Universality of the likelihood-ratio statistic under stable finite-order VAR dynamics

Fix kNk\in\mathbb{N} and C>0C>0. Suppose that the data-generating process satisfies

ΔXt=μ+i=1k1ΓiΔXti+εt,t=1,,T,\Delta X_t=\mu+\sum_{i=1}^{k-1}\Gamma_i\Delta X_{t-i}+\varepsilon_t,\qquad t=1,\ldots,T,

where the innovations are independent and identically distributed as N(0,Λ)\mathcal{N}(0,\Lambda), the covariance matrix satisfies Λ2<C\|\Lambda\|_2<C and Λ12<C\|\Lambda^{-1}\|_2<C, Γi2<C\|\Gamma_i\|_2<C and rank(Γi)<C\operatorname{rank}(\Gamma_i)<C for 1ik11\leq i\leq k-1, all roots of

det(1Ni=1k1Γizi)=0\det\left(\mathbf{1}_N-\sum_{i=1}^{k-1}\Gamma_i z^i\right)=0

are such that z>1+C1|z|>1+C^{-1}, and ΓjΔX1i2C\|\Gamma_j\Delta X_{1-i}\|_2\leq C and ΓjμC\|\Gamma_j\mu\|\leq C for 1i,jk11\leq i,j\leq k-1. Universality conjecture. As T,NT,N\to\infty with T/N[k+1+C1,C]T/N\in[k+1+C^{-1},C], the conclusion of Theorem J continues to hold with the same centering and scaling constants c1(N,T)c_1(N,T) and c2(N,T)c_2(N,T):

i=1rln(1λ~i)rc1(N,T)N2/3c2(N,T)T,Ndi=1rai.\frac{\sum_{i=1}^{r}\ln(1-\tilde{\lambda}_i)-r\,c_1(N,T)}{N^{-2/3}c_2(N,T)}\xrightarrow[T,N\to\infty]{d}\sum_{i=1}^{r}\mathfrak{a}_i.

This extends the asserted asymptotics beyond the null model to stable finite-order vector autoregressions with bounded coefficient ranks and covariance conditioning. The supplied text does not identify whether this conjecture is proved or remains open.

Sources & referencesView supporting material

Primary source

Anna Bykhovskaya and Vadim Gorin, “Asymptotics of Cointegration Tests for High-Dimensional VAR(k)”, arXiv:2202.07150 (2023).

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