Direct detection of light dark matter. Joachim Kopp. IDM 2012, Chicago. Fermilab. Joachim Kopp Direct detection of light dark matter 1

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1 Direct detection of light dark matter Joachim Kopp IDM 2012, Chicago Fermilab Joachim Kopp Direct detection of light dark matter 1

2 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 2

3 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 3

4 Hints for light dark matter On the Earth... WIMPnucleon cross section Σ SI cm CDMS Xe 10 low thr. Limits : Countours: 90, 3Σ Plot based on JK Schwetz Zupan DAMA q ± 10 Xe v km s v esc 550 km s CoGeNT no surface BG CoGeNT small surface BG CoGeNT large surface BG CRESST WIMP mass m Χ GeV Several intriguing direct detection signals But severe tension with null results Joachim Kopp Direct detection of light dark matter 4

5 Hints for light dark matter On the Earth... WIMPnucleon cross section Σ SI cm CDMS Xe 10 low thr. Limits : Countours: 90, 3Σ Plot based on JK Schwetz Zupan DAMA q ± 10 Xe v km s v esc 550 km s CoGeNT no surface BG CoGeNT small surface BG CoGeNT large surface BG CRESST WIMP mass m Χ GeV Several intriguing direct detection signals But severe tension with null results... and in the skies An tentative γ ray excess from the Galactic Center Hooper Goodenough , , Morphology point source Radio filaments Linden Hooper Yusef-Zadeh Isotropic radio background Hooper Belikov Jeltema Linden Profumo Slatyer Joachim Kopp Direct detection of light dark matter 4

6 Theoretical motivation for light DM Conventional DM paradigm: DM has electroweak scale mass, weak scale couplings Thermal production The WIMP Miracle But note: Thermal production also possible for lighter DM Joachim Kopp Direct detection of light dark matter 5

Theoretical motivation for light DM Conventional DM paradigm: DM has electroweak scale mass, weak scale couplings Thermal production The WIMP Miracle But note: Thermal production also possible for

7 Theoretical motivation for light DM Conventional DM paradigm: DM has electroweak scale mass, weak scale couplings Thermal production The WIMP Miracle But note: Thermal production also possible for lighter DM An interesting alternative: Asymmetric dark matter Based on the observation that ΩDM 5 Ω baryon Suggests related production mechanisms Baryon abundance determined by matter antimatter asymmetry If DM carries baryon number and m DM 10m p, the observed ΩDM could be explained. Many model-building and phenomenology papers related to this idea: Kaplan Luty Zurek , Cai Luty Kaplan , Frandsen Sarkar Schmidt-Hober , Frandsen Sarkar , Feldstein Fitzpatrick , An Chen Mohapatra Nussinov Zhang , Cohen Phalen Pierce Zurek , Shelton Zurek , Haba Matsumoto , Davoudiasl Morrissey Sigurdson Tulin , Buckley Randall , Chun , Gu Lindner Sarkar Zhang , Blennow Dasgupta Fernandez-Martinez Rius , McDonald , Hall March-Russell West , Allahverdi Dutta Sinha , Dutta Kumar , Kouvaris Tinyakov , Falkowski Ruderman Volansky , Graesser Shoemaker Vecchi , McDermott Yu Zurek , Kouvaris Tinyakov , Buckley , Iminniyaz Drees Chen , Bell Petraki Shoemaker Volkas , Chang Goodenough , Cheung Zurek , Del Nobile Kouvaris Sannino , Masina Sannino , March-Russell McCullough , Davoudiasl Morrissey Sigurdson Tulin , Profumo Ubaldi , Cui Randall Shuve , Graesser Shoemaker Vecchi , Arina Sahu , Kane Shao Watson Yu , Buckley Profumo , Lewis Pica Sannino , Cirelli Panci Servant Zaharijas , Zentner Hearin , Lin Yu Zurek , Cui Randall Shuve , Kamada Yamaguchi , Tulin Yu Zurek , Walker , Davoudiasl Mohapatra , March-Russell Unwin West , Fan Yang Chang , Ellwanger Mitropoulos , Masina Panci Sannino , Okada Seto , Blennov Fernandez-Martinez Mena Redondo Serra ,... Joachim Kopp Direct detection of light dark matter 5

8 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 6

instance CCDs (DAMIC) DAMIC collaboration 1105.5191 Change the electrode geometry Point-contact detectors (CoGeNT) Luke Goulding.

9 Semiconductor detectors Binding energy of electrons in semiconductor detectors is very small (3 ev in Ge) Already a very feeble nuclear recoil leads to excitation Practical limitation: Electronic noise Possible solution: Reduce capacitance of the device Make them smaller for instance CCDs (DAMIC) DAMIC collaboration Change the electrode geometry Point-contact detectors (CoGeNT) Luke Goulding. Madden Pehl IEEE Trans. Nucl. Sci. 36 (1989) 926 Barbeau Collar Tench nucl-ex/ CoGeNT Super-CDMS Joachim Kopp Direct detection of light dark matter 7

10 Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Joachim Kopp Direct detection of light dark matter 8

11 Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Actual experimental energy threshold depends on kinematics: Threshold energy for WIMP nucleus scattering depends on Leff Difficult to measure (requires experiments with low-e neutrons) Difficult to calculate (interactions of primary recoil nucleus with other Xe atoms requires complicated many-body dynamics) Brenot et al. Phys. Rev. A 11 (1975) 1245; Ovchinnikov et al. Phys. Rept. 389 (2004) 119 Primary recoil ion hits Xe atom at rest Outer electrons rearrange themselves under the influence of both nuclei. Some of them may end up in excited or unbound states Joachim Kopp Direct detection of light dark matter 8

12 Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Actual experimental energy threshold depends on kinematics: Threshold energy for WIMP nucleus scattering depends on Leff Difficult to measure (requires experiments with low-e neutrons) Difficult to calculate (interactions of primary recoil nucleus with other Xe atoms requires complicated many-body dynamics) Brenot et al. Phys. Rev. A 11 (1975) 1245; Ovchinnikov et al. Phys. Rept. 389 (2004) 119 σn [cm 2 ] This work Ref. [11] Ref. [12] Ref. [26] Ref. [26] [GeV] m χ DAMA CoGeNT Xenon Joachim Kopp Direct detection of light dark matter 8

13 Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Actual experimental energy threshold depends on kinematics: Threshold energy for WIMP nucleus scattering depends on Leff Difficult to measure (requires experiments with low-e neutrons) Difficult to calculate (interactions of primary recoil nucleus with other Xe atoms requires complicated many-body dynamics) Brenot et al. Phys. Rev. A 11 (1975) 1245; Ovchinnikov et al. Phys. Rept. 389 (2004) 119 WIMP electron scattering very inefficient for O(100 GeV) dark matter JK Niro Schwetz Zupan Joachim Kopp Direct detection of light dark matter 8

14 Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Actual experimental energy threshold depends on kinematics: Threshold energy for WIMP nucleus scattering depends on Leff Difficult to measure (requires experiments with low-e neutrons) Difficult to calculate (interactions of primary recoil nucleus with other Xe atoms requires complicated many-body dynamics) Brenot et al. Phys. Rev. A 11 (1975) 1245; Ovchinnikov et al. Phys. Rept. 389 (2004) 119 WIMP electron scattering very inefficient for O(100 GeV) dark matter JK Niro Schwetz Zupan but an ideal process for MeV GeV DM Essig Mardon Volansky , Essig Manalaysay Mardon Sorensen Volansky Σe cm Hidden Photon models Excluded by XENON10 data 1 electron 2 electrons 3 electrons Dark Matter Mass MeV Joachim Kopp Direct detection of light dark matter 8

15 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 9

16 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 10

17 Material-dependent scattering cross sections How can the tension in the global data set when interpreted in terms of dark matter scattering be resolved? WIMPnucleon cross section Σ SI cm CDMS Xe 10 low thr. DAMA q ± 10 Limits : Countours: 90, 3Σ Xe v km s 550 km s v esc CoGeNT no surface BG CoGeNT small surface BG CoGeNT large surface BG CRESST WIMP mass m Χ GeV Plot based on JK Schwetz Zupan Joachim Kopp Direct detection of light dark matter 11

18 Material-dependent scattering cross sections How can the tension in the global data set when interpreted in terms of dark matter scattering be resolved? Isospin-violating DM Feng Kumar Marfatia Sanford Different couplings to protons and neutrons switch off xenon A 2 eff / A Na Si / Ca / O Ge Xe I W f n / f p Plot: JK Schwetz Zupan Joachim Kopp Direct detection of light dark matter 11

19 Material-dependent scattering cross sections How can the tension in the global data set when interpreted in terms of dark matter scattering be resolved? Isospin-violating DM Feng Kumar Marfatia Sanford Different couplings to protons and neutrons switch off xenon WIMPnucleon cross section Σeffcm CRESSTII DAMA mχ GeV IVDM, fn fp 0.7 Limits: 90 Contours: 90, 3Σ KIMS CRESST comm. run CDMS lowthr CDMSSi Xenon100 CDMS v0 220 kms, vesc 550 kms Plot: JK Schwetz Zupan Joachim Kopp Direct detection of light dark matter 11

20 Material-dependent scattering cross sections How can the tension in the global data set when interpreted in terms of dark matter scattering be resolved? Isospin-violating DM Feng Kumar Marfatia Sanford Different couplings to protons and neutrons switch off xenon Inelastic DM Tucker-Smith Weiner hep-ph/ Inelastic scattering prefers heavy targets (CRESST!) WIMPnucleon cross section Σeffcm CRESSTII DAMA IVDM, fn fp 0.7 Limits: 90 Contours: 90, 3Σ KIMS CRESST comm. run CDMS lowthr CDMSSi Xenon100 CDMS WIMPnucleon cross section ΣSIcm CRESST comm. run Xenon100 CRESSTII KIMS idm, 90keV Limits: 90 Contours: 90, 3Σ DAMA v0 220 kms, vesc 550 kms mχ GeV v0 220 kms, vesc 550 kms mχ GeV Plot: JK Schwetz Zupan Plot: JK Schwetz Zupan Joachim Kopp Direct detection of light dark matter 11

21 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 12

22 Dependence on the WIMP velocity distribution Conventional assumption: f (v) ( exp [ v 2 /v 2 0 ] exp [ v 2 esc /v 2 0 ] ) Θ(v esc v) However, N-body simulations predict deviations from this simple form v 2 v 2 f(v) fv Via Lactea vesc ~ 550 km/s v kms 5.00 Lisanti Strigari Wacker Wechsler GHALO vesc ~ 433 km/s Joachim Kopp Direct detection of light dark matter 13 Also: Streams and debris flow Lisanti Spergel , Kuhlen Lisanti Spergel v fv

23 Dependence on the WIMP velocity distribution standard f p f n 1 v kms v esc 500 kms q Na 0.3 Χ , 50.4 Σ SI in cm 2 DAMA CR C Cl F Xe Xe Si 14 M DM in GeV Si Xe Ge Farina Pappadopulo Strumia Volansky Joachim Kopp Direct detection of light dark matter 14

24 Dependence on the WIMP velocity distribution standard f p f n 1 v kms v esc 600 kms q Na 0.3 Χ , 73.2 Σ SI in cm 2 DAMA CR C Cl F Xe SiGe Si M DM in GeV Xe Farina Pappadopulo Strumia Volansky Joachim Kopp Direct detection of light dark matter 14

25 Dependence on the WIMP velocity distribution standard f p f n 1 v kms v esc 500 kms q Na 0.3 Χ , 72.0 Σ SI in cm 2 DAMA CR C Cl F Xe Xe Ge Si Si M DM in GeV Xe Farina Pappadopulo Strumia Volansky Joachim Kopp Direct detection of light dark matter 14

26 Dependence on the WIMP velocity distribution Σ SI in cm CR k 3 f p f n 1 v kms v esc 500 kms q Na 0.3 Χ , 72.3 DAMA C Cl F Xe 100 Xe M DM in GeV Si Ge Xe 10 Farina Pappadopulo Strumia Volansky Joachim Kopp Direct detection of light dark matter 14

27 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 15

28 Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected ) -R Winter )/(2R (R Average Summer Xenon Argon 10 ton*year Xenon 50 ton*year Argon Mass (GeV) Arisaka et al Joachim Kopp Direct detection of light dark matter 16

29 Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner and JK Schwetz Zupan Events kev kg day kev SI scattering days since kev days since kev days since kev days since kev days since Data points: CoGeNT, (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + best fit) for spin-independent scattering Extra surface BG = 0 kev 1 day 1 exp ( E/0.3keV ) (signal fraction in kev bin = 73%) Joachim Kopp Direct detection of light dark matter 16

30 Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner and JK Schwetz Zupan Events kev kg day kev SI scattering days since kev days since kev days since kev days since kev days since Data points: CoGeNT, (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + best fit) for spin-independent scattering Extra surface BG = 12 kev 1 day 1 exp ( E/0.3keV ) (signal fraction in kev bin = 46%) Joachim Kopp Direct detection of light dark matter 16

31 Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner and JK Schwetz Zupan Events kev kg day kev SI scattering days since kev days since kev days since kev days since kev days since Data points: CoGeNT, (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + best fit) for spin-independent scattering Extra surface BG = 24 kev 1 day 1 exp ( E/0.3keV ) (signal fraction in kev bin = 30%) Joachim Kopp Direct detection of light dark matter 16

32 Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner and JK Schwetz Zupan Events kev kg day kev SI scattering days since kev days since kev days since kev days since kev days since Data points: CoGeNT, (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + best fit) for spin-independent scattering When surface backgrounds are accounted for, reduced modulation in CoGeNT would make the data more consistent with a WIMP hypothesis Joachim Kopp Direct detection of light dark matter 16

33 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 17

34 Neutrinos as WIMP impostors Solar neutrinos are a well-known background to future direct DM searches: see e.g. Gütlein et al. arxiv: dσ SM (νn νn) = G2 F m NF 2 (E r ) [ de r 2πEν 2 A 2 Eν 2 + 2AZ (2Eν 2 (sw 2 1) E r m N sw) 2 ] + 4Z 2 (Eν 2 + sw(2e 4 ν 2 + Er 2 E r (2E ν + m N )) + sw(e 2 r m N 2Eν 2 )), countsnakevyear pp 7 Be 13 N 15 O pep CoGeNT SM total rate Components 17 F electron recoil DAMA 8 B hep Erec kev XENON100 e Borexino countstonkevyear pp 7 Be 13 N 15 O pep hep Nuclear recoil Ge 8 B 17 F SM total rate Components Erec kev CoGeNT CDMSII Plots from Harnik JK Machado Joachim Kopp Direct detection of light dark matter 18

35 Neutrinos as WIMP impostors Solar neutrinos are a well-known background to future direct DM searches: see e.g. Gütlein et al. arxiv: dσ SM (νn νn) = G2 F m NF 2 (E r ) [ de r 2πEν 2 A 2 Eν 2 + 2AZ (2Eν 2 (sw 2 1) E r m N sw) 2 ] + 4Z 2 (Eν 2 + sw(2e 4 ν 2 + Er 2 E r (2E ν + m N )) + sw(e 2 r m N 2Eν 2 )), SM signal will only become sizeable in multi-ton detectors But: New physics can enhance the rate New ν physics can be confused with a dark matter signal DM detectors can search for new physics in the ν sector Joachim Kopp Direct detection of light dark matter 18

36 Enhanced neutrino scattering from BSM physics Harnik JK Machado countsnakeveeyear B C A CoGeNT Standard model DAMA D Line M A g eg Ν A Μ Ν Μ B B 10 kev C 50 kev D 250 kev rec ee XENON100 e Borexino A: ν magnetic moment B, C, D: kinetically mixed A + sterile ν s: L 1 4 F µνf µν 1 4 FµνF µν 1 2 ɛf µνf µν + ν si / ν s + g ν sγ µ ν sa µ (ν L ) c m νl ν L (ν s) c m νs ν s (ν L ) c m mix ν s Enhanced scattering at low E r for light A Negligible compared to SM scattering at energies probed in dedicated neutrino experiments Various mechanisms for daily and annual modulation Pospelov , Harnik JK Machado Joachim Kopp Direct detection of light dark matter 19

37 Enhanced neutrino scattering from BSM physics countsnakeveeyear B C A CoGeNT DAMA D rec ee XENON100 e Harnik JK Machado Nuclear recoil Ge 10 5 Standard model 10 1 Line M A g eg Ν Line M Borexino A g Ng Ν sin 2 Θ A Μ Ν Μ B 10 0 A Μ Ν Μ B active 10 7 B 10 kev B 100 MeV active C 50 kev C 100 MeV D 250 kev D 10 MeV countstonkevnryear Standard model A E rec kev nr D B C CoGeNT CDMSII A: ν magnetic moment A: ν magnetic moment B, C, D: kinetically mixed A + sterile ν s B: U(1) B L boson C: kinetically mixed U(1) + sterile ν D: U(1) B + sterile ν charged under U(1) B Pospelov , Pospelov Pradler Enhanced scattering at low E r for light A Negligible compared to SM scattering at energies probed in dedicated neutrino experiments Various mechanisms for daily and annual modulation Pospelov , Harnik JK Machado Joachim Kopp Direct detection of light dark matter 19

38 Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 20

39 Summary and conclusions Several intriguing experimental hints for 10 GeV DM Theoretical motivation in asymmetric DM scenarios, but can be accomodated in many popular DM models Direct detection of light dark matter requires new experimental techniques Currently, data from different experiments contradict each other CoGeNT, DAMA, CRESST see unexplained signals Strong exclusion from Xenon-100, CDMS,... (under standard assumptions) Note: Reduced modulation removes tension within the CoGeNT data Ways out: Material-dependent scattering cross sections? (isospin-violating DM, inelastic DM) New physics in the neutrino sector can fake WIMP signals Joachim Kopp Direct detection of light dark matter 21

40 Thank you!

41 Bonus slides

42 Example: A model with a 4th neutrino Introduce a 4 th neutrino ν s and a light U(1) gauge boson A (hidden photon) Harnik JK Machado related model with gauged U(1) B first discussed by Pospelov see also Pospelov Pradler ν s charged under U(1) direct coupling to A SM particles couple to A only through kinetic mixing L 1 4 F µνf µν 1 4 F µνf µν 1 2 ɛf µνf µν + ν s i / ν s + g ν s γ µ ν s A µ (ν L ) c m νl ν L (ν s ) c m νs ν s (ν L ) c m mix ν s A small fraction of solar neutrinos can oscillate into ν s ν s scattering cross section in the detector given by dσ A (ν s e ν s e) ɛ 2 e 2 g 2 m e [ = 2E 2 de r 4πpν(M 2 A 2 + 2E r m e ) 2 ν + Er 2 2E r E ν E r m e mν 2 ] Joachim Kopp Direct detection of light dark matter 24

43 Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter. Joachim Kopp Direct detection of light dark matter 25

Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter.

44 Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter. Active sterile neutrino oscillations: For oscillation lengths 1 AU, sterile neutrino appearance depends on the time of year. Harnik JK Machado, arxiv: Joachim Kopp Direct detection of light dark matter 25

45 Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter. Active sterile neutrino oscillations: For oscillation lengths 1 AU, sterile neutrino appearance depends on the time of year. Sterile neutrino absorption: For strong ν s A couplings and not-too-weak A SM couplings, sterile neutrino cannot traverse the Earth. lower flux at night. And nights are longer in winter. Joachim Kopp Direct detection of light dark matter 25

46 Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter. Active sterile neutrino oscillations: For oscillation lengths 1 AU, sterile neutrino appearance depends on the time of year. Sterile neutrino absorption: For strong ν s A couplings and not-too-weak A SM couplings, sterile neutrino cannot traverse the Earth. lower flux at night. And nights are longer in winter. Earth matter effects: An MSW-type resonance can lead to modified flux of certain neutrino flavors at night. And nights are longer in winter. Joachim Kopp Direct detection of light dark matter 25

47 Hidden photons L 1 4 F µνf µν 1 4 F µνf µν 1 2 ɛf µνf µν + ν s i / ν s + g ν s γ µ ν s A µ Kinetic mixing Ε g2μ Atomic Physics Atomic Physics g Ν 2 sin 2 2Θ g Ν 2 sin 2 2Θ 10 4 CMB Kinetically Mixed Gauge Boson CMB LSW Fixed target Dark Photon Mass M A' GeV CAST Borexino in models with U1'charged sterile Ν SunGlobular Clusters, energy loss via Ν s in models with 10 kev sterile neutrinos A' capture in Sun partly allowed Sun Globular Clusters g2e SN1987A Constraints from Jaeckel Ringwald , Redondo , Bjorken Essig Schuster Toro , Dent Ferrer Krauss , Harnik JK Machado Joachim Kopp Direct detection of light dark matter 26

light dm in the light of cresst-ii

light dm in the light of cresst-ii Jure Zupan U. of Cincinnati based on T. Schwetz, JZ 1106.6241; J. Kopp, T. Schwetz, JZ 1110.2721 1 the question CoGeNT, DAMA, CRESST claim signals Is it (can it be) dark