM rates vary differently over the year. Use this as an additional discrimination parameter. Solar neutrinos Dark Matter DM Flow Sun Earth

Time variation of DM and neutrinos The combined signal is a new cosine with a different phase and amplitude. Use this to look for a DM signal.

Example: with and without timing Dark Matter + Neutrinos Neutrinos only shaded region = Systematic uncertainty on neutrino flux

Example: with and without timing Dark Matter + Neutrinos Neutrinos only Can use timing information to separate a DM signal from the neutrino background. shaded region = Systematic uncertainty on neutrino flux

Effect of using time information The neutrino floor from systematic uncertainties is largely overcome using timing information. However Poisson limitation always remains.

Summary of Neutrino Backgrounds Neutrinos form an irreducible background to future direct searches. The spectrum from solar neutrinos is similar to light DM, resulting in a `neutrino floor The different time-dependence of the DM and solar neutrino signals can be used to overcome this floor. This can also be done with directionality (PRD 90 (2014) 5, 055018 and arxiv:1505.08061) or combining multiple experiments (PRD 90 (2014) 8, 083510). Jonathan Davis jonathan.h.m.davis@gmail.com