Curvature of Hamiltonian perturbations and the Floer energy identity #
Inhomogeneous Floer equations on a Riemann surface with coordinates z = (s, t) are perturbed by
a Hamiltonian-valued one-form K = K_s ds + K_t dt, given here by two families of Hamiltonians
Ks Kt : ℝ × ℝ → V → ℝ on a symplectic vector space (V, ω). Writing X_F for the Hamiltonian
vector field (ω(X_F, ·) = dF) and {F, G} = ω(X_F, X_G) for the Poisson bracket, we define:
- the curvature
R_K = ∂_s K_t - ∂_t K_s - {K_s, K_t}, a function of(z, x); - the perturbed derivative
du - X_K = du - ds ⊗ X_{K_s}(u) - dt ⊗ X_{K_t}(u)of a mapu : ℝ × ℝ → V; - the Floer energy density
ω(∂_s u - X_{K_s}(u), ∂_t u - X_{K_t}(u)).
The Floer equation (du - X_K)^{0,1} = 0 says that the perturbed derivative is complex linear for
the standard complex structure on ℝ × ℝ, or in coordinates
∂_s u - X_{K_s}(u) + J (∂_t u - X_{K_t}(u)) = 0. Since the energy density is by definition
the symplectic area density of the perturbed derivative, for solutions it is nonnegative under
tameness (SymplecticForm.floerEnergyDensity_nonneg) and is half the metric energy density
|du - X_K|², by IsComplexLinearMap.stdComplexLineEnergyDensity_eq_two_mul_symplecticForm.
For a merely tame J the form ω(·, J ·) is not a metric, so the energy is compared with the norm
instead: if c ‖v‖² ≤ ω(v, J v) and ‖J v‖ ≤ M ‖v‖, the energy density of a solution bounds
c (‖∂_s u - X_{K_s}‖² + ‖∂_t u - X_{K_t}‖²) up to the factor 1 + M², pointwise and after
integration. Such constants exist uniformly over a compact set of tamed structures
(IsCompact.exists_pos_forall_mul_norm_sq_le), so on a compact window of tamed structures the
energy bounds the L² norm of the perturbed derivative.
The main result is the energy identity: pointwise,
ω(∂_s u - X_{K_s}, ∂_t u - X_{K_t}) = ω(∂_s u, ∂_t u) + d(K(u)) - R_K(u),
where d(K(u)) = ∂_s (K_t(u)) - ∂_t (K_s(u)) is the exterior derivative of the pulled-back
one-form K(u) = K_s(u) ds + K_t(u) dt. Integrated over a rectangle using Stokes' formula,
the energy is the symplectic area plus the boundary integral of K(u) minus the integral of the
curvature. Curvature bounds therefore turn into energy bounds. For a cylindrical perturbation
K = H_t dt, the curvature vanishes; for the perturbation K = H_{(s, t)} dt of a homotopy of
Hamiltonians, it is ∂_s H_{(s, t)}, and in particular for a continuation perturbation
K = β(s) H_t dt it is β'(s) H_t.
Main definitions #
TauCeti.SymplecticForm.hamiltonianCurvature: the curvatureR_K.TauCeti.SymplecticForm.hamiltonianOneForm: the vector-valued one-formX_K = ds ⊗ X_{K_s} + dt ⊗ X_{K_t}.TauCeti.SymplecticForm.perturbedFDeriv: the perturbed derivativedu - X_K.TauCeti.SymplecticForm.floerEnergyDensity: the Floer energy density.TauCeti.SymplecticForm.stripEnergyMeasure: the measure onℝgiving each setAofs-values the energy overA × [0, 1].
Main results #
SymplecticForm.floerEnergyDensity_eq: the pointwise energy identity.SymplecticForm.floerEnergyDensity_nonneg: the energy density of a solution is nonnegative.SymplecticForm.floerEnergyDensity_eq_zero_iff: under tameness, the energy density of a solution vanishes exactly where the perturbed derivative does.SymplecticForm.mul_norm_sq_add_norm_sq_perturbedFDeriv_le_mul_floerEnergyDensityandSymplecticForm.setLIntegral_norm_sq_add_norm_sq_perturbedFDeriv_le: the energy controls the perturbed derivative, pointwise and inL².SymplecticForm.norm_fderiv_stdComplexLineReal_sq_le: the energy density and the Hamiltonian vector field control‖∂_s u‖².SymplecticForm.integral_floerEnergyDensity: the energy identity on a rectangle.SymplecticForm.integral_floerEnergyDensity_sub_add_eq_of_eventuallyEq_zero: the energy minus the symplectic area plus the integrated curvature does not change when a compact domain is shrunk to a part outside which the perturbation vanishes locally.SymplecticForm.floerEnergyDensity_add_hamiltonianCurvature_eq: for aC²map, the energy density plus the curvature is the exterior derivative of the one-formK(u) + λ(u), whereλₓ(v) = ½ ω(x, v)is the primitive ofω; this globalizes the energy identity to domains that are not rectangles.SymplecticForm.isComplexLinearMap_perturbedFDeriv_iff: the coordinate form of the Floer equation.SymplecticForm.hamiltonianCurvature_zero_left,SymplecticForm.hamiltonianCurvature_cylindrical,SymplecticForm.hamiltonianCurvature_homotopy,SymplecticForm.hamiltonianCurvature_continuation: the curvature of perturbations withoutdscomponent. Its local form along a line near which the perturbation is cylindrical isSymplecticForm.hamiltonianCurvature_eq_zero_of_cylindrical, the constant-form case of the manifold statement inTauCeti.Geometry.Symplectic.Floer.Manifold.SymplecticForm.perturbedFDeriv_add_const,SymplecticForm.floerEnergyDensity_add_const,SymplecticForm.hamiltonianCurvature_add_const: adding a target-independent one-formk = k_s ds + k_t dttoKchanges neither the perturbed derivative nor the energy density, and adds∂_s k_t - ∂_t k_sto the curvature (SymplecticForm.hamiltonianCurvature_const).SymplecticForm.hamiltonianCurvature_congr_of_eventuallyEq,SymplecticForm.hamiltonianCurvature_comp_add_right: the curvature is local in the domain and commutes with domain translations (so data that agree on an open set have the same integrated curvature over it,SymplecticForm.setLIntegral_enorm_hamiltonianCurvature_congr_of_isOpen), and likewise for the perturbed derivative (SymplecticForm.perturbedFDeriv_congr_of_eventuallyEq,SymplecticForm.perturbedFDeriv_comp_add_right) and the energy density (SymplecticForm.floerEnergyDensity_congr_of_eventuallyEq,SymplecticForm.floerEnergyDensity_comp_add_right); hence translations preserve the energy (SymplecticForm.lintegral_floerEnergyDensity_comp_add_right) and translate the strip energy measure (SymplecticForm.stripEnergyMeasure_comp_add_right).
References #
- D. McDuff and D. Salamon, J-holomorphic curves and symplectic topology, Section 8.1, on Hamiltonian perturbations, their curvature and the energy identity.
- P. Seidel, Fukaya categories and Picard–Lefschetz theory, Section 8, on inhomogeneous pseudoholomorphic maps and their energy.
The ∂_s derivative of a product β(s) h(t) is β'(s) h(t). This is the domain part of the
curvature of a continuation perturbation K = β(s) H_t dt, for any target.
The ∂_s derivative of a family H_t(x) independent of s vanishes. This is the domain part
of the curvature of a cylindrical perturbation K = H_t dt, for any target.
The curvature R_K = ∂_s K_t - ∂_t K_s - {K_s, K_t} of the Hamiltonian perturbation one-form
K = K_s ds + K_t dt, at the domain point z = (s, t) and the target point x.
Instances For
Without a ds component, the curvature of K = K_t dt is ∂_s K_t.
A cylindrical perturbation K = H_t dt, independent of s, has zero curvature.
The curvature of a homotopy of Hamiltonians. A perturbation K = H_{(s, t)} dt without
ds component, given by a family H_{(s, t)} of Hamiltonians, has curvature ∂_s H_{(s, t)}.
A continuation perturbation K = β(s) H_t dt has curvature β'(s) H_t.
The cylindrical perturbation K = H_t dt of a Cⁿ time-dependent Hamiltonian is Cⁿ.
The curvature only depends on the germs of the perturbation data at the domain point.
Perturbation data that agree on an open set have the same integrated curvature over it.
If both components of a Hamiltonian one-form vanish near a domain point, its curvature vanishes there. No differentiability assumption is needed.
If both components of a Hamiltonian one-form vanish off a closed domain set, its curvature also vanishes off that set. No differentiability assumption is needed.
Adding a perturbation supported in a closed set inside an open region where the original one-form vanishes adds their curvatures exactly: there are no mixed Poisson-bracket terms.
Curvature commutes with translations of the domain.
The perturbed derivative du - X_K of a map u at z, for the perturbation one-form
K = K_s ds + K_t dt: it sends a tangent vector (a, b) to du(a, b) - a X_{K_s} - b X_{K_t},
with the Hamiltonian vector fields evaluated at u z.
Instances For
The Hamiltonian vector field X_K = ds ⊗ X_{K_s} + dt ⊗ X_{K_t} of the perturbation one-form
K = K_s ds + K_t dt, at the domain point z and the target point x: it sends a tangent vector
(a, b) of the domain to a X_{K_s}(x) + b X_{K_t}(x).
Instances For
On an open set of (ℝ × ℝ) × V, the Hamiltonian one-form of a jointly C^(n+1) perturbation
is jointly Cⁿ.
The perturbed derivative is du - X_K(u).
The ∂_s component of the perturbed derivative is ∂_s u - X_{K_s}(u).
The ∂_t component of the perturbed derivative is ∂_t u - X_{K_t}(u).
The Floer equation in coordinates. The perturbed derivative is complex linear, that is
(du - X_K)^{0,1} = 0, exactly when ∂_s u - X_{K_s}(u) + J (∂_t u - X_{K_t}(u)) = 0.
The perturbed derivative commutes with translations of the domain: translating the map and
the perturbation data by v translates the perturbed derivative by v.
The perturbed derivative at z only depends on the germ of the map at z.
The perturbed derivative at z only depends on the components of the perturbation at z.
The Floer energy density ω(∂_s u - X_{K_s}(u), ∂_t u - X_{K_t}(u)) of a map u at z:
the symplectic area density of the perturbed derivative.
Instances For
For the zero perturbation the Floer energy density is the symplectic area density
ω(∂_s u, ∂_t u).
The Floer energy density commutes with translations of the domain.
The Floer energy density at z only depends on the germ of the map at z.
The Floer energy density at z only depends on the values K_s(z) and K_t(z) of the
perturbation at z, not on its derivatives.
The pointwise energy identity. The Floer energy density is the symplectic area density
ω(∂_s u, ∂_t u), plus the exterior derivative ∂_s (K_t(u)) - ∂_t (K_s(u)) of the pulled-back
one-form K(u), minus the curvature R_K(u).
Nonnegativity of the Floer energy density. If the perturbed derivative of u at z is
complex linear for an almost complex structure J tamed by ω, that is if u solves the Floer
equation at z, then the Floer energy density at z is nonnegative.
The Floer energy density of a solution of the Floer equation
∂_s u + J (∂_t u - X_{K_t}(u)) = 0 at z, for the perturbation K = K_t dt with a
domain-dependent Hamiltonian K_t, is nonnegative when J is tamed by ω.
For a solution of the Floer equation at z, the t-component of the perturbed derivative is
J applied to its s-component a = ∂_s u - X_{K_s}, so the Floer energy density is
ω(a, J a).
For a solution of the Floer equation with J tamed by ω, the Floer energy density at z
vanishes exactly when the perturbed derivative du - X_K vanishes at z.
Coercivity of the Floer energy density. Let u solve the Floer equation at z for an
almost complex structure J with c ‖v‖² ≤ ω(v, J v) and ‖J v‖ ≤ M ‖v‖ for all v, where
0 ≤ c. Then the energy density controls both components of the perturbed derivative:
c (‖∂_s u - X_{K_s}‖² + ‖∂_t u - X_{K_t}‖²) ≤ (1 + M²) ω(∂_s u - X_{K_s}, ∂_t u - X_{K_t}).
For J ranging over a compact set of tamed structures, uniform constants c > 0 and M exist
by IsCompact.exists_pos_forall_mul_norm_sq_le and the boundedness of compact sets.
The energy density bounds the derivative. Let u solve the Floer equation at z for an
almost complex structure J with c ‖v‖² ≤ ω(v, J v) for all v, where 0 < c. Then ∂_s u is
controlled by the energy density and the Hamiltonian vector field:
‖∂_s u‖² ≤ 2 / c · ω(∂_s u - X_{K_s}, ∂_t u - X_{K_t}) + 2 ‖X_{K_s}(u)‖².
The energy density plus the curvature is exact. For a C² map u into a symplectic
vector space and a perturbation K = K_s ds + K_t dt, the Floer energy density plus the
curvature R_K(u) is the exterior derivative ∂_s α_t - ∂_t α_s of the one-form
α = K(u) + λ(u), where λₓ(v) = ½ ω(x, v) is the primitive of ω.
Target-independent perturbations #
Adding to K a one-form k = k_s ds + k_t dt whose components are functions of the domain point
alone changes no Hamiltonian vector field. The perturbed derivative, and with it the Floer equation
and the energy density, are unchanged, while the curvature changes by the exterior derivative
∂_s k_t - ∂_t k_s of k. Normalizing the Hamiltonians on the ends by functions of time is the
main example.
The curvature of a target-independent perturbation k = k_s ds + k_t dt is the exterior
derivative ∂_s k_t - ∂_t k_s; the Poisson bracket term vanishes.
A target-independent perturbation has no Hamiltonian vector fields, so its perturbed derivative is the derivative of the map.
Adding a target-independent one-form to the perturbation adds its exterior derivative to the
curvature: R_{K + k} = R_K + ∂_s k_t - ∂_t k_s, at a point where the components are
differentiable in the domain.
Adding a target-independent one-form to the perturbation does not change the Hamiltonian
one-form X_K.
Adding a target-independent one-form to the perturbation does not change the perturbed
derivative, so a map solves the Floer equation for K + k exactly when it solves it for K.
Adding a target-independent one-form to the perturbation does not change the Floer energy density.
Translations preserve the energy. Translating the map and the perturbation data by v
preserves the energy: the energy of the translate over (· + v) ⁻¹' S is the energy of the
original over S.
For a map and perturbation data that are C¹ over an open set U of the domain, the Floer
energy density is continuous on U.
For perturbation data that is C¹ over an open set U of the domain, the curvature evaluated
along a map continuous on U is continuous on U.
For C¹ perturbation data, the curvature evaluated along a continuous map is continuous.
The energy identity on a rectangle. For a map u and perturbation data that are C¹ over
an open neighbourhood of a rectangle [a₁, b₁] × [a₂, b₂], the integral of the Floer energy
density over the rectangle is the symplectic area, plus the integral of the pulled-back one-form
K(u) = K_s(u) ds + K_t(u) dt over the positively oriented boundary, minus the integral of the
curvature R_K(u).
Shrinking to where the datum lives. Let the perturbation data be C¹ over an open set
P of the domain, let u be C¹ on P, and let T ⊆ D ⊆ P with D compact. If K_s and
K_t vanish near every point of D \ T, then the Floer energy minus the symplectic area plus the
integrated curvature is the same over D as over T.
The energy controls the perturbed derivative in L². Let u solve the Floer equation on
a measurable set U for domain-dependent almost complex structures J z satisfying
c ‖v‖² ≤ ω(v, J z v) and ‖J z v‖ ≤ M ‖v‖ on U, with 0 < c. Then the integral over U of
‖∂_s u - X_{K_s}‖² + ‖∂_t u - X_{K_t}‖² is at most (1 + M²) / c times the energy over U.
No measurability of the integrands is assumed.
The strip energy measure of a map u of the strip ℝ × [0, 1]: the measure on ℝ giving
each set A of s-values the Floer energy of u over A × [0, 1] for the perturbation data
Ks, Kt (TauCeti.SymplecticForm.stripEnergyMeasure_apply). It is the pushforward to the
s-axis of the energy density on the strip.
Instances For
The strip energy measure is the pushforward to the s-axis of the measure with density the
positive part of the energy density on the strip.
The strip energy measure of a measurable set A is the energy over A × [0, 1].
The total mass of the strip energy measure is the energy over the strip.
The strip energy measure of a map of finite energy is finite.
The strip energy measure vanishes exactly when the energy over the strip does.
Translations translate the strip energy measure. Translating a map and its perturbation
data by (c, 0) translates its strip energy measure by -c.
For the cylindrical perturbation K = H_t dt, translating the map by (c, 0) translates its
strip energy measure by -c.