Large deviations of the giant in spatial random graphs
Joost Jorritsma
joint with Júlia Komjáthy, Dieter Mitsche



Chennai Mathematical Institute, December '24
Supercritical Erdős–Rényi random graph G(n,λ/n)
[Erdős, Rényi '59; ...; O'Connell '98; Andreis, König, Langhammer, Patterson'23]
Exponential growth of neighbourhood
The largest component

Supercritical bond percolation on Zd

[Alexander, Chayes, Chayes '90; Cerf '00; Gandolfi '88; Grimmett & Marstrand '90, Kesten & Zhang '90, Pisztora '96, ...]
Surface-tension driven behavior
The largest component

Soft Poisson Boolean model
Edge set E∞
- {u↔v}⟺{wu1/d+wv1/d≥∥xu−xv∥}
- Long-range parameter α>1,
- Percolation p∈(0,1]
Connection probability
P(u↔v∣V∞)=p(∥xu−xv∥wu1/d+wv1/d∧1)αd
P(u↔v∣V∞)=p(∥xu−xv∥wu1/d+wv1/d∧1)αd
Vertex set V∞
- Locations: Poisson point process intensity β>0
- Power-law i.i.d. weights τ>2:
P(wv≥w)=w−(τ−1), w≥1
P(u↔v∣V∞)=p(∥xu−xv∥wu1/d+wv1/d∧1)αd




(deg(v)∣wv=w)=Poi(cα,d,τpβ⋅w)
Soft Poisson Boolean model




Supercriticality assumption
- θ=θd,τ,α,p(β):=Pd,τ,α,p,β0(0↔∞)
- β>βc(α,τ,d,p):=inf{β:θ(β)>0}
Edge set E∞
- {u↔v}⟺{wu1/d+wv1/d≥∥xu−xv∥}
- Long-range parameter α>1,
- Percolation p∈(0,1]
Vertex set V∞
- Locations: Poisson point process intensity β>0
- Power-law i.i.d. weights τ>2:
P(wv≥w)=w−(τ−1), w≥1
Soft Poisson Boolean model
Questions:
Fixed parameters:
- Point process on Rd intensity β>0
- Power-law exponent τ>2
- Long-range parameter α>1
- Percolation p∈(0,1]
[Gracar, Lüchtrath, Mönch '21]
- When is βc<∞?
- d≥2,
- Size of the largest connected component ∣Cn(1)∣
- Law of large numbers (∣Cn(1)∣/n→θ)?
- surface-tension behav. in P(∣Cn(1)∣/n<θ−ε)?
- exponential decay of P(∣Cn(1)∣/n>θ+ε)?
or d=1, and α∈(1,2∨ατ)



Power-law weights
Constant weights
Lower tail*:
If E[#edges of length n1/d]→∞
Main result: large deviations for the giant component
*log-corrections at non-unique maxima
Upper tail:
If non-critical
*at continuity points of I(θ+ε)
Biskup ['04]
Lower tail: a too small largest component

Goal 1: Law of large numbers
+ local convergence (Giant is almost local)
[vdHofstad, vdHoorn, Maitra '21, vdHofstad '21]
Goal 2: Prove the theorem
k→∞limn→∞limP0(∣Cn(0)∣>k,0∈/Cn(1))=0
∣Cn(2)∣=Θ(polylog(n))
Edge set E∞
- Long-range parameter α>1,
- Percolation p∈(0,1]
Connection probability
Vertex set V∞
- Locations: Poisson point process intensity β>0
- Power-law i.i.d. weights τ>2:
P(wv≥w)=w−(τ−1), w≥1
P(u↔v∣V∞)=p(∥xu−xv∥wu1/d+wv1/d∧1)αd




Goal 2 Prove


Power-law weights
Constant weights
Lower tail*:
If E[#edges of length n1/d]→∞
Main result: large deviations for the giant component
*log-corrections at phase transition
Upper tail:
If non-critical
*at continuity points of I(θ+ε)
Upper tail: polynomial decay when τ<∞

Related work:
- Sum of iid Par(τ): principle of single jump.
- Large deviations # edges En (vdHvdHKMM '24)
P(En>E[En]+nν)=∗(1+o(1))cνn−(τ−2)⌈ν/p⌉. - Inhomogeneous random graphs (J., Zwart '24+)
P(∣Cn(1)∣/n>ρ)=∗(1+o(1))Cρn−(τ−2)⌈h(ρ)⌉.
P(u↔v∣V∞)=p(∥xu−xv∥dwu1/d+wv1/d∧1)dα
Challenge: Capture dependency on percolation p



Power-law weights
Long-range percolation
Lower tail*:
If E[#edges of length n1/d]→∞
Main result: large deviations for the giant component
*log-corrections at phase transition
Upper tail:
If non-critical, ρ∈(θ,1)
*at continuity points of I(ρ)
Supercritical bond percolation on Zd

[Alexander, Chayes, Chayes '90; Cerf '00; Gandolfi '88; Grimmett & Marstrand '90, Kesten & Zhang '90, Pisztora '96]
Surface-tension driven behavior
The largest component

Lower tail large deviations of the giant*:
One decay exponent governing cluster sizes
*log(log)-corrections at non-unique maxima ζ
Small components*:
If E[#edges of length n1/d]→∞
If ζ>(d−1)/d

Thank you!

-
Cluster-size decay in supercritical long-range percolation;
With Júlia Komjáthy, Dieter Mitsche;
Electronic Journal of Probability (2024). -
Cluster-size decay in supercritical KSRGs;
With Júlia Komjáthy, Dieter Mitsche;
arXiv: 2303.00712, Annals of Probability (to appear). -
Large deviations of the giant in supercritical KSRGs;
With Júlia Komjáthy, Dieter Mitsche;
Preprint arXiv: 2404.02984.
Lower bounds: cluster-size decay
Aim: Find minimal ζ s.t.
Aim: Find γ s.t.
Lower bounds: cluster-size decay
Aim: Find minimal ζ s.t.
Aim: Find γ s.t.
Lower bounds: large deviations
(FKG)




Lower bounds: ∣Cn(2)∣
δ small
Upper bound: ∣Cn(2)∣









(Second-)largest component in supercritical spatial random graphs
- Cluster-size decay
- Second-largest component
Open problems:
-
Largest component:
- Linear in box size
- Law of large numbers
- Large deviations
Answered questions (d=1)
- Phase transition boundaries.
- Partial results d≥2
- Extension from PPP to grid
- Central limit theorem






- ζ∈[(d−1)/d,1)
Lower bounds
Upper bounds
Lower bounds
Upper bounds
Lower bounds
Upper bounds

Copy of Largest component in spatial random graphs
By joostjor
Copy of Largest component in spatial random graphs
- 106