Direct detection of light Zhengkang Kevin Zhang dark matter with - PowerPoint PPT Presentation

Direct detection of light Zhengkang “Kevin” Zhang dark matter with magnons UC Berkeley Based on: Tanner Trickle, ZZ, Kathryn Zurek, arXiv: 1905.13744. Fermilab/KICP, Jun. 2019

Roadmap Collective excitations as a path forward for light DM Kinematic matching in Phonons : detect spin-independent interactions DM direct detection Kinematics Dynamics MeV m χ = 100 keV Magnons : detect spin-dependent interactions l i keV o electron excitations in c e r semiconductors r a e Δ E l c u n eV collective excitations: phonons, magnons meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 2 Fermilab/KICP, Jun. 2019

Kinematic matching q 2 1 ( m χ v ) 2 − ( m χ v − q ) 2 � � ∆ E = ≤ vq − 2 m χ 2 m χ MeV incoming DM m χ = 100 GeV velocity v ~10 -3 nuclear recoil keV momentum transfer q energy transfer 𝛦 E Δ E eV meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 3 Fermilab/KICP, Jun. 2019

Kinematic matching q 2 1 ( m χ v ) 2 − ( m χ v − q ) 2 � � ∆ E = ≤ vq − 2 m χ 2 m χ MeV m χ = 100 MeV nuclear recoil keV Δ E eV meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 4 Fermilab/KICP, Jun. 2019

Kinematic matching q 2 1 ( m χ v ) 2 − ( m χ v − q ) 2 � � ∆ E = ≤ vq − 2 m χ 2 m χ MeV Band gap: O(eV). m χ = 100 MeV nuclear recoil keV electron excitations in semiconductors Δ E eV Essig, Mardon, Volansky, 1108.5383. Graham, Kaplan, Rajendran, Walters, 1203.2531. Lee, Lisanti, Mishra-Sharma, Safdi, 1508.07361. Essig, Fernandez-Serra, Mardon, Soto, Volansky, Yu, 1509.01598. Derenzo, Essig, Massari, Soto, Yu, 1607.01009. meV See talk by T. Yu. eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 5 Fermilab/KICP, Jun. 2019

Kinematic matching q 2 1 ( m χ v ) 2 − ( m χ v − q ) 2 � � ∆ E = ≤ vq − 2 m χ 2 m χ MeV m χ = 100 keV nuclear recoil keV electron excitations in semiconductors Δ E eV meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 6 Fermilab/KICP, Jun. 2019

Kinematic matching q 2 1 ( m χ v ) 2 − ( m χ v − q ) 2 � � ∆ E = ≤ vq − 2 m χ 2 m χ MeV Phonons/magnons in crystals m χ = 100 keV with energies up to O(100meV). 100 nuclear recoil 90 keV 80 electron excitations 70 in semiconductors 60 50 Δ E 40 30 20 10 eV collective excitations: Knapen, Lin, Pyle, Zurek, 1712.06598. phonons, magnons Griffin, Knapen, Lin, Zurek, 1807.10291. Trickle, ZZ, Zurek, 1905.13744. Griffin, Inzani, Trickle, ZZ, Zurek, to appear. See talks by T. Lin, S. Griffin. meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 7 Fermilab/KICP, Jun. 2019

Phonons in crystals: a brief recap See talks by T. Lin, S. Griffin. Coupled quantum harmonic oscillators. ❖ Diagonalize the Hamiltonian => canonical modes — phonons (quanta ❖ of collective oscillation patterns). atom displacements phonon creation/annihilation operators phonon mode labels phonon polarization vectors Zhengkang “Kevin” Zhang (UC Berkeley) 8 Fermilab/KICP, Jun. 2019

Phonons in crystals: a brief recap See talks by T. Lin, S. Griffin. Single phonon excitation from DM ❖ scattering (dark photon mediator case): phonon mode labels 1 1  eg χ X Q j e i q · x lj | 0 i M ν , k ( q ) = q 2 h ⌫ , k | N Ω ✏ ∞ l,j position operators create phonons Griffin, Knapen, Lin, Zurek, 1807.10291. Zhengkang “Kevin” Zhang (UC Berkeley) 9 Fermilab/KICP, Jun. 2019

Roadmap Collective excitations as a path forward for light DM Kinematic matching in Phonons : detect spin-independent interactions DM direct detection Kinematics MeV m χ = 100 keV l i keV o electron excitations in c e r semiconductors r a e Δ E l c u n eV collective excitations: phonons, magnons meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 10 Fermilab/KICP, Jun. 2019

Roadmap Collective excitations as a path forward for light DM Kinematic matching in Phonons : detect spin-independent interactions DM direct detection Kinematics Dynamics MeV m χ = 100 keV How does the DM couple to l i keV o electron excitations in c e r semiconductors r Standard Model particles? a e Δ E l c u n eV collective excitations: phonons, magnons meV eV keV MeV GeV q Zhengkang “Kevin” Zhang (UC Berkeley) 11 Fermilab/KICP, Jun. 2019

DM coupling to electron spin In the Standard Model, the neutron is electrically neutral. Its leading ❖ interaction with the photon is via a magnetic dipole moment. Something similar can happen in the dark sector. The DM may be ❖ neutral under the dark photon, but interacts via a multipole moment. In these scenarios, DM couples to the electron spin at low energy: ❖ Such couplings can also arise in scalar mediator models. ❖ Zhengkang “Kevin” Zhang (UC Berkeley) 12 Fermilab/KICP, Jun. 2019

Roadmap Phonons : detect spin-independent interactions Dynamics Magnons : detect spin-dependent interactions Zhengkang “Kevin” Zhang (UC Berkeley) 13 Fermilab/KICP, Jun. 2019

Magnons: what they are and how they couple to DM Crystal lattice sites occupied by effective spins (from electrons of magnetic ions.) ❖ E xchange couplings between neighboring spins => ordered ground state . ❖ Excitations about such a ground state are magnons . ❖ Zhengkang “Kevin” Zhang (UC Berkeley) 14 Fermilab/KICP, Jun. 2019

Magnons: what they are and how they couple to DM Technically, we need to expand the spins in terms of bosonic creation/annihilation ❖ operators via the Holstein-Primakoff transformation… where global coordinates local coordinates (ground state spin points in +z direction) … and then diagonalize the Hamiltonian via a Bogoliubov transformation… ❖ canonical magnon modes (quanta of collective precession patterns) Zhengkang “Kevin” Zhang (UC Berkeley) 15 Fermilab/KICP, Jun. 2019

Magnons: what they are and how they couple to DM Technically, we need to expand the spins in terms of bosonic creation/annihilation ❖ operators via the Holstein-Primakoff transformation… where global coordinates local coordinates (ground state spin points in +z direction) … and then diagonalize the Hamiltonian via a Bogoliubov transformation… ❖ canonical magnon modes DM-spin coupling => DM-magnon coupling. ❖ (quanta of collective precession patterns) 1 M s i s f N Ω h s f | ˆ ˆ X lj e i q · x lj | 0 i ) ν , k ( q ) = O α χ ( q ) | s i ih ν , k | S α lj spin operators create magnons (cf. position operators create phonons) Zhengkang “Kevin” Zhang (UC Berkeley) 16 Fermilab/KICP, Jun. 2019

Projected reach We consider a yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) target. ❖ 20 magnetic ions Fe 3+ (spin 5/2) in the unit cell => 20 magnon branches. ❖ Anti-ferromagnetic exchange couplings. Ground state: 12 up, 8 down. ❖ 100 90 80 70 60 50 40 30 20 10 Magnon dispersion calculated by including up to 3rd nearest neighbor exchange couplings taken from: Cherepanov, Kolokolov, L’vov, Physics Reports 229, 81 (1993). Zhengkang “Kevin” Zhang (UC Berkeley) 17 Fermilab/KICP, Jun. 2019

Projected reach We consider a yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) target. ❖ Dark photon mediator (unconstrained by astro/cosmo): ❖ Magnetic dipole DM Anapole DM Ω χ Ω 10 - 33 10 - 31 10 - 32 10 - 34 10 - 33 10 - 35 10 - 34 10 - 36 10 - 35 π χ 10 - 37 g χ g e m χ / Λ χ = 10 - 8 10 meV 10 - 36 10 meV g χ 40 meV g e 10 - 38 10 - 37 m χ σ e [ cm 2 ] σ e [ cm 2 ] ] 2 / Λ χ 40 meV 2 = 10 - 5 ω 10 - 39 10 - 38 σ [ 10 - 9 10 - 39 10 - 40 ω min = 1 meV 1 10 - 40 0 - 6 10 - 41 ω min = 1 meV χ 10 - 10 10 - 41 1 0 - 7 10 - 42 10 - 42 10 - 43 10 - 43 10 - 44 10 - 44 10 - 45 10 - 45 10 - 2 10 - 1 1 10 10 - 2 10 - 1 1 10 m χ [ MeV ] m χ [ MeV ] χ Projection assumes 3 signal events/kg/yr. Zhengkang “Kevin” Zhang (UC Berkeley) 18 Fermilab/KICP, Jun. 2019

Projected reach We consider a yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) target. ❖ Scalar mediator (impose white dwarf cooling constraint, ❖ consider SIDM subcomponent): Pseudo - mediated DM ( Ω χ / Ω DM = 0.05 ) 10 - 39 10 - 40 g χ = 4 π 4 10 - 41 0 χ m 1 0 χ Λ e m χ χ V e σ e [ cm 2 ] V χ Λ χ ω 10 - 42 m i n σ σ ω = 1 m g χ = 1 10 - 43 ω e V 10 - 44 10 - 45 10 10 - 2 10 - 1 1 10 m χ [ MeV ] χ χ Zhengkang “Kevin” Zhang (UC Berkeley) 19 Fermilab/KICP, Jun. 2019

Summary Collective excitations in condensed matter systems offer promising detection ❖ paths for light DM due to kinematic matching . There is also a dynamics aspect of direct detection. Different excitations can ❖ be sensitive to different DM interactions. Previously phonons have been demonstrated to have capability of probing ❖ interesting DM scenarios with spin-independent interactions. We have shown that magnons (collective spin excitations) can be used to ❖ probe spin-dependent DM interactions, complementary to phonons. Next steps: ❖ Detection schemes. ❖ DM absorption. ❖ Other types of target responses? ❖ Zhengkang “Kevin” Zhang (UC Berkeley) 20 Fermilab/KICP, Jun. 2019

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