343 research outputs found
Exact Post-Selection Inference for Sequential Regression Procedures
We propose new inference tools for forward stepwise regression, least angle
regression, and the lasso. Assuming a Gaussian model for the observation vector
y, we first describe a general scheme to perform valid inference after any
selection event that can be characterized as y falling into a polyhedral set.
This framework allows us to derive conditional (post-selection) hypothesis
tests at any step of forward stepwise or least angle regression, or any step
along the lasso regularization path, because, as it turns out, selection events
for these procedures can be expressed as polyhedral constraints on y. The
p-values associated with these tests are exactly uniform under the null
distribution, in finite samples, yielding exact type I error control. The tests
can also be inverted to produce confidence intervals for appropriate underlying
regression parameters. The R package "selectiveInference", freely available on
the CRAN repository, implements the new inference tools described in this
paper.Comment: 26 pages, 5 figure
Hidden exceptional symmetry in the pure spinor superstring
The pure spinor formulation of superstring theory includes an interacting
sector of central charge , which can be realized as a curved
system on the cone over the orthogonal Grassmannian
. We find that the spectrum of the system
organizes into representations of the affine
algebra at level , whose subalgebra encodes the rotational and ghost symmetries of the
system. As a consequence, the pure spinor partition function decomposes as a
sum of affine characters. We interpret this as an instance of
a more general pattern of enhancements in curved systems, which
also includes the cases and ,
corresponding to target spaces that are cones over the complex Grassmannian
and the complex Cayley plane . We identify
these curved systems with the chiral algebras of certain
CFTs arising from twisted compactification of 4d SCFTs
on .Comment: 8 pages, 1 figure; v2: added references, minor update
HST/WFC3 Observations of an Off-Nuclear Superbubble in Arp 220
We present a high spatial resolution optical and infrared study of the
circumnuclear region in Arp 220, a late-stage galaxy merger. Narrowband imaging
using HST/WFC3 has resolved the previously observed peak in H+[NII]
emission into a bubble-shaped feature. This feature measures 1.6" in diameter,
or 600 pc, and is only 1" northwest of the western nucleus. The bubble is
aligned with the western nucleus and the large-scale outflow axis seen in
X-rays. We explore several possibilities for the bubble origin, including a jet
or outflow from a hidden active galactic nucleus (AGN), outflows from high
levels of star formation within the few hundred pc nuclear gas disk, or an
ultraluminous X-ray source. An obscured AGN or high levels of star formation
within the inner 100 pc of the nuclei are favored based on the alignment
of the bubble and energetics arguments.Comment: Accepted for publication in ApJ. 12 pages, 10 figure
- …