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Majorana Neutrino Spectroscopy: Measuring Relic Neutrinos

This paper explores the detection of Majorana neutrinos through atomic processes and discusses the measurement of absolute mass scale and the possibility of detecting relic neutrinos. It also examines the significance of discovering Majorana neutrinos and their implications for lepton number violation and leptogenesis. The merits and demerits of atomic processes in Majorana detection are examined, along with the unique signatures of Majorana neutrinos and the potential for direct tests of their nature. The paper concludes by proposing experimental strategies for discovering relic neutrinos.

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Majorana Neutrino Spectroscopy: Measuring Relic Neutrinos

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  1. Majorana neutrino spectroscopy and measuring relic neutrinoM. Yoshimura hep-ph/0611362 • Why atoms ? • Another or perhaps a unique way of Majorana detection • Measurement of absolute mass scale • Possibility of detecting relic neutrino hep-ph/0703019

  2. Significance of discovering Majorana neutrino • Neutral fermions follow economic Majorana eq or the same Dirac eq as charged ? • Leading to lepton number violation and lepto-genesis particle = anti-particle missing partner for leptogenesis • Contributing to better understanding of seesaw mechanism and GUT

  3. M vs D

  4. Merits and demerits of atomic process • Infinitely many small energies • Small pair emission rate • How to enhance is crucial resonance by energy input strong field

  5. Majorana ｖｓ　Dirac equations:chirally projected solutions

  6. Unique signature of Majorana = interference of identical fermions • Effective only for pair emission • Appear only (ii) threshold; proportional to m_i^2 • Can be positive or negative • Direct test of Majorana nature cf LV in

  7. 2 promissing atomic processes • Low level metastable atoms laser irradiated • Rydberg atoms microwave irradiated (not discussed here)

  8. Neutrino pair emission from laser irradiated metastable state

  9. Rough estimate of rate

  10. Refinement

  11. Majorana vs Dirac 6 channels available

  12. Numerical estimate w.Y. Okabayashi • Input angles and masses: case of normal hierarchy

  13. Red Blue M : ~4% M : ~2% M : ~9% M : ~1% 500(meV) 700(meV) 300(meV) D : ~3% D : ~1% D : ~7% 900(meV) D : ~0.8% Mass varied Effect

  14. Large mass effects

  15. Mixing angle varied Red Blue M : ~3% M : ~2% M : ~8% M : ~1% 500(meV) 700(meV) 300(meV) D : ~2% D : ~1% D : ~6% 900(meV) D : ~0.8% Finite masseffect

  16. Theta_12 effect

  17. Case of inverted mass hierarchy ① ② ① ③ ④ ② ③ ④ ⑤ ⑥ ⑤ ⑥

  18. Observability of relic neutrino w. T. Takahashihep-ph/0703019 • Pauli blocking effect

  19. Crucial question how large the “threshold ” region

  20. Magnitude of Pauli blocking

  21. m_1 dependence for standard 1.9 K For m_1 > 5 meV, the “threshold” region is narrow For m_1 < 1 meV, the “threshold” region is wide

  22. Temperature measurement possible ? For m_1 < 1meV, temperature measurement is not difficult

  23. 12 threshold Smaller effect with a larger rate

  24. Early universe probed by relic neutrino • Decoupling temperature • Early universe after neutrino decoupling and before e^+ annihilation • Large lepton asymmetry • Constraint on sterile neutrino • Surprizes ?

  25. Measuring the lepton asymmetry • Definitive test of leptogenesis • Extremely difficult, (12) threshold most promissing

  26. Experiments are not easy: a possible strategy • Discovery of atomic pair emission • Mass measurement • M/D distinction • Relic detection

  27. Level structure of candidate atom

  28. Summary • Discussed laser irradiated pair emission to determine the magnitude and the nature of neutrino masses • Identical particle effect of Majorana particles • Neutrino mass spectroscopy towards 1 meV range • Relic neutrino search

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