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Submitted on 7 Apr 2011
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Self-adjoint (a, b)-modules and hermitian forms
Piotr P. Karwasz
To cite this version:
✵✳✸✳ ❙❯■❚❊❙ ❉❊ ❏❖❘❉❆◆✲❍Ö▲❉❊❘ ❆❯❚❖✲❆❉❏❖■◆❚❊❙ ✶✶ ❖♥ ❝❤♦✐s✐t ❧❛ ❞é✜♥✐t✐♦♥ ❞❡ ❉✳ ❇❛r❧❡t ❞❡ ❞✉❛❧ E✝ ❞✬✉♥ ♣a, bq✲♠♦❞✉❧❡ E✱
q✉✐ ❛ ❧✬❛✈❛♥t❛❣❡ ❞❡ ♥❡ ♣❛s ❝❤❛♥❣❡r ❧❛ Crrbss✲str✉❝t✉r❡ ♥❛t✉r❡❧❧❡ s✉r E✝✳ ▲❡
❞✉❛❧ ❡st ❛✐♥s✐ ❧❡ Crrbss✲♠♦❞✉❧❡ HomCrrbss♣E, E0q✱ ♦ù E0 ❡st ❧❡ ♣a, bq✲♠♦❞✉❧❡
é❧é♠❡♥t❛✐r❡ ❞❡ r❛♥❣ 1 ❡♥❣❡♥❞ré ♣❛r ✉♥ é❧é♠❡♥t e0 q✉✐ ✈ér✐✜❡ ae0 ✏ 0✱ ❡t ❧❛
a✲str✉❝t✉r❡ s✉r E✝ ❡st ❞♦♥♥é❡ ♣❛r
♣aϕq♣xq ✏ a♣ϕ♣xqq ✁ ϕ♣axq ♣♦✉r t♦✉t ϕ P E✝ ❡t x P E✳
▲❛ ♥♦t✐♦♥ ❞❡ δ✲❞✉❛❧ ❞❡ ❇❡❧❣r❛❞❡ s❡r❛ ré❞✉✐t❡ à ❧❛ ♥♦t✐♦♥ ❞❡ ❞✉❛❧ à ❧✬❛✐❞❡ ❞✬✉♥ ❢♦♥❝t❡✉r ❞❡ ❝♦♥❥✉❣❛✐s♦♥ ˇ✱ q✉✐ é❝❤❛♥❣❡ ❧❡s s✐❣♥❡s ❞❡s ❛❝t✐♦♥s ❞❡ a ❡t b ✭a Ñ ✁a ❡t b Ñ ✁b✮✱ ❡t ❞✉ ❝♦♥❝❡♣t ❞❡ ♣r♦❞✉✐t t❡♥s♦r✐❡❧ ❞❡ ❞❡✉① ♣a, bq✲♠♦❞✲ ✉❧❡s E ❡t F ✱ q✉✐ ❢❛❝t♦r✐s❡ t♦✉t❡ ❛♣♣❧✐❝❛t✐♦♥ Crrbss✲❜✐❧✐♥é❛✐r❡
Φ : E✂ F Ñ G, ❞❛♥s ✉♥ tr♦✐s✐è♠❡ ♣a, bq✲♠♦❞✉❧❡ G s❛t✐s❢❛✐s❛♥t
a♣Φ♣x, yqq ✏ Φ♣ax, yq Φ♣x, ayq,
✷✷ ❈❍❆P❚❊❘ ✶✳ ❚❍❊❖❘❨ ❖❋ ♣A, Bq✲▼❖❉❯▲❊❙ ❊①❛♠♣❧❡ ✶✳✷✷ ✭❙✐♠♣❧❡ ♣a, bq✲♠♦❞✉❧❡ ♦❢ r❛♥❦ 2✮✳ ❚❤❡ ❡①❛♠♣❧❡ ♦❢ ♥♦♥ r❡❣✉❧❛r ♣a, bq✲♠♦❞✉❧❡ ❣✐✈❡♥ ❛t t❤❡ ❡♥❞ ♦❢ s✉❜s❡❝t✐♦♥ ✶✳✶✳✷ ✐s s✐♠♣❧❡✳ ▲❡t✱ ✐♥ ❢❛❝t✱ e1 ❛♥❞ e2 ❜❡ ✐ts ❣❡♥❡r❛t♦rs t❤❛t s❛t✐s❢② ae1 ✏ e2 ae2 ✏ be1. ❙✐♥❝❡ ✐t ❤❛s r❛♥❦ 2 ✐♥ ♦r❞❡r t♦ s❤♦✇ t❤❛t ✐t✬s s✐♠♣❧❡✱ ✐t ✐s ❡♥♦✉❣❤ t♦ s❤♦✇ t❤❛t ✐t ❞♦❡s♥✬t ❝♦♥t❛✐♥ ❛♥② ♥♦r♠❛❧ s✉❜✲♣a, bq✲♠♦❞✉❧❡ ♦❢ r❛♥❦ 1✳ ▲❡t ♣r♦❝❡❡❞ ❜② ❝♦♥tr❛❞✐❝t✐♦♥ ❛♥❞ s✉♣♣♦s❡ t❤❡r❡ ✐s ❛ ♥♦r♠❛❧ s✉❜✲♣a, bq✲♠♦❞✉❧❡ F ♦❢ r❛♥❦ 1 ❣❡♥❡r❛t❡❞ ❜② ❛♥ ❡❧❡♠❡♥t f P F ✳ ❇② ❡✈❡♥t✉❛❧❧② ♠✉❧t✐♣❧②✐♥❣ f ❜② ❛♥ ✐♥✈❡rt✐❜❧❡ ❡❧❡♠❡♥t ♦❢ Crrbss✱ ✇❡ ❝❛♥ ❛ss✉♠❡ ✐t ✐s ♦❢ t❤❡ ❢♦r♠ e1 S♣bqe2 ♦r S♣bqe1 e2✱ ✇✐t❤ S♣bq P Crrbss✳ ■♥ t❤❡ ✜rst ❝❛s❡ ✇❡ ❤❛✈❡ t♦ s♦❧✈❡ t❤❡ ❡q✉❛t✐♦♥✿
a♣e1 S♣bqe2q ✏ e2 S♣bqbe1 S✶♣bqb2e2 ✏ T ♣bq ♣e1 S♣bqe2q ,
❢♦r ❛♥ ✉♥❦♥♦✇♥ T ♣bq P Crrbss✳ ❈❧❡❛r❧② ✇❡ ♠✉st ❤❛✈❡ T ♣bq ✏ S♣bqb ❧♦♦❦✐♥❣ ❛t t❤❡ ❝♦❡✣❝✐❡♥ts ♦❢ e1✳ ❚❤❡r❡❢♦r❡ ❜② ✐❞❡♥t✐❢②✐♥❣ t❤❡ ❝♦❡✣❝✐❡♥ts ♦❢ e2 ♦♥ t❤❡ r✐❣❤t ❛♥❞ ❧❡❢t s✐❞❡ ♦❢ t❤❡ ❡q✉❛t✐♦♥✱ ✇❡ ♠✉st ❤❛✈❡✿ 1 S✶♣bqb2 ✏ S2♣bqb, ✇❤✐❝❤ ✐s ✐♠♣♦ss✐❜❧❡✱ s✐♥❝❡ t❤❡ r✐❣❤t s✐❞❡ ❧❛❝❦s ❛ ❝♦♥st❛♥t t❡r♠✳ ■♥ ❛ s✐♠✐❧❛r ♠❛♥♥❡r ✇❡ ♣r♦❝❡❡❞ ❢♦r t❤❡ ❝❛s❡ f ✏ S♣bqe1 e2✳ ❚❤❡ ❡q✉❛t✐♦♥
a♣S♣bqe1 e2q ✏ S♣bqe2 S✶♣bqb2e1 be1 ✏ T ♣bq ♣S♣bqe1 e2q ,
✷✹ ❈❍❆P❚❊❘ ✶✳ ❚❍❊❖❘❨ ❖❋ ♣A, Bq✲▼❖❉❯▲❊❙ ❘❡♠❛r❦ ✶✳✷✺✳ ■❢ E ✐s r❡❣✉❧❛r✱ t❤❡♥ t❤❡ s✉❜✲♣a, bq✲♠♦❞✉❧❡s ❛♥❞ q✉♦t✐❡♥ts ♦❢ t❤❡ ❝♦♠♣♦s✐t✐♦♥ s❡r✐❡s ❛r❡ ❛❧s♦ r❡❣✉❧❛r✳ ❲❡ ✐♥tr♦❞✉❝❡❞ ✐♥ ✶✳✷✶ ❛ ❝❧❛ss ♦❢ s✐♠♣❧❡ r❡❣✉❧❛r ♣a, bq✲♠♦❞✉❧❡s ♦❢ r❛♥❦ 1✳ ❚❤❡ ❢♦❧❧♦✇✐♥❣ ♣r♦♣♦s✐t✐♦♥✱ ❢♦r ✇❤✐❝❤ ✇❡ ❣✐✈❡ ❛ ❝♦♥❞❡♥s❡❞ ♣r♦♦❢ ✭❝❢✳ ❬❇❛r✾✸❪✮✱ s❤♦✇s ✉s t❤❛t t❤❡② ❛r❡ t❤❡ ♦♥❧② r❡❣✉❧❛r s✐♠♣❧❡ ♣a, bq✲♠♦❞✉❧❡s✳ Pr♦♣♦s✐t✐♦♥ ✶✳✷✻✳ ▲❡t E ❜❡ ❛ r❡❣✉❧❛r ♣a, bq✲♠♦❞✉❧❡✱ t❤❡♥ ✐t ❝♦♥t❛✐♥s ❛ ♥♦r✲ ♠❛❧ s✐♠♣❧❡ s✉❜✲♣a, bq✲♠♦❞✉❧❡ ♦❢ r❛♥❦ 1 ♦❢ t❤❡ ❢♦r♠ Eλ✳ Pr♦♦❢✳ ❲❡ ✇✐❧❧ r❡❞✉❝❡ ♦✉rs❡❧✈❡s t♦ t❤❡ ❝❛s❡ ♦❢ ❛ s✐♠♣❧❡✲♣♦❧❡ ♣a, bq✲♠♦❞✉❧❡✳ ❯s✐♥❣ t❤❡ r❡s✉❧t ❢r♦♠ ❧❡♠♠❛ ✶✳✶✷ ✇❡ ✜♥❞ ❛ s✐♠♣❧❡✲♣♦❧❡ ♣a, bq✲♠♦❞✉❧❡ E# t❤❛t ❝♦♥t❛✐♥s E ❛♥❞ s✉❝❤ t❤❛t E#④E ✐s ♦❢ ✜♥✐t❡ ❞✐♠❡♥s✐♦♥ ♦✈❡r C✳ ❙✉♣♣♦s❡ ♥♦✇ t❤❛t t❤❡r❡ ✐s ❛ ♥♦r♠❛❧ s✉❜✲♣a, bq✲♠♦❞✉❧❡ F ♦❢ E# ♦❢ r❛♥❦ 1 ❣❡♥❡r❛t❡❞ ❜② ❛♥ ❡❧❡♠❡♥t e ❛♥❞ ❧❡t λ P C s✉❝❤ t❤❛t ae ✏ λbe ✭s✐♥❝❡ F ♠✉st ❜❡ s✐♠♣❧❡✲♣♦❧❡✮✳ ❙✐♥❝❡ E#④E ✐s ♦❢ ✜♥✐t❡ ❞✐♠❡♥s✐♦♥ t❤❡r❡ ✐s ❛♥ n P N s✉❝❤ t❤❛t bneP E✳ ▲❡t n0 ❜❡ t❤❡ ♠✐♥✐♠❛❧ n s✉❝❤ t❤❛t bn0e P E ❲❡ ❛ss❡rt t❤❛t t❤❡ s✉❜✲ ♣a, bq✲♠♦❞✉❧❡ F✶ ♦❢ E ❣❡♥❡r❛t❡❞ ❜② bn0x ✐s ♥♦r♠❛❧ ❛♥❞ ✐s♦♠♦r♣❤✐❝ t♦ E λ n0 ❛s ❛♥ ♣a, bq✲♠♦❞✉❧❡✳ ■♥ ❢❛❝t s✐♥❝❡ ae ✏ λbe✱ ❜② ✉s✐♥❣ ✶✳✷ ✇❡ ♦❜t❛✐♥ a.♣bn0qe ✏ ♣λ n 0qb.bn0e✱ ✇❤✐❝❤ s❤♦✇s t❤❛t F✶ ✐s ✐s♦♠♦r♣❤✐❝ t♦ E λ n0✳ ❖♥ t❤❡ ♦t❤❡r s✐❞❡ F✶ ✐s ♥♦r♠❛❧ ✐♥ E✿ ✐❢ n 0 → 0 t❤❡ ♠✐♥✐♠❛❧✐t② ♦❢ t❤✐s ♥✉♠❜❡r ❣✉❛r❛♥t❡❡s ✉s t❤❛t bn0e❞♦❡s ♥♦t ❜❡❧♦♥❣ t♦ bE ✭♦t❤❡r✇✐s❡ bn0✁1eP E✮ ❛♥❞ t❤❡ ❝♦r♦❧❧❛r② ✶✳✶✽ ❣✐✈❡s ✉s t❤❡ ♥♦r♠❛❧✐t② ♦❢ F✶✳ ■❢✱ ❤♦✇❡✈❡r✱ n0 ✏ 0 ✇❡ ❤❛✈❡ ❜② ❤②♣♦t❤❡s✐s t❤❛t F✶ ✏ F ✐s ♥♦r♠❛❧ ✐♥ E#✱ ❤❡♥❝❡ ♥♦r♠❛❧ ✐♥ E✿ ✐❢ E#④F ✐s ❢r❡❡✱ s♦ ✐s ✐ts s✉❜✲Crrbss✲♠♦❞✉❧❡ E④F ✳ ❲❡ ❝❛♥ t❤❡r❡❢♦r❡ r❡❞✉❝❡ ♦✉rs❡❧✈❡s t♦ s❤♦✇ t❤❡ ♣r♦♣♦s✐t✐♦♥ ❢♦r ❛ s✐♠♣❧❡✲ ♣♦❧❡ ♣a, bq✲♠♦❞✉❧❡ E✱ ✇❤✐❝❤ ✇❡ ✇✐❧❧ ❞♦ ✐♥ t❤❡ ❢♦❧❧♦✇✐♥❣ ❧❡♠♠❛✳ ▲❡♠♠❛ ✶✳✷✼ ✭❬❇❛r✾✸❪✮✳ ▲❡t E ❜❡ ❛ s✐♠♣❧❡✲♣♦❧❡ ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ f t❤❡ C✲ ♠♦r♣❤✐s♠ ✐♥❞✉❝❡❞ ❜② b✁1a ♦♥ E④bE✳ ❋♦r ❡❛❝❤ λ P C ❡✐❣❡♥✈❛❧✉❡ ♦❢ f ❧❡t✿
λmin ✏ min tλ j, j P Z⑤λ j P Spec♣fq✉
❈❤❛♣t❡r ✷
❉✉❛❧✐t② ❛♥❞ ❤❡r♠✐t✐❛♥ ❢♦r♠s
■♥ t❤✐s ❝❤❛♣t❡r ✇❡ ✇✐❧❧ ✐♥tr♦❞✉❝❡ t❤❡ ❝♦♥❝❡♣t ♦❢ ❞✉❛❧✐t② ❢♦r ❛♥ ♣a, bq✲♠♦❞✲ ✉❧❡ E✳ ❚❤✐s ♥♦t✐♦♥ ✇❛s ✐♥tr♦❞✉❝❡❞ ❜② ❉✳ ❇❛r❧❡t ✐♥ ❬❇❛r✾✼❪ ❛♥❞ ❢✉rt❤❡r ❞❡✈❡❧♦♣❡❞ ❜② ❘✳ ❇❡❧❣r❛❞❡ ✐♥ ❬❇❡❧✵✶❪✳ ❚❤❡ ✜rst s❡❝t✐♦♥ ✇✐❧❧ ❜❡ ❞❡✈♦t❡❞ t♦ t❤❡ ❝♦♠♣❛r✐s♦♥ ♦❢ t❤❡ ❞❡✜♥✐t✐♦♥s ♦❢ ❞✉❛❧ ♣a, bq✲♠♦❞✉❧❡ ❣✐✈❡♥ ❜② ❉✳ ❇❛r❧❡t ❛♥❞ ❘✳ ❇❡❧❣r❛❞❡✳ ❲❡ ✇✐❧❧ r❡t❛✐♥ ❤❡r❡ t❤❡ ❞❡✜♥✐t✐♦♥ ♦❢ ❉✳ ❇❛r❧❡t✱ ✇❤✐❧❡ ✇❡✬❧❧ r❡❞✉❝❡ ❘✳ ❇❡❧❣r❛❞❡✬s ❞❡✜♥✐t✐♦♥ ♦❢ δ✲❞✉❛❧ t♦ t❤❡ ❝♦♥❝❡♣t ♦❢ ❛❞❥♦✐♥t ♣a, bq✲♠♦❞✲ ✉❧❡ ❛♥❞ t❡♥s♦r ♣r♦❞✉❝t✳ ❲❡ ✇✐❧❧ ♠♦r❡♦✈❡r ✐♥tr♦❞✉❝❡ ❤❡r♠✐t✐❛♥ ❢♦r♠s ♦♥ ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ r❡❧❛t❡ t❤❡♠ t♦ ✐s♦♠♦r♣❤✐s♠s ♦❢ ❛♥ ♣a, bq✲♠♦❞✉❧❡ ✇✐t❤ ✐ts ❛❞❥♦✐♥t✳ ❚❤❡ s❡❝♦♥❞ ❛♥❞ ❧❛st s❡❝t✐♦♥ ✇✐❧❧ ❞❡❛❧ ✇✐t❤ t❤❡ ❡①✐st❡♥❝❡ ♦❢ ❤❡r♠✐t✐❛♥ ♥♦♥ ❞❡❣❡♥❡r❛t❡ ❢♦r♠s ♦♥ ♣a, bq✲♠♦❞✉❧❡s✳ ❋♦r t❤✐s ♣✉r♣♦s❡ ✇❡ ✇✐❧❧ ✐♥tr♦❞✉❝❡ t❤❡ ❝♦♥❝❡♣t ♦❢ ✐♥❞❡❝♦♠♣♦s❛❜❧❡ ♠♦❞✉❧❡s ❛♥❞ ❣✐✈❡ t❤❡ ❞❡❝♦♠♣♦s✐t✐♦♥ ♦❢ ❛♥ ♣a, bq✲♠♦❞✉❧❡ ✐♥t♦ ✐ts ✐♥❞❡❝♦♠♣♦s❛❜❧❡ ♣❛rts✳✷✳✶ ❉✉❛❧✐t②
✷✳✶✳✶ ❇❛r❧❡t✬s ❞❡✜♥✐t✐♦♥
▲❡t E ❛♥❞ F ❜❡ t✇♦ ♣a, bq✲♠♦❞✉❧❡s✳ ❆s ❞❡✜♥❡❞ ❜② ❉✳ ❇❛r❧❡t ✐♥ ❬❇❛r✾✼❪✱ t❤❡ Crrbss✲♠♦❞✉❧❡ HomCrrbss♣E, F q ♦❢ Crrbss✲❧✐♥❡❛r ♠❛♣s ❢r♦♠ E t♦ F ❤❛s ❛ ♥❛t✉r❛❧ str✉❝t✉r❡ ♦❢ ♣a, bq✲♠♦❞✉❧❡ ♣r♦✈✐❞❡❞ ❜② ❛♥ ♦♣❡r❛t♦r Λ t❤❛t s❛t✐s✜❡s ♣Λϕq ♣xq ✏ aF ♣ϕ♣xqq ✁ ϕ ♣aExq , ✭✷✳✶✮ ✇❤❡r❡ ϕ P HomCrrbss♣E, F q✱ x ✐s ❛♥ ❡❧❡♠❡♥t ♦❢ E ❛♥❞ aE ❛♥❞ aF ❛r❡ t❤❡ a✲str✉❝t✉r❡s ♦❢ E ❛♥❞ F r❡s♣❡❝t✐✈❡❧②✳ ❲❡ ✇✐❧❧ ❞❡s✐❣♥❛t❡ t❤✐s ♣a, bq✲♠♦❞✉❧❡ ✇✐t❤ t❤❡ ♥♦t❛t✐♦♥ Hom♣a,bq♣E, F q✳ ❋♦r ♥♦t❛t✐♦♥✬s s❛❦❡ ✇❡ ✇✐❧❧ ❞❡♥♦t❡ aE✱ aF✸✵ ❈❍❆P❚❊❘ ✷✳ ❉❯❆▲■❚❨ ❆◆❉ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ❝♦✉❧❞ ♣♦s❡ ✇❡ s❤♦✉❧❞ r❡❛❞ t❤❡ ❡①♣r❡ss✐♦♥ a☎ ϕ♣xq ❛s ♣Λϕq ♣xq✱ ✇❤❡r❡❛s t❤❡ ❡①♣r❡ss✐♦♥ aE♣ϕ♣xqq ✇✐❧❧ ❦❡❡♣ t❤❡ ❝♦♥✈❡♥t✐♦♥❛❧ ♥♦✲ t❛t✐♦♥ aϕ♣xq. ❲❡ ✇✐❧❧ t❤❡r❡❢♦r❡ r❡✇r✐t❡ t❤❡ ❡q✉❛t✐♦♥ ✷✳✶ ❛s✿ a☎ ϕ♣xq ✏ aϕ♣xq ✁ ϕ♣axq. ❘❡♠❛r❦ ✷✳✶✳ ◆♦t❡ t❤❛t ✇❤❡r❡❛s HomCrrbss♣E, F q ✐s ❛ ❢r❡❡ Crrbss✲♠♦❞✉❧❡s ♦❢ ✜♥✐t❡ r❛♥❦✱ ✐t ✇❛s ♣r♦✈❡♥ ✐♥ t❤❡♦r❡♠ ✶ ❜✐s ♦❢ ❬❇❛r✾✼❪ t❤❛t t❤❡ ✈❡❝t♦r s♣❛❝❡ HomA˜♣E, F q ♦❢ ♣a, bq✲♠♦r♣❤✐s♠s ❜❡t✇❡❡♥ E ❛♥❞ F ✐s ♦❢ ✜♥✐t❡ C✲❞✐♠❡♥s✐♦♥
❛♥❞ t❤❡r❡❢♦r❡ ❝❛♥ ♥♦t ❤❛✈❡ ❛ str✉❝t✉r❡ ♦❢ ♣a, bq✲♠♦❞✉❧❡✳ ◆♦ ❝♦♥❢✉s✐♦♥ ❝❛♥ t❤❡r❡❢♦r❡ ❛r✐s❡ ✇❤❡♥ t❛❧❦✐♥❣ ❛❜♦✉t t❤❡ ♣a, bq✲♠♦❞✉❧❡ Hom♣a,bq♣E, F q✳
❇② ❝❤♦♦s✐♥❣ E0 ❢♦r t❤❡ ❝♦❞♦♠❛✐♥ ♦❢ t❤❡ ♠♦r♣❤✐s♠s✱ ✇❡ ❝❛♥ ❣✐✈❡ t❤❡
❢♦❧❧♦✇✐♥❣ ❞❡✜♥✐t✐♦♥✿
❉❡✜♥✐t✐♦♥ ✷✳✷ ✭❇❛r❧❡t✮✳ ▲❡t E ❜❡ ❛♥ ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ E0 t❤❡ ❡❧❡♠❡♥t❛r②
♣a, bq✲♠♦❞✉❧❡ ♦❢ ♣❛r❛♠❡t❡r 0✱ t❤❡♥ ✇❡ ❝❛❧❧ t❤❡ ♠♦❞✉❧❡
Hom♣a,bq♣E, E0q
t❤❡ ❞✉❛❧ ♣a, bq✲♠♦❞✉❧❡ ♦❢ E ❛♥❞ ♥♦t❡ ✐t ❜② E✝✳ ❘❡♠❛r❦ ✷✳✸✳ ❲❤❡♥ ❝♦♥s✐❞❡r✐♥❣ ♦♥❧② t❤❡ b✲str✉❝t✉r❡ ♦❢ E✱ t❤❡ Crrbss✲♠♦❞✉❧❡ E✝ ❝♦rr❡s♣♦♥❞s ❡①❛❝t❧② t♦ t❤❡ ❞❡✜♥✐t✐♦♥ ♦❢ ❞✉❛❧ ♦❢ ❛ Crrbss✲♠♦❞✉❧❡✱ s✐♥❝❡ E0 ✏ Crrbsse0✱ ✇✐t❤ ae0 ✏ 0✳ ❘❡♠❛r❦ ✷✳✹✳ ❚❤❡ ❞✉❛❧ ♦❢ t❤❡ ❡❧❡♠❡♥t❛r② ♣a, bq✲♠♦❞✉❧❡ Eλ ✐s ✐s♦♠♦r♣❤✐❝ t♦ E✁λ✳ ■♥ ❢❛❝t✱ ✐❢ ✇❡ ❝♦♥s✐❞❡r t❤❡ ❜❛s✐s teλ✉ ♦❢ Eλ ❛♥❞ te✝λ✉ t❤❡ ❞✉❛❧ ❜❛s✐s ♦❢ ♣Eλq✝ s✉❝❤ t❤❛t e✝λ♣eλq ✏ e0, ✇❤❡r❡ e0 ✐s t❤❡ ❣❡♥❡r❛t♦r ♦❢ E0✱ ✇❡ ❥✉st ❤❛✈❡ t♦ ❝❤❡❝❦ t❤❡ ❛❝t✐♦♥ ♦❢ a ♦♥ e✝λ t♦ ♦❜t❛✐♥ t❤❡ r❡s✉❧t✳ ❲❡ ❤❛✈❡ t❤❡r❡❢♦r❡✿
a☎ e✝λ♣eλq ✏ ae✝λ♣eλq ✁ e✝λ♣aeλq ✏ ae0✁ e✝λ♣λbeλq ✏ ✁λbe0 ✏ ✁λbe✝λ♣eλq
❛♥❞ ✇❡ ❤❛✈❡ s♦ ✈❡r✐✜❡❞ t❤❡ ❡q✉❛❧✐t②
a☎ e✝λ ✏ ✁λb ☎ e✝λ ♦♥ t❤❡ Crrbss✲❜❛s✐s te✝
✷✳✶✳ ❉❯❆▲■❚❨ ✸✶ ❲❤✐❧❡ t❤❡ ❡①❛♠♣❧❡ ❛❜♦✈❡ s❤♦✇s ✉s t❤❛t ❛♥ ♣a, bq✲♠♦❞✉❧❡ ✐s ♥♦t ✐♥ ❣❡♥❡r❛❧ ✐s♦♠♦r♣❤✐❝ t♦ ✐ts ❞✉❛❧✱ t❤❡r❡ ❡①✐sts ❛❧✇❛②s ❛♥ ✐s♦♠♦r♣❤✐s♠ ✇✐t❤ ✐ts ❜✐❞✉❛❧ E✝✝ ✏ ♣E✝q✝✳ ■♥ ❢❛❝t✿ Pr♦♣♦s✐t✐♦♥ ✷✳✺✳ ▲❡t E ❜❡ ❛♥ ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ E✝✝ ✏ ♣E✝q✝ ✐ts ❜✐❞✉❛❧ t❤❡♥ t❤❡ ♥❛t✉r❛❧ ❛♣♣❧✐❝❛t✐♦♥ can : E Ñ E✝✝ v ÞÑ ♣ˆv : ϕ ÞÑ ϕ♣vqq , ✇❤❡r❡ v P E ❛♥❞ ϕ P E✝✱ ✐s ❛♥ ✐s♦♠♦r♣❤✐s♠✳ Pr♦♦❢✳ ❙❡t✇✐s❡ t❤❡ ❛♣♣❧✐❝❛t✐♦♥ ❵can✬ ✐s t❤❡ s❛♠❡ ❛s t❤❡ ❝❛♥♦♥✐❝❛❧ ❛♣♣❧✐❝❛t✐♦♥ ❜❡t✇❡❡♥ E ❝♦♥s✐❞❡r❡❞ ❛s Crrbss✲♠♦❞✉❧❡ ❛♥❞ ✐ts Crrbss✲♠♦❞✉❧❡ ❞✉❛❧✳ ❚❤❡r❡❢♦r❡ ✐t ✐s ❛♥ ✐s♦♠♦r♣❤✐s♠ ♦❢ Crrbss✲♠♦❞✉❧❡s✳ ❲❡ ❤❛✈❡ ❥✉st t♦ ✈❡r✐❢② t❤❛t ✐t ♣r❡s❡r✈❡s t❤❡ a✲str✉❝t✉r❡✳ ❲❡ ✇✐❧❧ ❞❡♥♦t❡ t❤❡ ❛❝t✐♦♥ ♦❢ a ♦♥ E✝✝ ❜② a ☎ ☎✱ ✇❤✐❝❤ s❛t✐s✜❡s✿ a☎ ☎ˆv♣ϕq ✏ aˆv♣ϕq ✁ ˆv♣a ☎ ϕq, ❢♦r ❡❛❝❤ ˆv P E✝✝ ❛♥❞ ϕ P E✝✳ ❲✐t❤ t❤✐s ♥♦t❛t✐♦♥ ✇❡ ❤❛✈❡
♣a ☎ ☎ can♣vqq ♣ϕq ✏ a can♣vq♣ϕq ✁ can♣vq♣a ☎ ϕq ✏
✷✳✶✳ ❉❯❆▲■❚❨ ✸✸ ❉❡✜♥✐t✐♦♥ ✷✳✽ ✭❇❡❧❣r❛❞❡✮✳ ▲❡t E ❜❡ ❛♥ ♣a, bq✲♠♦❞✉❧❡✳ ❲❡ ❝❛❧❧ δ✲❞✉❛❧ ♦❢ E✱ δP C✱ t❤❡ Crrbss✲♠♦❞✉❧❡ HomCrrbss♣E, Eδq ❡♥❞♦✇❡❞ ✇✐t❤ ❛♥ ♣a, bq✲str✉❝t✉r❡ ❞❡✜♥❡❞ ❛s✿ ra ☎ ϕs♣xq ✏ ϕ♣axq ✁ aϕ♣xq rb ☎ ϕs♣xq ✏ ✁bϕ♣xq ✏ ϕ♣✁bxq, ✇✐t❤ ϕ P HomCrrbss♣E, Eδq ❛♥❞ x P E✳
✷✳✶✳ ❉❯❆▲■❚❨ ✸✺
✷✳✶✳✸ ❇✐❧✐♥❡❛r ❢♦r♠s ❛♥❞ t❡♥s♦r ♣r♦❞✉❝t
■♥ ♦r❞❡r t♦ ❞❡✜♥❡ Hom♣a,bq♣E, F q ✇❡ ✉s❡❞ t❤❡ ❡q✉✐✈❛❧❡♥t ♦❜❥❡❝t ❢♦r ✐ts
✉♥❞❡r❧②✐♥❣ b✲str✉❝t✉r❡✳ ❲❡ ✇✐❧❧ ✐♥tr♦❞✉❝❡ ✐♥ ❛ s✐♠✐❧❛r ♠❛♥♥❡r t❤❡ ❝♦♥❝❡♣t ♦❢ ❜✐❧✐♥❡❛r ♠❛♣ ♦❢ ♣a, bq✲♠♦❞✉❧❡s✿
❉❡✜♥✐t✐♦♥ ✷✳✶✸✳ ▲❡t E✱ F ❛♥❞ G ❜❡ t✇♦ ♣a, bq✲♠♦❞✉❧❡s✳ ❆♥ ♣a, bq✲❜✐❧✐♥❡❛r ❢♦r♠ ♦♥ E ✂ F ✐s ❛ Crrbss✲❧✐♥❡❛r ♠❛♣ Φ✱
Φ : E✂ F Ñ G, t❤❛t s❛t✐s✜❡s t❤❡ ❢♦❧❧♦✇✐♥❣ ♣r♦♣❡rt②✿
aΦ♣x, yq ✏ Φ♣ax, yq Φ♣x, ayq.
❘❡♠❛r❦ ✷✳✶✹✳ ■❢ Φ ✐s ❛♥ ♣a, bq✲❜✐❧✐♥❡❛r ♠❛♣ ♦♥ E ✂ F ✇✐t❤ ✈❛❧✉❡s ✐♥ G ❛♥❞ v ✐s ❛♥ ❡❧❡♠❡♥t ♦❢ E✿
Φv :✏ Φ♣v, ☎q : w ÞÑ Φ♣v, wq wP F
✐s ♥♦t ♥❡❝❡ss❛r✐❧② ❛♥ ♣a, bq✲♠♦r♣❤✐s♠✳ ❍♦✇❡✈❡r t❤❡ ♠❛♣ π : v ÞÑ Φv ✐s ❛♥
♣a, bq✲♠♦r♣❤✐s♠ ❜❡t✇❡❡♥ E ❛♥❞ Hom♣a,bq♣F, Gq✳ ❲❡ ❤❛✈❡ ✐♥ ❢❛❝t✿
π♣avq♣xq ✏ Φav♣xq ✏ aΦv♣xq ✁ Φv♣axq ✏ a ☎ Φv♣xq ✏ aπ♣vq.
■♥❤❡r❡♥t❧② ❧✐♥❦❡❞ t♦ t❤❡ ❝♦♥❝❡♣t ♦❢ ♣a, bq✲❜✐❧✐♥❡❛r ♠❛♣s ✐s t❤❛t ♦❢ t❡♥s♦r ♣r♦❞✉❝ts✱ t❤❛t ❛❧❧♦✇s ❛ ♠♦r❡ ♣r❛❝t✐❝❛❧ ♠❛♥✐♣✉❧❛t✐♦♥ ♦❢ t❤❡s❡ ♦❜❥❡❝ts✳ ❉❡✜♥✐t✐♦♥ ✷✳✶✺✳ ▲❡t E ❛♥❞ F ❜❡ t✇♦ ♣a, bq✲♠♦❞✉❧❡s✳ ❲❡ ❝❛❧❧ ♣a, bq✲t❡♥s♦r ♣r♦❞✉❝t ♦❢ E ❛♥❞ F ❛♥❞ ✇r✐t❡ ✐t ❛s E ❜♣a,bqF t❤❡ Crrbss✲♠♦❞✉❧❡ E❜CrrbssF ❡♥❞♦✇❡❞ ✇✐t❤ ❛♥ a✲str✉❝t✉r❡ ❞❡✜♥❡❞ ❛s ❢♦❧❧♦✇s✿ a♣v ❜ wq ✏ ♣avq ❜ w v ❜ ♣awq ❢♦r ❡✈❡r② v P E ❛♥❞ w P F ✳ ❚❤❡ a✲str✉❝t✉r❡ ✇❡ ❣❛✈❡ ♦♥ E ❜♣a,bqF ✐s ✇❡❧❧ ❞❡✜♥❡❞✳ ❲❡ ❤❛✈❡ ✐♥ ❢❛❝t✿
✸✻ ❈❍❆P❚❊❘ ✷✳ ❉❯❆▲■❚❨ ❆◆❉ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ❢♦r ❡❛❝❤ v P E✱ w P F ❛♥❞ ✐t s❛t✐s✜❡s ab ✁ ba ✏ b2✿ a♣bv ❜ wq ✁ ba ♣v ❜ wq ✏ ba♣vq ❜ w b2v❜ w bv ❜ a♣wq ✁ ba♣vq ❜ w ✁ bv ❜ a♣wq ✏ b2♣v ❜ wq . ❲❡ ❝❛♥ ❡❛s✐❧② ✈❡r✐❢② t❤❛t t❤❡ t❡♥s♦r ♣r♦❞✉❝t ❞❡✜♥❡❞ ✐♥ t❤✐s ✇❛② s❛t✐s✜❡s t❤❡ ✉s✉❛❧ ✉♥✐✈❡rs❛❧ ♣r♦♣❡rt②✿ t❤❡r❡ ❡①✐sts ❛ ❜✐❧✐♥❡❛r ♠❛♣ Φ : E✂ F Ñ E ❜♣a,bqF, s✉❝❤ t❤❛t ❢♦r ❡✈❡r② ❜✐❧✐♥❡❛r ♠❛♣ Ψ ♦♥ E✂F ✇✐t❤ ✈❛❧✉❡s ✐♥ ❛ t❤✐r❞ ♣a, bq✲♠♦❞✲ ✉❧❡ G✱ t❤❡r❡ ❡①✐sts ❛ ✉♥✐q✉❡ ♣a, bq✲♠♦r♣❤✐s♠ ˜Ψ ❢r♦♠ E ❜♣a,bqF ✐♥t♦ G t❤❛t ♠❛❦❡s t❤❡ ❢♦❧❧♦✇✐♥❣ ❞✐❛❣r❛♠ ❝♦♠♠✉t❛t✐✈❡✿ E✂ F Φ Ψ // G E❜♣a,bqF. ˜ Ψt t ::t t t ❲❡ ❝❛♥ t❛❦❡ ❛s Φ t❤❡ ♥❛t✉r❛❧ ❛♣♣❧✐❝❛t✐♦♥ Φ : E✂ F Ñ E ❜♣a,bqF ♣v, wq ÞÑ v ❜♣a,bqw ❛♥❞ ❞❡✜♥❡ ˜Ψ ❛s✿ ˜ Ψ : E❜♣a,bqF Ñ G v❜♣a,bqwÞÑ Ψ♣v, wq ❚❤❡ ✉♥✐❝✐t② ♦❢ ˜Ψ ❢♦❧❧♦✇s ❞✐r❡❝t❧② ❢r♦♠ t❤❡ ✉♥✐✈❡rs❛❧ ♣r♦♣❡rt② ♦❢ t❤❡ t❡♥s♦r ♣r♦❞✉❝t ♦❢ Crrbss✲♠♦❞✉❧❡s✳ ❲❡ ♥❡❡❞ ♦♥❧② ✈❡r✐❢② t❤❛t t❤❡ ♠❛♣ ✐s a✲❧✐♥❡❛r✳ ❲❡ ✇✐❧❧ ❞♦ ✐t ♦♥ t❤❡ ❣❡♥❡r❛t♦rs v ❜♣a,bqw ♦❢ E ❜♣a,bqF✱ ❢♦r v P E ❛♥❞ w P F ✿ ˜
Ψ a♣v ❜♣a,bqwq✟✏ ˜Ψ ♣avq ❜♣a,bqw v❜♣a,bq♣awq✟✏
Ψ♣av, wq Ψ♣v, awq ✏ aΨ♣v, wq ✏ a ˜Ψ♣v ❜♣a,bqwq. ■♥ ❛ s✐♠✐❧❛r ♠❛♥♥❡r✱ ❜② ✉s✐♥❣ t❤❡ ♣r♦♣❡rt✐❡s ♦❢ t❤❡ t❡♥s♦r ♣r♦❞✉❝t ♦❢ Crrbss✲♠♦❞✉❧❡s✱ ✇❡ ❝❛♥ ❞❡r✐✈❡ t❤❡ ♦t❤❡r ♣r♦♣❡rt✐❡s ♦❢ t❤❡ ❡q✉✐✈❛❧❡♥t ♦❜❥❡❝t ✐♥ t❤❡ t❤❡♦r② ♦❢ ♣a, bq✲♠♦❞✉❧❡s✳
✷✳✶✳ ❉❯❆▲■❚❨ ✸✼ ✭✐✮
E❜♣a,bqF ✔ F ❜♣a,bqE,
✭✐✐✮
E❜♣a,bqF✟❜♣a,bqG✔ E ❜♣a,bq F ❜♣a,bqG✟,
✭✐✐✐✮ E❜♣a,bqF✟✝ ✔ E✝❜♣a,bqF✝, ✭✐✈✮ E❜♣a,bqF✟˘✔ ˘E❜♣a,bqF ,˘ ✭✈✮ ❚❤❡ ♣a, bq✲♠♦r♣❤✐s♠ Φ : EÑ E ❜♣a,bqE0 v ÞÑ v ❜♣a,bqe0 ✇❤❡r❡ e0 ✐s ❛ ❣❡♥❡r❛t♦r ♦❢ t❤❡ ❡❧❡♠❡♥t❛r② ♣a, bq✲♠♦❞✉❧❡ E0✱ ✐s ❛♥ ✐s♦✲ ♠♦r♣❤✐s♠✳ ✭✈✐✮ ❲❡ ❤❛✈❡ t❤❡ ❢♦❧❧♦✇✐♥❣ ✐s♦♠♦r♣❤✐s♠ ♦❢ ♣a, bq✲♠♦❞✉❧❡s✿
E✝❜♣a,bqF Ñ Hom♣a,bq E, F ❜♣a,bqE0
✟
ϕ❜♣a,bqyÞÑ Φ : x ÞÑ y ❜♣a,bqϕ♣xq✟,
✇❤❡r❡ ϕ P E✝✱ x P E ❛♥❞ y P F ✳
❋r♦♠ ♣r♦♣❡rt② ✭✈✮ ❛♥❞ ✭✈✐✮ ✇❡ ❤❛✈❡ E✝❜
♣a,bqF ✔ Hom♣a,bq♣E, F q✱ ✇❤✐❝❤ ✐♥
✸✽ ❈❍❆P❚❊❘ ✷✳ ❉❯❆▲■❚❨ ❆◆❉ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ❘❡♠❛r❦ ✷✳✶✾✳ ❙✐♥❝❡ ❛ ♥♦♥❞❡❣❡♥❡r❛t❡ s❡q✉✐❧✐♥❡❛r ❢♦r♠ ♦♥ ❛♥ ♣a, bq✲♠♦❞✉❧❡ E ✐♥❞✉❝❡s ❛♥ ✐s♦♠♦r♣❤✐s♠ ♦❢ E ✇✐t❤ ✐ts ❛❞❥♦✐♥t ˘E✝ ✐t ❢♦❧❧♦✇s t❤❛t ♥♦t ❛❧❧ ♣a, bq✲♠♦❞✉❧❡s ❛r❡ s❡❧❢✲❛❞❥♦✐♥t ✭❡✳❣✳ Eλ ✇✐t❤ λ ✘ 0 ✐s ♥♦t✮ ❛♥❞ ♥♦t ❡✈❡r② ♣a, bq✲♠♦❞✉❧❡ ❛❞♠✐ts ❛ ♥♦♥❞❡❣❡♥❡r❛t❡ s❡sq✉✐❧✐♥❡❛r ❢♦r♠✳ ❈♦♥s✐❞❡r ♥♦✇ ❛ s❡sq✉✐❧✐♥❡❛r ❢♦r♠ Φ ♦♥ E✳ ❇② ❛♣♣❧②✐♥❣ t♦ ✐t t❤❡ ❝♦♥❥✉❣❛t❡ ❢✉♥❝t♦r ✇❡ ♦❜t❛✐♥ ❛ ❜✐❧✐♥❡❛r ♠❛♣ ˇΦ ♦♥ ˇE✂ E ✇✐t❤ ✈❛❧✉❡s ✐♥ ˇE0✳ ■❢ ✇❡ ✜① ❛♥ ✐s♦♠♦r♣❤✐s♠ ♦❢ ˇE0 ✇✐t❤ E0✱ ✇❡ ❝❛♥ ❝♦♥s✐❞❡r ˇΦ ❛s ❛ s❡q✉✐❧✐♥❡❛r ❢♦r♠ ♦♥ ˇE✳ ❯♥❞❡r t❤✐s ❛ss✉♠♣t✐♦♥✱ ✇❡ ❞❡✜♥❡ ♣a, bq✲❤❡r♠✐t✐❛♥ ❛♥❞ ❛♥t✐✲♣a, bq✲❤❡r♠✐t✐❛♥ ❢♦r♠s ❛s✿ ❉❡✜♥✐t✐♦♥ ✷✳✷✵✳ ▲❡t E ❜❡ ❛♥ ♣a, bq✲♠♦❞✉❧❡✳ ❆♥ ♣a, bq✲s❡sq✉✐❧✐♥❡❛r ❢♦r♠ H ♦♥ E ✐s ❝❛❧❧❡❞ ♣a, bq✲❤❡r♠✐t✐❛♥ ✭r❡s♣❡❝t✐✈❡❧② ❛♥t✐✲♣a, bq✲❤❡r♠✐t✐❛♥✮ ✐❢ ✐t s❛t✐s✜❡s✿ H♣v, wq ✏ ˇH♣w, vq, ✁ r❡s♣❡❝t✐✈❡❧② H♣v, wq ✏ ✁ ˘H♣w, vq✠. ✇❤❡r❡ v P E✱ w P ˘E ❛♥❞ ˘H ✐s t❤❡ s❡sq✉✐❧✐♥❡❛r ❢♦r♠ ♦♥ ˇE ❞❡✜♥❡❞ ❛❜♦✈❡✳ ❲❡ ❤❛✈❡ ❛❧r❡❛❞② s❤♦✇♥ t❤❛t ✐♥ ♦r❞❡r t♦ ❛❞♠✐t ❛ ♥♦♥❞❡❣❡♥❡r❛t❡ s❡sq✉✐❧✐♥✲ ❡❛r ❢♦r♠✱ ❛♥ ♣a, bq✲♠♦❞✉❧❡ ♠✉st ❜❡ s❡❧❢✲❛❞❥♦✐♥t✳ ❲❡ ✇✐❧❧ r❡✜♥❡ t❤❡ ❝♦♥❝❡♣t ♦❢ s❡❧❢✲❛❞❥♦✐♥t ❜② ❞❡✜♥✐♥❣✿ ❉❡✜♥✐t✐♦♥ ✷✳✷✶✳ ▲❡t E ❜❡ ❛ s❡❧❢✲❛❞❥♦✐♥t ♣a, bq✲♠♦❞✉❧❡✳ ❲❡ s❛② t❤❛t E ✐s ❤❡r♠✐t✐❛♥ ✭r❡s♣✳ ❛♥t✐✲❤❡r♠✐t✐❛♥✮✱ ✐❢ ✐t ❛❞♠✐ts ❛ ♥♦♥❞❡❣❡♥❡r❛t❡ ❤❡r♠✐t✐❛♥ ✭r❡s♣✳ ❛♥t✐✲❤❡r♠✐t✐❛♥✮ ❢♦r♠✳ ▲❡t E ❜❡ ❛♥ ♣a, bq✲♠♦❞✉❧❡ ❡♥❞♦✇❡❞ ✇✐t❤ ❛ ❤❡r♠✐t✐❛♥ ❢♦r♠ ❛♥❞ ❝♦♥s✐❞❡r Φ : E Ñ ˘E✝ t♦ ❜❡ t❤❡ ❧✐♥❡❛r ❢♦r♠ ❛ss♦❝✐❛t❡❞ t♦ t❤❡ ❤❡r♠✐t✐❛♥ ❢♦r♠ ✈✐❛ t❤❡ r❡♠❛r❦ ✷✳✶✹✳ ❲❡ ❝❛♥ tr❛♥s❧❛t❡ t❤❡ ❤❡r♠✐t✐❛♥ ♣r♦♣❡rt② ✐♥t♦ t❤❡ ✐❞❡♥t✐t② ❜❡t✇❡❡♥ Φ ❛♥❞ ✐ts ❛❞❥♦✐♥t ˇΦ✝ : EÑ ˘E✝✳ ■♥ ❢❛❝t ✇❤✐❧❡ Φ♣vq✱ ❢♦r v P E ✐s t❤❡ ❧✐♥❡❛r ♠❛♣✿ ϕ : wÞÑ Φ♣v, wq, wP ˇE, t❤❡ ❛❞❥♦✐♥t ♠❛♣ ˇΦ✝ s❡♥❞s ❛♥ ❡❧❡♠❡♥t v P E ✏ E✝✝ t♦ t❤❡ ♠❛♣✿ ϕ : w ÞÑ v ˇΦ♣w, ☎q✟✏ ˇΦ♣w, vq. ❲❡ ✇✐❧❧ ✉s❡ t❤✐s ❢♦r♠✉❧❛t✐♦♥ ❡①t❡♥s✐✈❡❧② ✐♥ t❤❡ ❢♦❧❧♦✇✐♥❣ s❡❝t✐♦♥✳ ◆♦t❡ ♠♦r❡♦✈❡r t❤❛t t♦ ❣✐✈❡ ❛♥ ✐s♦♠♦r♣❤✐s♠ Φ ❢r♦♠ ❛♥ ♣a, bq✲♠♦❞✉❧❡ E ❛♥❞ ✐ts δ✲❞✉❛❧ ˘E✝❜♣a,bqEδ✐s ❡q✉✐✈❛❧❡♥t t♦ s♣❡❝✐❢②✐♥❣ ❛♥ ✐s♦♠♦r♣❤✐s♠ ❜❡t✇❡❡♥ E❜♣a,bqE✁δ④2 ❛♥❞ ˘
✷✳✷✳ ❊❳■❙❚❊◆❈❊ ❖❋ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ✸✾ ❙✐♥❝❡ ✇❡ ❤❛✈❡
⑧
E❜♣a,bqE✁δ④2✟✝ ✔ ˘E✝❜♣a,bqEˇ✁δ④2✝ ✔ ˘E✝❜♣a,bqEδ④2,
✹✵ ❈❍❆P❚❊❘ ✷✳ ❉❯❆▲■❚❨ ❆◆❉ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ❚❤❡ ♣r♦♦❢ ♦❢ t❤✐s ♣r♦♣♦s✐t✐♦♥ ✇✐❧❧ ♥❡❡❞ s❡✈❡r❛❧ st❡♣s ❜❡❣✐♥♥✐♥❣ ✇✐t❤ ❛ ❞❡✜♥✐t✐♦♥✿ ❉❡✜♥✐t✐♦♥ ✷✳✷✹✳ ▲❡t E ❜❡ ❛ r❡❣✉❧❛r ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ λ P C✳ ❲❡ ❞❡✜♥❡✿ Vλ ✏ ✦➳ Fi⑤Fi ⑨ E, Fi ✔ Eλ ✮ , t❤❡ s✉♠ ♦❢ ❛❧❧ s✉❜✲♣a, bq✲♠♦❞✉❧❡s ♦❢ E ✐s♦♠♦r♣❤✐❝ t♦ Eλ✳ ❚❤❡ ♦❜❥❡❝t Vλ ✐s ❝❧❡❛r❧② ❛ s✉❜✲♣a, bq✲♠♦❞✉❧❡✳ ❲❡ ✇✐❧❧ ✉s❡ Vλ ❛s ❛♥ ✐♥❞✉❝✲ t✐♦♥ st❡♣ ✐♥ t❤❡ ♣r♦♦❢ ♦❢ ♣r♦♣♦s✐t✐♦♥ ✷✳✷✸✱ ❜② ❝❤♦♦s✐♥❣ s✉❝❤ ❛ λ t❤❛t Vλ ✐s ♥♦r♠❛❧✿ Pr♦♣♦s✐t✐♦♥ ✷✳✷✺✳ ▲❡t E ❜❡ ❛ r❡❣✉❧❛r ♣a, bq✲♠♦❞✉❧❡✱ λ P C ❛♥❞✿ λmin ✏ inf j tλ j⑤j P Z ❛♥❞ ❉x P E, ax ✏ ♣λ jqbx✉ ❜❡ t❤❡ ♠✐♥✐♠❛❧ λ j s✉❝❤ t❤❛t E ❝♦♥t❛✐♥s ❛ ♠♦♥♦♠✐❛❧ ♦❢ t②♣❡ ♣λ j, 0q✳ ❚❤❡♥ Vλmin ✐s ❛ ♥♦r♠❛❧ s✉❜✲♣a, bq✲♠♦❞✉❧❡ ♦❢ E ✐s♦♠♦r♣❤✐❝ ❛s ♣a, bq✲♠♦❞✉❧❡
t♦ t❤❡ ❞✐r❡❝t s✉♠ ♦❢ ❛ ✜♥✐t❡ ♥✉♠❜❡r ♦❢ ❝♦♣✐❡s ♦❢ Eλmin✳
Pr♦♦❢✳ ❲❡ ✇✐❧❧ ✉s❡ t✇♦ ❢❛❝ts✳
❋✐rst✱ ❢♦r ❡✈❡r② W ✔➚Eλmin s✉❜✲♣a, bq✲♠♦❞✉❧❡ ♦❢ E✱ W ✐s ♥♦r♠❛❧ ✐♥ E✳
✷✳✷✳ ❊❳■❙❚❊◆❈❊ ❖❋ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ✹✶ ❲❡ ✇✐❧❧ ♥♦✇ ✉s❡ t❤❡ s✉❜✲♣a, bq✲♠♦❞✉❧❡ Vλmin t♦ s❤♦✇ t❤❡ ❢♦❧❧♦✇✐♥❣ ♣r♦♣♦✲ s✐t✐♦♥ Pr♦♣♦s✐t✐♦♥ ✷✳✷✻✳ ▲❡t E ❜❡ ❛ r❡❣✉❧❛r ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ ❧❡t ϕ ❜❡ ❛ ♠♦r♣❤✐s♠ ❜❡t✇❡❡♥ E ❛♥❞ ✐ts❡❧❢✳ ❚❤❡♥ ϕ ✐s ❜✐❥❡❝t✐✈❡ ✐❢ ❛♥❞ ♦♥❧② ✐❢ ϕ ✐s ✐♥❥❡❝t✐✈❡✳ Pr♦♦❢✳ ❚♦ s❤♦✇ t❤❛t ❜✐❥❡❝t✐✈✐t② ❢♦❧❧♦✇s ❢r♦♠ ✐♥❥❡❝t✐✈✐t②✱ ✇❡ ✇✐❧❧ ♣r♦❝❡❡❞ ❜② ✐♥❞✉❝t✐♦♥ ♦♥ t❤❡ r❛♥❦ ♦❢ t❤❡ ♠♦❞✉❧❡✳ ■❢ E ✐s ♦❢ r❛♥❦ 1 t❤❡ st❛t❡♠❡♥t ♦❢ t❤❡ ♣r♦♦❢ ✐s s❛t✐s✜❡❞✿ ✐♥ ❢❛❝t E ♠✉st ❜❡ ✐s♦♠♦r♣❤✐❝ t♦ ♦♥❡ ♦❢ t❤❡ Eλ ❛♥❞ t❤❡ ♦♥❧② b✲❧✐♥❡❛r ♠♦r♣❤✐s♠s ❢r♦♠ ❛ Eλ t♦ ✐ts❡❧❢ t❤❛t ❛r❡ ❛❧s♦ a✲❧✐♥❡❛r ❛r❡ t❤♦s❡ t❤❛t s❡♥❞ t❤❡ ❣❡♥❡r❛t♦r e t♦ αe✱ α P C✳ ❚❤❡② ❛r❡ ❛❧❧ ❜✐❥❡❝t✐✈❡ ❢♦r α ✘ 0✳ ▲❡t ♥♦✇ E ❜❡ ♦❢ r❛♥❦ n → 1✳ ❲❡ ❝❛♥ ✜♥❞✱ ❜② ❧❡♠♠❛ ✶✳✷✼✱ ❛ λmin t❤❛t s❛t✐s✜❡s t❤❡ ♠✐♥✐♠❛❧✐t② ♣r♦♣❡rt② ♦❢ t❤❡ ♣r❡✈✐♦✉s ♣r♦♣♦s✐t✐♦♥✳ ❍❡♥❝❡ t❤❡ ♠♦❞✉❧❡ Vλmin ✐s ♥♦r♠❛❧ ❛♥❞ ✐s♦♠♦r♣❤✐❝ t♦ ❛ ❞✐r❡❝t s✉♠ ♦❢ Eλmin✳ ▲❡t tei✉ ❜❡ ❛ ❜❛s✐s ♦❢ Vλmin ❝♦♠♣♦s❡❞ ♦❢ ♠♦♥♦♠✐❛❧s ♦❢ t②♣❡ ♣λmin, 0q ❛♥❞ ❧❡t x ❛♥♦t❤❡r ♠♦♥♦♠✐❛❧ ♦❢ t②♣❡ ♣λmin, 0q✳ ❲❡ ✇❛♥t t♦ s❤♦✇ t❤❛t x ✐s ❛ ❧✐♥❡❛r ❝♦♠❜✐♥❛t✐♦♥ ♦❢ t❤❡ ❡❧❡♠❡♥ts ♦❢ t❤❡ ❜❛s✐s✱ ✇✐t❤ ❝♦❡✣❝✐❡♥ts ✐♥ C ⑨ Crrbss✳ ❋r♦♠ t❤❡ ❞❡✜♥✐t✐♦♥ ♦❢ Vλmin ❢♦❧❧♦✇s t❤❛t x P Vλmin✳ ❙✉♣♣♦s❡ ♥♦✇ t❤❛t x✏➦iSi♣bqei ❛♥❞ ❧❡t ✉s ❛♣♣❧② a t♦ ❜♦t❤ s✐❞❡s✳ ❲❡ ♦❜t❛✐♥✿ ax✏➳ i λminSi♣bqbei Si✶♣bqb 2e i ✟ ✏ λminbx ➳ i Si✶♣bqb2ei ❛♥❞ s✐♥❝❡ x ✐s ❛ ♠♦♥♦♠✐❛❧ ♦❢ t②♣❡ ♣λmin, 0q✱ ✇❡ ♠✉st ❤❛✈❡ S✶♣bqi ✏ 0 ❢♦r ❛❧❧ i ❛♥❞ t❤❡r❡❢♦r❡ x✏➳ i Si♣0qei, ❛s ✇❡ ✇❛♥t❡❞✳ ▲❡t ϕ : E Ñ E ❜❡ ❛♥ ✐♥❥❡❝t✐✈❡ ❡♥❞♦♠♦r♣❤✐s♠ ♦❢ E ❛♥❞ tei✉ ❛ ❜❛s✐s ♦❢
Vλmin✳ ❊✈❡r② ϕ♣eiq ✐s ❛ ♠♦♥♦♠✐❛❧ ♦❢ t②♣❡ ♣λmin, 0q ❛♥❞ t❤❡r❡❢♦r❡ ✐s ❛♥ ❡❧❡♠❡♥t
♦❢ Vλmin✳ ❚❤❡ r❡str✐❝t✐♦♥ ♦❢ ϕ t♦ Vλmin ✐s t❤❡r❡❢♦r❡ ❛♥ ❡♥❞♦♠♦r♣❤✐s♠ ♦❢ Vλmin✿
ϕ⑤Vλmin : Vλmin Ñ Vλmin.
✹✷ ❈❍❆P❚❊❘ ✷✳ ❉❯❆▲■❚❨ ❆◆❉ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ✇❤❡r❡ ˜ϕ ✐s t❤❡ ♣a, bq✲❧✐♥❡❛r ♠♦r♣❤✐s♠ ✐♥❞✉❝❡❞ ♦♥ t❤❡ q✉♦t✐❡♥t✳ ❆s ✇❡ s❤♦✇❡❞ t❤❡ ✜rst ❞♦✇♥✇❛r❞ ❛rr♦✇ ✐s ❜✐❥❡❝t✐✈❡✳
❚❤❡ t❤✐r❞ ❛rr♦✇ ˜ϕ ✐s ✐♥❥❡❝t✐✈❡✿ s✉♣♣♦s❡ ✐♥ ❢❛❝t t❤❛t ✇❡ ❤❛✈❡ t✇♦ ❞✐✛❡r❡♥t ❝❧❛ss❡s ✇✐t❤ r❡♣r❡s❡♥t❛t✐✈❡s x ❛♥❞ y P E t❤❛t ♠❛♣ t♦ t❤❡ s❛♠❡ ❝❧❛ss ♠♦❞✉❧♦ Vλmin✳ ❚❤❡♥ ϕ♣x ✁ yq ✐s ✐♥ Vλmin✳ ❋r♦♠ t❤❡ ❜✐❥❡❝t✐✈✐t② ♦❢ ϕ⑤Vλmin ✇❡ ❝❛♥ ✜♥❞
❛♥ ❡❧❡♠❡♥t v P Vλmin s✉❝❤ t❤❛t
ϕ♣x ✁ yq ✏ ϕ♣vq
✇❤✐❝❤ ✐♥ t✉r♥ ✐♠♣❧✐❡s x ✁ y ✏ v ❜② t❤❡ ✐♥❥❡❝t✐✈✐t② ♦❢ ϕ✱ ✇❤✐❝❤ ❝♦♥tr❛❞✐❝ts t❤❡ ❢❛❝t t❤❛t x ❛♥❞ y ❛r❡ ✐♥ ❞✐st✐♥❝t ❝❧❛ss❡s ♠♦❞✉❧♦ Vλmin✳
❙✐♥❝❡ t❤❡ r❛♥❦ ♦❢ E④Vλmin ✐s str✐❝t❧② ✐♥❢❡r✐♦r t♦ t❤❡ r❛♥❦ ♦❢ E✱ ✇❡ ❝❛♥
✹✽ ❈❍❆P❚❊❘ ✷✳ ❉❯❆▲■❚❨ ❆◆❉ ❍❊❘▼■❚■❆◆ ❋❖❘▼❙ ■t ✐s ♥♦✇ ❡❛s② t♦ ❝❤❡❝❦ t❤❛t t❤❡ ♠❛♣ ❣✐✈❡♥ ❜②✿ Φ : E Ñ E✝ e1 ÞÑ ˇe✝4 e2 ÞÑ ✁ˇe✝3 e3 ÞÑ ˇe✝2 e4 ÞÑ ✁ˇe✝1 ✐s ❛♥ ✐s♦♠♦r♣❤✐s♠ ❛♥❞ ✐s ❛♥t✐✲s❡❧❢✲❛❞❥♦✐♥t✳ ■❢ ✇❡ ❝❤♦♦s❡ λ ❛♥❞ µ s✉❝❤ t❤❛t ♥♦♥❡ ♦❢ t❤❡ ♥✉♠❜❡rs 2λ✱ 2µ ❛♥❞ λ ✟ µ ✐s ❛♥ ✐♥t❡❣❡r✱ t❤✐s ♠♦❞✉❧❡ ✐s ✐♥❞❡❝♦♠♣♦s❛❜❧❡ ❛♥❞ ❞♦❡s ♥♦t ❛❞♠✐t ❛ ❤❡r♠✐t✐❛♥ ❢♦r♠✳ ❲❡ ❝❛♥ s❤♦✇ t❤❛t t❤❡ str✉❝t✉r❡ ♦❢ t❤✐s ♠♦❞✉❧❡ ✐s ✐♥ ❢❛❝t ✈❡r② r✐❣✐❞ ❛♥❞ t❤❡ ♦♥❧② ❡❧❡♠❡♥ts ♦❢ t❤❡ ♣a, bq✲♠♦❞✉❧❡ t❤❛t ✈❡r✐❢② t❤❡ ❡q✉❛t✐♦♥s ✷✳✸ ❛r❡ t❤❡ 4✲t✉♣❧❡ts tαe1, αe2, αe3, αe4✉✱ ❢♦r α r❛♥❣✐♥❣ ❛♠♦♥❣ t❤❡ ❝♦♠♣❧❡① ♥✉♠❜❡rs✿ ❧❡t
✺✹ ❈❍❆P❚❊❘ ✸✳ ❙❊▲❋✲❆❉❏❖■◆❚ ❈❖▼P❖❙■❚■❖◆ ❙❊❘■❊❙ ❘❡♠❛r❦ ✸✳✸✳ ■❢ aeλ ✏ λbeλ ❛♥❞ 2λ ❘ N✱ t❤❡♥ H♣eλ, eλq ✏ 0✳ ■♥ ❢❛❝t
H♣eλ, eλq P E0 ♠✉st ✈❡r✐❢②✿
aH♣eλ, eλq ✏ H♣aeλ, eλq H♣eλ,✁aeλq ✏ 2λbH♣eλ, eλq
✻✷ ❈❍❆P❚❊❘ ✹✳ ❍■●❍❊❘✲❘❊❙■❉❯❊ P❆■❘■◆●❙ ✇✐t❤ x✱ y P E✳ ◆♦t✐❝❡ t❤❛t t❤✐s ❞❡✜♥✐t✐♦♥ ❞✐✛❡rs ❢r♦♠ t❤❛t ♦❢ ❘✳ ❇❡❧❣r❛❞❡ ❜② ❛ ❢❛❝t♦r ♦❢ ♣n 1q!✳
✹✳✷ ✏❍✐❣❤❡r r❡s✐❞✉❡ ♣❛✐r✐♥❣s✑ ♦❢ ❑✳ ❙❛✐t♦
❑✳ ❙❛✐t♦ ✐♥tr♦❞✉❝❡❞ ✐♥ ❬❙❛✐✽✸❪ ❛ s❡r✐❡s ♦❢ ♣❛✐r✐♥❣s ♦♥ t❤❡ ❇r✐❡s❦♦r♥ ❧❛tt✐❝❡ D ✇❤✐❝❤ ❛r❡ ❝❛❧❧❡❞ ✏❤✐❣❤❡r r❡s✐❞✉❡ ♣❛✐r✐♥❣s✑✿ K♣kq: D✂ D Ñ C k P N ✇❤✐❝❤ ❛r❡ ❝❤❛r❛❝t❡r✐③❡❞ ❜② t❤❡ ❢♦❧❧♦✇✐♥❣ ♣r♦♣❡rt✐❡s✿ ✭✐✮ K♣kq♣ω 1, ω2q ✏ K♣k 1q♣bω1, ω2q ✏ ✁K♣k 1q♣ω1, bω2q✳ ✭✐✐✮ K♣kq♣aω 1, ω2q ✁ K♣kq♣ω1, aω2q ✏ ♣n kqK♣k✁1q♣ω1, ω2q✳ ✭✐✐✐✮ K♣0q s❛t✐s✜❡s K♣0q♣D, bDq ✏ K♣0q♣bD, Dq ✏ 0 ❛♥❞ ✐♥❞✉❝❡s ●r♦t❤❡♥❞✐❡❝❦✬s r❡s✐❞✉❡ ♦♥ t❤❡ q✉♦t✐❡♥t D④bD✳ ✭✐✈✮ K♣kq ❛r❡ ♣✁1qk✲s②♠♠❡tr✐❝✳ ❘❡♠❛r❦ ✹✳✷✳ ❲❡ ♥♦t✐❝❡ t❤❛t ❢r♦♠ t❤❡ ♣r♦♣❡rt✐❡s ✭✐✮ ❛♥❞ ✭✐✐✐✮ ❛❜♦✈❡ ✇❡ ❝❛♥ ❞❡❞✉❝❡ t❤❛t K♣kq♣D, bk 1Dq ✏ K♣kq♣bk 1D, Dq ✏ 0✱ s♦ ✇❡ ❝❛♥ ❝♦♥s✐❞❡r t❤❡ ♣❛✐r✐♥❣s K♣kq ❛s ❜❡✐♥❣ ❞❡✜♥❡❞ ♦♥ D④bk 1D✳ ■♥ t❤❡ ❢♦❧❧♦✇✐♥❣ s❡❝t✐♦♥ ✇❡✬❧❧ s❤♦✇ t❤❡ ❢♦❧❧♦✇✐♥❣ r❡s✉❧t✿ Pr♦♣♦s✐t✐♦♥ ✹✳✸✳ ❚❤❡ ∆k✈❡r✐❢② t❤❡ ♣r♦♣❡rt✐❡s ✭✐✮✕✭✐✐✐✮ ♦❢ t❤❡ ✏❤✐❣❤❡r r❡s✐❞✉❡ ♣❛✐r✐♥❣s✑ ♦❢ ❑✳ ❙❛✐t♦✳ ❚❤❡ ♣r♦✈❡ ✇✐❧❧ ❜❡ ♣❡r❢♦r♠❡❞ ❜② st❡♣s✳✹✳✸ Pr♦♦❢ ♦❢ t❤❡ ♣r♦♣♦s✐t✐♦♥
✹✳✸✳✶ Pr♦♦❢ ♦❢ ✭✐✮
❲❡ ✉s❡ t❤❡ b✲❧✐♥❡❛r✐t② ♦❢ ∆♣yq t♦ ♦❜t❛✐♥✿ ➳ k♣n 1q!∆k♣bx, yqbken 1 ✏ r∆♣yqs ♣bxq ✏ b r∆♣yqs ♣xq ✏
➳
k
✹✳✸✳ P❘❖❖❋ ❖❋ ❚❍❊ P❘❖P❖❙■❚■❖◆ ✻✸ ✇❤✐❝❤ ❣✐✈❡s ✉s ∆k♣x, yq ✏ ∆k 1♣bx, yq✳ ❆♥❞ s✐♠✐❧❛r❧② ❜② ✉s✐♥❣ t❤❡ b✲❧✐♥❡❛r✐t②
♦❢ ∆ ❛♥❞ t❤❡ ❞❡✜♥✐t✐♦♥ ♦❢ ❝♦♥❥✉❣❛t❡✱ ✇❡ ♦❜t❛✐♥✿
∆♣byq♣xq ✏ ♣b ☎Eˇ✝ ∆♣yqq ♣xq ✏ ✁b∆♣yq♣xq,
❛♥❞ t❤❡r❡❢♦r❡
♣n 1q!➳
k
∆k♣x, byqbken 1 ✏ ∆♣byq♣xq ✏ ✁b∆♣yq♣xq ✏
♣n 1q!➳ k ✁∆k♣x, yqbk 1en 1 ✇❤✐❝❤ ✐♠♣❧✐❡s ∆k♣bx, yq ✏ ✁∆k 1♣x, byq✳
✹✳✸✳✷ Pr♦♦❢ ♦❢ ✭✐✐✮
❙✐♥❝❡ ∆ ✐s ❛♥ ✐s♦♠♦r♣❤✐s♠ ✇❡ ❤❛✈❡ ∆♣ayq ✏ a ☎Eˇ✝ r∆♣yqs ❛♥❞✿ ♣n 1q!➳ k∆k♣x, ayqbken 1✏ ∆♣ayq♣xq ✏ a ☎ r∆♣yqs♣xq ✏
✏ ∆♣yq♣axq ✁ ar∆♣yq♣xqs ✏ ♣n 1q!➳
k
∆k♣ax, yqbken 1✁ ∆k♣x, yqabken 1
✟ ❚❤❡ ❞❡✜♥✐t✐♦♥ ♦❢ ♣a, bq✲♠♦❞✉❧❡ ❛♥❞ En 1 ✭aen 1 ✏ ♣n 1qben 1✮ ❣✐✈❡s t❤❡