1,079 research outputs found
A simple remark on a flat projective morphism with a Calabi-Yau fiber
If a K3 surface is a fiber of a flat projective morphisms over a connected
noetherian scheme over the complex number field, then any smooth connected
fiber is also a K3 surface. Observing this, Professor Nam-Hoon Lee asked if the
same is true for higher dimensional Calabi-Yau fibers. We shall give an
explicit negative answer to his question as well as a proof of his initial
observation.Comment: 8 pages, main theorem is generalized, one more remark is added,
mis-calculation and typos are corrected etc
A high fibered power of a family of varieties of general type dominates a variety of general type
We prove the following theorem:
Fibered Power Theorem: Let X\rar B be a smooth family of positive
dimensional varieties of general type, with irreducible. Then there exists
an integer , a positive dimensional variety of general type , and a
dominant rational map X^n_B \das W_n.Comment: Latex2e (in latex 2.09 compatibility mode). To get a fun-free version
change the `FUN' variable to `n' on the second line (option dedicated to my
friend Yuri Tschinkel). Postscript file with color illustration available on
http://math.bu.edu/INDIVIDUAL/abrmovic/fibered.p
Five-Dimensional Supersymmetric Gauge Theories and Degenerations of Calabi-Yau Spaces
We discuss five-dimensional supersymmetric gauge theories. An anomaly renders
some theories inconsistent and others consistent only upon including a
Wess-Zumino type Chern-Simons term. We discuss some necessary conditions for
existence of nontrivial renormalization group fixed points and find all
possible gauge groups and matter content which satisfy them. In some cases, the
existence of these fixed points can be inferred from string duality
considerations. In other cases, they arise from M-theory on Calabi-Yau
threefolds. We explore connections between aspects of the gauge theory and
Calabi-Yau geometry. A consequence of our classification of field theories with
nontrivial fixed points is a fairly complete classification of a class of
singularities of Calabi-Yau threefolds which generalize the ``del Pezzo
contractions'' and occur at higher codimension walls of the K\"{a}hler cone.Comment: harvmac, 52 pp., 5 figures (reference added
Anti-Pluricanonical Systems On Q-Fano Threefolds
We investigate birationality of the anti-pluricanonical map , the
rational map defined by the anti-pluricanonical system , on
-Fano threefolds.Comment: 18 page
Defect and Hodge numbers of hypersurfaces
We define defect for hypersurfaces with A-D-E singularities in complex
projective normal Cohen-Macaulay fourfolds having some vanishing properties of
Bott-type and prove formulae for Hodge numbers of big resolutions of such
hypersurfaces. We compute Hodge numbers of Calabi-Yau manifolds obtained as
small resolutions of cuspidal triple sextics and double octics with higher A_j
singularities.Comment: 25 page
Three embeddings of the Klein simple group into the Cremona group of rank three
We study the action of the Klein simple group G consisting of 168 elements on
two rational threefolds: the three-dimensional projective space and a smooth
Fano threefold X of anticanonical degree 22 and index 1. We show that the
Cremona group of rank three has at least three non-conjugate subgroups
isomorphic to G. As a by-product, we prove that X admits a Kahler-Einstein
metric, and we construct a smooth polarized K3 surface of degree 22 with an
action of the group G.Comment: 43 page
Homological Type of Geometric Transitions
The present paper gives an account and quantifies the change in topology
induced by small and type II geometric transitions, by introducing the notion
of the \emph{homological type} of a geometric transition. The obtained results
agree with, and go further than, most results and estimates, given to date by
several authors, both in mathematical and physical literature.Comment: 36 pages. Minor changes: A reference and a related comment in Remark
3.2 were added. This is the final version accepted for publication in the
journal Geometriae Dedicat
The Frontier Fields Lens Modeling Comparison Project
Gravitational lensing by clusters of galaxies offers a powerful probe of
their structure and mass distribution. Deriving a lens magnification map for a
galaxy cluster is a classic inversion problem and many methods have been
developed over the past two decades to solve it. Several research groups have
developed techniques independently to map the predominantly dark matter
distribution in cluster lenses. While these methods have all provided
remarkably high precision mass maps, particularly with exquisite imaging data
from the Hubble Space Telescope (HST), the reconstructions themselves have
never been directly compared. In this paper, we report the results of comparing
various independent lens modeling techniques employed by individual research
groups in the community. Here we present for the first time a detailed and
robust comparison of methodologies for fidelity, accuracy and precision. For
this collaborative exercise, the lens modeling community was provided simulated
cluster images -- of two clusters Ares and Hera -- that mimic the depth and
resolution of the ongoing HST Frontier Fields. The results of the submitted
reconstructions with the un-blinded true mass profile of these two clusters are
presented here. Parametric, free-form and hybrid techniques have been deployed
by the participating groups and we detail the strengths and trade-offs in
accuracy and systematics that arise for each methodology. We note in conclusion
that lensing reconstruction methods produce reliable mass distributions that
enable the use of clusters as extremely valuable astrophysical laboratories and
cosmological probes.Comment: 38 pages, 25 figures, submitted to MNRAS, version with full
resolution images can be found at
http://pico.bo.astro.it/~massimo/papers/FFsims.pd
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