-
The globally hyperbolic splitting in non-smoothLorentzian
manifolds
Clemens Sämann
joint work withGünther Hörmann
University of Vienna, AustriaFaculty of Mathematics
DIANA group
ISAAC, Krakow, August 5, 2013
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 1 /
10
-
Introduction
Global hyperbolicity: strongest causality condition,
well-posedness of theCauchy problem
(M , g) a space-time, i.e., a time-oriented, connected
Lorentzian manifold(M , g) is globally hyperbolic if one of the
following equivalent conditions issatisfied:
(M , g) is causal and ∀p, q ∈ M with q ∈ J +(p): J +(p) ∩ J−(q)
iscompactThere is a Cauchy hypersurface S in (M , g)(M , g) is
isometric to R× S , where S is a Cauchy hypersurface in M
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 2 /
10
-
Introduction
Global hyperbolicity: strongest causality condition,
well-posedness of theCauchy problem
(M , g) a space-time, i.e., a time-oriented, connected
Lorentzian manifold(M , g) is globally hyperbolic if one of the
following equivalent conditions issatisfied:
(M , g) is causal and ∀p, q ∈ M with q ∈ J +(p): J +(p) ∩ J−(q)
iscompactThere is a Cauchy hypersurface S in (M , g)(M , g) is
isometric to R× S , where S is a Cauchy hypersurface in M
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 2 /
10
-
Introduction
Global hyperbolicity: strongest causality condition,
well-posedness of theCauchy problem
(M , g) a space-time, i.e., a time-oriented, connected
Lorentzian manifold(M , g) is globally hyperbolic if one of the
following equivalent conditions issatisfied:
(M , g) is causal and ∀p, q ∈ M with q ∈ J +(p): J +(p) ∩ J−(q)
iscompactThere is a Cauchy hypersurface S in (M , g)(M , g) is
isometric to R× S , where S is a Cauchy hypersurface in M
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 2 /
10
-
Introduction
Global hyperbolicity: strongest causality condition,
well-posedness of theCauchy problem
(M , g) a space-time, i.e., a time-oriented, connected
Lorentzian manifold(M , g) is globally hyperbolic if one of the
following equivalent conditions issatisfied:
(M , g) is causal and ∀p, q ∈ M with q ∈ J +(p): J +(p) ∩ J−(q)
iscompactThere is a Cauchy hypersurface S in (M , g)(M , g) is
isometric to R× S , where S is a Cauchy hypersurface in M
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 2 /
10
-
Introduction
Global hyperbolicity: strongest causality condition,
well-posedness of theCauchy problem
(M , g) a space-time, i.e., a time-oriented, connected
Lorentzian manifold(M , g) is globally hyperbolic if one of the
following equivalent conditions issatisfied:
(M , g) is causal and ∀p, q ∈ M with q ∈ J +(p): J +(p) ∩ J−(q)
iscompactThere is a Cauchy hypersurface S in (M , g)(M , g) is
isometric to R× S , where S is a Cauchy hypersurface in M
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 2 /
10
-
The smooth metric splitting
want: generalization of global hyperbolicity to non-smooth
Lorentzianmanifoldsapproach: via the globally hyperbolic metric
splitting
Theorem (Bernal, Sánchez 2005)Let (M , g) be a globally
hyperbolic Lorentzian manifold, then (M , g) isisometric to (R× S
,−βdt2 + ht), where S is a smooth spacelike Cauchyhypersurface, t :
R× S → R is the projection on the first factor,β : R× S → (0,∞) a
smooth function, and ht is a Riemannian metric oneach St := {t} × S
, which varies smoothly with t.
strengthening of Geroch’s topological splitting (1970)
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 3 /
10
-
The smooth metric splitting
want: generalization of global hyperbolicity to non-smooth
Lorentzianmanifoldsapproach: via the globally hyperbolic metric
splitting
Theorem (Bernal, Sánchez 2005)Let (M , g) be a globally
hyperbolic Lorentzian manifold, then (M , g) isisometric to (R× S
,−βdt2 + ht), where S is a smooth spacelike Cauchyhypersurface, t :
R× S → R is the projection on the first factor,β : R× S → (0,∞) a
smooth function, and ht is a Riemannian metric oneach St := {t} × S
, which varies smoothly with t.
strengthening of Geroch’s topological splitting (1970)
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 3 /
10
-
The smooth metric splitting
want: generalization of global hyperbolicity to non-smooth
Lorentzianmanifoldsapproach: via the globally hyperbolic metric
splitting
Theorem (Bernal, Sánchez 2005)Let (M , g) be a globally
hyperbolic Lorentzian manifold, then (M , g) isisometric to (R× S
,−βdt2 + ht), where S is a smooth spacelike Cauchyhypersurface, t :
R× S → R is the projection on the first factor,β : R× S → (0,∞) a
smooth function, and ht is a Riemannian metric oneach St := {t} × S
, which varies smoothly with t.
strengthening of Geroch’s topological splitting (1970)
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 3 /
10
-
The smooth metric splitting
want: generalization of global hyperbolicity to non-smooth
Lorentzianmanifoldsapproach: via the globally hyperbolic metric
splitting
Theorem (Bernal, Sánchez 2005)Let (M , g) be a globally
hyperbolic Lorentzian manifold, then (M , g) isisometric to (R× S
,−βdt2 + ht), where S is a smooth spacelike Cauchyhypersurface, t :
R× S → R is the projection on the first factor,β : R× S → (0,∞) a
smooth function, and ht is a Riemannian metric oneach St := {t} × S
, which varies smoothly with t.
strengthening of Geroch’s topological splitting (1970)
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 3 /
10
-
N -fronted waves with parallel rays (NPWs) (1/2)
Definition (NPWs)N-fronted waves with parallel rays (NPWs), are
space-times with Lorentzmetric
π∗(h) + 2dudv − a(., u)du2
on M := N × R2, where (N , h) is a connected Riemannian
manifold.
Profile function a : N × R→ R, π : N × R→ N projectionN as wave
surfacean NPW is globally hyperbolic if (N , h) is complete and a
behavessubquadraticallya(x, u) = f (x)δ(u) ; impulsive
gravitational waves
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 4 /
10
-
N -fronted waves with parallel rays (NPWs) (1/2)
Definition (NPWs)N-fronted waves with parallel rays (NPWs), are
space-times with Lorentzmetric
π∗(h) + 2dudv − a(., u)du2
on M := N × R2, where (N , h) is a connected Riemannian
manifold.
Profile function a : N × R→ R, π : N × R→ N projectionN as wave
surfacean NPW is globally hyperbolic if (N , h) is complete and a
behavessubquadraticallya(x, u) = f (x)δ(u) ; impulsive
gravitational waves
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 4 /
10
-
N -fronted waves with parallel rays (NPWs) (1/2)
Definition (NPWs)N-fronted waves with parallel rays (NPWs), are
space-times with Lorentzmetric
π∗(h) + 2dudv − a(., u)du2
on M := N × R2, where (N , h) is a connected Riemannian
manifold.
Profile function a : N × R→ R, π : N × R→ N projectionN as wave
surfacean NPW is globally hyperbolic if (N , h) is complete and a
behavessubquadraticallya(x, u) = f (x)δ(u) ; impulsive
gravitational waves
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 4 /
10
-
N -fronted waves with parallel rays (NPWs) (1/2)
Definition (NPWs)N-fronted waves with parallel rays (NPWs), are
space-times with Lorentzmetric
π∗(h) + 2dudv − a(., u)du2
on M := N × R2, where (N , h) is a connected Riemannian
manifold.
Profile function a : N × R→ R, π : N × R→ N projectionN as wave
surfacean NPW is globally hyperbolic if (N , h) is complete and a
behavessubquadraticallya(x, u) = f (x)δ(u) ; impulsive
gravitational waves
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 4 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
N -fronted waves with parallel rays (NPWs) (2/2)
Special case M = R2, 0 ≤ a < λ(u0, v0) ∈ R2
a(u0) gives the slope of the lightlike linev = a(u0)2 uspacelike
line S = {(u, λu) : u ∈ R}indicates the “maximal” slope
Behaviour of lightcones
v
u
∂v
space
space
future
past
slope a(u0)2
S
(M , g) is globally hyperbolic if a ∈ C∞(N ×R) with 0 ≤ a < λ
and (N , h)is complete
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 5 /
10
-
The non-smooth metric splitting for NPWs (1/3)
First explicit calculations in the smooth case, then use these
�-wise
M = N × R2 an NPW with a ∈ C∞(N × R) and 0 ≤ a < λ
τλ : M → R, τλ(x, u, v) := λu − v is a time function for (M ,
g)if DN
ξ̇ξ̇ = 12∇xa(ξ, α) has complete trajectories or M = R
2 thenSkλ := τ
−1λ ({k}) = {(x, u, λu − k) : x ∈ N , u ∈ R} is a Cauchy
hypersurface for every k ∈ Runder these hypotheses we obtain the
metric splitting explicitly
Theorem (G. Hörmann, C.S. 2013)(M , g) is isometric to (R× S ,
l), where S = S0λ and
l = −12λ−Adt2 + Ht .
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 6 /
10
-
The non-smooth metric splitting for NPWs (1/3)
First explicit calculations in the smooth case, then use these
�-wise
M = N × R2 an NPW with a ∈ C∞(N × R) and 0 ≤ a < λ
τλ : M → R, τλ(x, u, v) := λu − v is a time function for (M ,
g)if DN
ξ̇ξ̇ = 12∇xa(ξ, α) has complete trajectories or M = R
2 thenSkλ := τ
−1λ ({k}) = {(x, u, λu − k) : x ∈ N , u ∈ R} is a Cauchy
hypersurface for every k ∈ Runder these hypotheses we obtain the
metric splitting explicitly
Theorem (G. Hörmann, C.S. 2013)(M , g) is isometric to (R× S ,
l), where S = S0λ and
l = −12λ−Adt2 + Ht .
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 6 /
10
-
The non-smooth metric splitting for NPWs (1/3)
First explicit calculations in the smooth case, then use these
�-wise
M = N × R2 an NPW with a ∈ C∞(N × R) and 0 ≤ a < λ
τλ : M → R, τλ(x, u, v) := λu − v is a time function for (M ,
g)if DN
ξ̇ξ̇ = 12∇xa(ξ, α) has complete trajectories or M = R
2 thenSkλ := τ
−1λ ({k}) = {(x, u, λu − k) : x ∈ N , u ∈ R} is a Cauchy
hypersurface for every k ∈ Runder these hypotheses we obtain the
metric splitting explicitly
Theorem (G. Hörmann, C.S. 2013)(M , g) is isometric to (R× S ,
l), where S = S0λ and
l = −12λ−Adt2 + Ht .
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 6 /
10
-
The non-smooth metric splitting for NPWs (1/3)
First explicit calculations in the smooth case, then use these
�-wise
M = N × R2 an NPW with a ∈ C∞(N × R) and 0 ≤ a < λ
τλ : M → R, τλ(x, u, v) := λu − v is a time function for (M ,
g)if DN
ξ̇ξ̇ = 12∇xa(ξ, α) has complete trajectories or M = R
2 thenSkλ := τ
−1λ ({k}) = {(x, u, λu − k) : x ∈ N , u ∈ R} is a Cauchy
hypersurface for every k ∈ Runder these hypotheses we obtain the
metric splitting explicitly
Theorem (G. Hörmann, C.S. 2013)(M , g) is isometric to (R× S ,
l), where S = S0λ and
l = −12λ−Adt2 + Ht .
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 6 /
10
-
The non-smooth metric splitting for NPWs (1/3)
First explicit calculations in the smooth case, then use these
�-wise
M = N × R2 an NPW with a ∈ C∞(N × R) and 0 ≤ a < λ
τλ : M → R, τλ(x, u, v) := λu − v is a time function for (M ,
g)if DN
ξ̇ξ̇ = 12∇xa(ξ, α) has complete trajectories or M = R
2 thenSkλ := τ
−1λ ({k}) = {(x, u, λu − k) : x ∈ N , u ∈ R} is a Cauchy
hypersurface for every k ∈ Runder these hypotheses we obtain the
metric splitting explicitly
Theorem (G. Hörmann, C.S. 2013)(M , g) is isometric to (R× S ,
l), where S = S0λ and
l = −12λ−Adt2 + Ht .
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 6 /
10
-
The non-smooth metric splitting for NPWs (1/3)
First explicit calculations in the smooth case, then use these
�-wise
M = N × R2 an NPW with a ∈ C∞(N × R) and 0 ≤ a < λ
τλ : M → R, τλ(x, u, v) := λu − v is a time function for (M ,
g)if DN
ξ̇ξ̇ = 12∇xa(ξ, α) has complete trajectories or M = R
2 thenSkλ := τ
−1λ ({k}) = {(x, u, λu − k) : x ∈ N , u ∈ R} is a Cauchy
hypersurface for every k ∈ Runder these hypotheses we obtain the
metric splitting explicitly
Theorem (G. Hörmann, C.S. 2013)(M , g) is isometric to (R× S ,
l), where S = S0λ and
l = −12λ−Adt2 + Ht .
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 6 /
10
-
The non-smooth metric splitting for NPWs (2/3)
non-smooth profile function a : N × R→ R, Riemannian metric h
onN still smooth(a�)� a net of smooth functions N × R→ R with 0 ≤
a� < λ for all� ∈ (0, 1], depending smoothly on � and moderate,
hence defines aclass in G(N × R)g := [(g�)�] ∈ G02(M ), where g has
representative
g� := π∗(h) + 2dudv − a�(., u)du2
so (M , g) is a generalized Lorentzian manifoldunder the
assumptions before we obtain �-wise the metric splitting
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 7 /
10
-
The non-smooth metric splitting for NPWs (2/3)
non-smooth profile function a : N × R→ R, Riemannian metric h
onN still smooth(a�)� a net of smooth functions N × R→ R with 0 ≤
a� < λ for all� ∈ (0, 1], depending smoothly on � and moderate,
hence defines aclass in G(N × R)g := [(g�)�] ∈ G02(M ), where g has
representative
g� := π∗(h) + 2dudv − a�(., u)du2
so (M , g) is a generalized Lorentzian manifoldunder the
assumptions before we obtain �-wise the metric splitting
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 7 /
10
-
The non-smooth metric splitting for NPWs (2/3)
non-smooth profile function a : N × R→ R, Riemannian metric h
onN still smooth(a�)� a net of smooth functions N × R→ R with 0 ≤
a� < λ for all� ∈ (0, 1], depending smoothly on � and moderate,
hence defines aclass in G(N × R)g := [(g�)�] ∈ G02(M ), where g has
representative
g� := π∗(h) + 2dudv − a�(., u)du2
so (M , g) is a generalized Lorentzian manifoldunder the
assumptions before we obtain �-wise the metric splitting
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 7 /
10
-
The non-smooth metric splitting for NPWs (2/3)
non-smooth profile function a : N × R→ R, Riemannian metric h
onN still smooth(a�)� a net of smooth functions N × R→ R with 0 ≤
a� < λ for all� ∈ (0, 1], depending smoothly on � and moderate,
hence defines aclass in G(N × R)g := [(g�)�] ∈ G02(M ), where g has
representative
g� := π∗(h) + 2dudv − a�(., u)du2
so (M , g) is a generalized Lorentzian manifoldunder the
assumptions before we obtain �-wise the metric splitting
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 7 /
10
-
The non-smooth metric splitting for NPWs (3/3)
; generalized diffeomorphism between (M , g) and (R× S , l),
whichis c-bounded and its inverse alsothis yields the globally
hyperbolic metric splitting (Hörmann,Kunzinger, Steinbauer 2012),
i.e., the generalized metric l satisfies(a) ∃ representative (l�)
of l such that every l� is a Lorentzian metric and
each slice {t} × S is a Cauchy hypersurface for every l�(b) ∃
metric splitting of l in the form l = −βdt2 + ht
ht is a t-dependent generalized Riemannian metric on S ,β ∈ G(R×
S) is globally bounded, locally uniformly positive
(c) ∀T > 0 ∃ representative (hε) of h and a smooth complete
Riemannianmetric ρ on S such that
hεt (X ,X) ≥ ρ(X ,X) ∀t ∈ [−T ,T ] ∀X ∈ X(M )
uniformly in ε
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 8 /
10
-
The non-smooth metric splitting for NPWs (3/3)
; generalized diffeomorphism between (M , g) and (R× S , l),
whichis c-bounded and its inverse alsothis yields the globally
hyperbolic metric splitting (Hörmann,Kunzinger, Steinbauer 2012),
i.e., the generalized metric l satisfies(a) ∃ representative (l�)
of l such that every l� is a Lorentzian metric and
each slice {t} × S is a Cauchy hypersurface for every l�(b) ∃
metric splitting of l in the form l = −βdt2 + ht
ht is a t-dependent generalized Riemannian metric on S ,β ∈ G(R×
S) is globally bounded, locally uniformly positive
(c) ∀T > 0 ∃ representative (hε) of h and a smooth complete
Riemannianmetric ρ on S such that
hεt (X ,X) ≥ ρ(X ,X) ∀t ∈ [−T ,T ] ∀X ∈ X(M )
uniformly in ε
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 8 /
10
-
The non-smooth metric splitting for NPWs (3/3)
; generalized diffeomorphism between (M , g) and (R× S , l),
whichis c-bounded and its inverse alsothis yields the globally
hyperbolic metric splitting (Hörmann,Kunzinger, Steinbauer 2012),
i.e., the generalized metric l satisfies(a) ∃ representative (l�)
of l such that every l� is a Lorentzian metric and
each slice {t} × S is a Cauchy hypersurface for every l�(b) ∃
metric splitting of l in the form l = −βdt2 + ht
ht is a t-dependent generalized Riemannian metric on S ,β ∈ G(R×
S) is globally bounded, locally uniformly positive
(c) ∀T > 0 ∃ representative (hε) of h and a smooth complete
Riemannianmetric ρ on S such that
hεt (X ,X) ≥ ρ(X ,X) ∀t ∈ [−T ,T ] ∀X ∈ X(M )
uniformly in ε
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 8 /
10
-
The non-smooth metric splitting for NPWs (3/3)
; generalized diffeomorphism between (M , g) and (R× S , l),
whichis c-bounded and its inverse alsothis yields the globally
hyperbolic metric splitting (Hörmann,Kunzinger, Steinbauer 2012),
i.e., the generalized metric l satisfies(a) ∃ representative (l�)
of l such that every l� is a Lorentzian metric and
each slice {t} × S is a Cauchy hypersurface for every l�(b) ∃
metric splitting of l in the form l = −βdt2 + ht
ht is a t-dependent generalized Riemannian metric on S ,β ∈ G(R×
S) is globally bounded, locally uniformly positive
(c) ∀T > 0 ∃ representative (hε) of h and a smooth complete
Riemannianmetric ρ on S such that
hεt (X ,X) ≥ ρ(X ,X) ∀t ∈ [−T ,T ] ∀X ∈ X(M )
uniformly in ε
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 8 /
10
-
The non-smooth metric splitting for NPWs (3/3)
; generalized diffeomorphism between (M , g) and (R× S , l),
whichis c-bounded and its inverse alsothis yields the globally
hyperbolic metric splitting (Hörmann,Kunzinger, Steinbauer 2012),
i.e., the generalized metric l satisfies(a) ∃ representative (l�)
of l such that every l� is a Lorentzian metric and
each slice {t} × S is a Cauchy hypersurface for every l�(b) ∃
metric splitting of l in the form l = −βdt2 + ht
ht is a t-dependent generalized Riemannian metric on S ,β ∈ G(R×
S) is globally bounded, locally uniformly positive
(c) ∀T > 0 ∃ representative (hε) of h and a smooth complete
Riemannianmetric ρ on S such that
hεt (X ,X) ≥ ρ(X ,X) ∀t ∈ [−T ,T ] ∀X ∈ X(M )
uniformly in ε
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 8 /
10
-
Applications and Outlook
a0 ∈ L∞(N × R) with a0 ≥ 0 almost everywhere, ‖a0‖∞ < λ
andthere is a function C : R→ (0,∞) that is locally integrable
satisfying
|a0(x, s)− a0(y, s)| ≤ C (s) dh(x, y) (∀x, y ∈ N , s ∈ R) ,
then M ∼= R× S via a local bi-Lipschitz homeomorphisma0 as
above, not necessarily with the Lipschitz condition and (a�)�
asbefore with a� → a0 in L1loc(N × R), then the
correspondingdiffeomorphisms converge in L1loc(R× S)approximation
via appropriate convolution “a� := a0 ∗ ρ�”apply existence and
uniqueness result of the Cauchy problem(Hörmann, Kunzinger,
Steinbauer 2012) in this case
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 9 /
10
-
Applications and Outlook
a0 ∈ L∞(N × R) with a0 ≥ 0 almost everywhere, ‖a0‖∞ < λ
andthere is a function C : R→ (0,∞) that is locally integrable
satisfying
|a0(x, s)− a0(y, s)| ≤ C (s) dh(x, y) (∀x, y ∈ N , s ∈ R) ,
then M ∼= R× S via a local bi-Lipschitz homeomorphisma0 as
above, not necessarily with the Lipschitz condition and (a�)�
asbefore with a� → a0 in L1loc(N × R), then the
correspondingdiffeomorphisms converge in L1loc(R× S)approximation
via appropriate convolution “a� := a0 ∗ ρ�”apply existence and
uniqueness result of the Cauchy problem(Hörmann, Kunzinger,
Steinbauer 2012) in this case
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 9 /
10
-
Applications and Outlook
a0 ∈ L∞(N × R) with a0 ≥ 0 almost everywhere, ‖a0‖∞ < λ
andthere is a function C : R→ (0,∞) that is locally integrable
satisfying
|a0(x, s)− a0(y, s)| ≤ C (s) dh(x, y) (∀x, y ∈ N , s ∈ R) ,
then M ∼= R× S via a local bi-Lipschitz homeomorphisma0 as
above, not necessarily with the Lipschitz condition and (a�)�
asbefore with a� → a0 in L1loc(N × R), then the
correspondingdiffeomorphisms converge in L1loc(R× S)approximation
via appropriate convolution “a� := a0 ∗ ρ�”apply existence and
uniqueness result of the Cauchy problem(Hörmann, Kunzinger,
Steinbauer 2012) in this case
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 9 /
10
-
Applications and Outlook
a0 ∈ L∞(N × R) with a0 ≥ 0 almost everywhere, ‖a0‖∞ < λ
andthere is a function C : R→ (0,∞) that is locally integrable
satisfying
|a0(x, s)− a0(y, s)| ≤ C (s) dh(x, y) (∀x, y ∈ N , s ∈ R) ,
then M ∼= R× S via a local bi-Lipschitz homeomorphisma0 as
above, not necessarily with the Lipschitz condition and (a�)�
asbefore with a� → a0 in L1loc(N × R), then the
correspondingdiffeomorphisms converge in L1loc(R× S)approximation
via appropriate convolution “a� := a0 ∗ ρ�”apply existence and
uniqueness result of the Cauchy problem(Hörmann, Kunzinger,
Steinbauer 2012) in this case
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 9 /
10
-
References
A. N. Bernal, M. Sánchez. On smooth Cauchy hypersurfaces and
Geroch’ssplitting theorem. Commun. Math. Phys., 243(3):461–470,
2003.
A. N. Bernal, M. Sánchez. Smoothness of time functions and the
metricsplitting of globally hyperbolic spacetimes. Commun. Math.
Phys.,257(1):43-50, 2005.
J. L. Flores, M. Sánchez. On the geometry of pp-wave type
spacetimes. InAnalytical and numerical approaches to mathematical
relativity, volume 692of Lecture Notes in Phys., pages 79–98.
Springer, Berlin, 2006.
G. Hörmann, M. Kunzinger, R. Steinbauer. Wave equations on
non-smoothspace-times. In Evolution Equations of Hyperbolic and
Schrödinger Type,volume 301 of Progress in Mathematics, pages
163–186. Birkhäuser, 2012
G. Hörmann, C. S. The globally hyperbolic metric splitting for
non-smoothwave-type space-times. In preparation
Clemens Sämann, University of Vienna ISAAC, August 5, 2013 10 /
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