1,480 research outputs found
Why do investment banks buy put options from companies?
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordCompanies have collected billions in premiums from privately sold put options written on their
own stock. It is puzzling that counterparties, investment banks, would agree to make such transactions
with better-informed companies which have extraordinary ability to time the market as documented
by Jenter et al. (2011). To resolve this puzzle, we develop a model that shows that investment banks,
by offering to buy put options from better-informed parties, receive private information about issuing
companies. Our model also incorporates the practice of firms (such as Microsoft) of sometimes repurchasing their own put options and thus providing additional private information to investment banks.
Empirically, we find support for our theory from an abnormal 9% increase in the stock prices and a
40% increase in the trading volumes around the put sales. Examination of 13D filings reveals that
trading by upper management insiders cannot completely account for the change in volum
Multivariate discrimination and the Higgs + W/Z search
A systematic method for optimizing multivariate discriminants is developed
and applied to the important example of a light Higgs boson search at the
Tevatron and the LHC. The Significance Improvement Characteristic (SIC),
defined as the signal efficiency of a cut or multivariate discriminant divided
by the square root of the background efficiency, is shown to be an extremely
powerful visualization tool. SIC curves demonstrate numerical instabilities in
the multivariate discriminants, show convergence as the number of variables is
increased, and display the sensitivity to the optimal cut values. For our
application, we concentrate on Higgs boson production in association with a W
or Z boson with H -> bb and compare to the irreducible standard model
background, Z/W + bb. We explore thousands of experimentally motivated,
physically motivated, and unmotivated single variable discriminants. Along with
the standard kinematic variables, a number of new ones, such as twist, are
described which should have applicability to many processes. We find that some
single variables, such as the pull angle, are weak discriminants, but when
combined with others they provide important marginal improvement. We also find
that multiple Higgs boson-candidate mass measures, such as from mild and
aggressively trimmed jets, when combined may provide additional discriminating
power. Comparing the significance improvement from our variables to those used
in recent CDF and DZero searches, we find that a 10-20% improvement in
significance against Z/W + bb is possible. Our analysis also suggests that the
H + W/Z channel with H -> bb is also viable at the LHC, without requiring a
hard cut on the W/Z transverse momentum.Comment: 41 pages, 5 tables, 29 figure
The Yangian origin of the Grassmannian integral
In this paper we analyse formulas which reproduce different contributions to
scattering amplitudes in N=4 super Yang-Mills theory through a Grassmannian
integral. Recently their Yangian invariance has been proved directly by using
the explicit expression of the Yangian level-one generators. The specific
cyclic structure of the form integrated over the Grassmannian enters in a
crucial way in demonstrating the symmetry. Here we show that the Yangian
symmetry fixes this structure uniquely.Comment: 26 pages. v2: typos corrected, published versio
The mass area of jets
We introduce a new characteristic of jets called mass area. It is defined so
as to measure the susceptibility of the jet's mass to contamination from soft
background. The mass area is a close relative of the recently introduced
catchment area of jets. We define it also in two variants: passive and active.
As a preparatory step, we generalise the results for passive and active areas
of two-particle jets to the case where the two constituent particles have
arbitrary transverse momenta. As a main part of our study, we use the mass area
to analyse a range of modern jet algorithms acting on simple one and
two-particle systems. We find a whole variety of behaviours of passive and
active mass areas depending on the algorithm, relative hardness of particles or
their separation. We also study mass areas of jets from Monte Carlo simulations
as well as give an example of how the concept of mass area can be used to
correct jets for contamination from pileup. Our results show that the
information provided by the mass area can be very useful in a range of
jet-based analyses.Comment: 36 pages, 12 figures; v2: improved quality of two plots, added entry
in acknowledgments, nicer form of formulae in appendix A; v3: added section
with MC study and pileup correction, version accepted by JHE
The Grassmannian and the Twistor String: Connecting All Trees in N=4 SYM
We present a new, explicit formula for all tree-level amplitudes in N=4 super
Yang-Mills. The formula is written as a certain contour integral of the
connected prescription of Witten's twistor string, expressed in link variables.
A very simple deformation of the integrand gives directly the Grassmannian
integrand proposed by Arkani-Hamed et al. together with the explicit contour of
integration. The integral is derived by iteratively adding particles to the
Grassmannian integral, one particle at a time, and makes manifest both parity
and soft limits. The formula is shown to be related to those given by Dolan and
Goddard, and generalizes the results of earlier work for NMHV and N^2MHV to all
N^(k-2)MHV tree amplitudes in N=4 super Yang-Mills.Comment: 26 page
Optimal jet radius in kinematic dijet reconstruction
Obtaining a good momentum reconstruction of a jet is a compromise between
taking it large enough to catch the perturbative final-state radiation and
small enough to avoid too much contamination from the underlying event and
initial-state radiation. In this paper, we compute analytically the optimal jet
radius for dijet reconstructions and study its scale dependence. We also
compare our results with previous Monte-Carlo studies.Comment: 30 pages, 11 figures; minor corrections; published in JHE
Primary aldosteronism: A Japanese perspective
Primary aldosteronism (PA) is the most common cause of secondary hypertension, accounting for 10% of all hypertension. Far from being benign, hypertension due to PA is associated with high cardiovascular morbidity and mortality. However, PA is still underdiagnosed in general practice. Recent reports strongly recommend that identifying patients with PA is cost-beneficial based on improved cardiovascular outcomes afforded by specific surgical and medical treatment. This review provides an update of PA including controversial aspects of diagnosis and treatment
Challenges to the development of antigen-specific breast cancer vaccines
Continued progress in the development of antigen-specific breast cancer vaccines depends on the identification of appropriate target antigens, the establishment of effective immunization strategies, and the ability to circumvent immune escape mechanisms. Methods such as T cell epitope cloning and serological expression cloning (SEREX) have led to the identification of a number target antigens expressed in breast cancer. Improved immunization strategies, such as using dendritic cells to present tumor-associated antigens to T lymphocytes, have been shown to induce antigen-specific T cell responses in vivo and, in some cases, objective clinical responses. An outcome of successful tumor immunity is the evolution of antigen-loss tumor variants. The development of a polyvalent breast cancer vaccine, directed against a panel of tumor-associated antigens, may counteract this form of immune escape
Resummation of heavy jet mass and comparison to LEP data
The heavy jet mass distribution in e+e- collisions is computed to
next-to-next-to-next-to leading logarithmic (NNNLL) and next-to-next-to leading
fixed order accuracy (NNLO). The singular terms predicted from the resummed
distribution are confirmed by the fixed order distributions allowing a precise
extraction of the unknown soft function coefficients. A number of quantitative
and qualitative comparisons of heavy jet mass and the related thrust
distribution are made. From fitting to ALEPH data, a value of alpha_s is
extracted, alpha_s(m_Z)=0.1220 +/- 0.0031, which is larger than, but not in
conflict with, the corresponding value for thrust. A weighted average of the
two produces alpha_s(m_Z) = 0.1193 +/- 0.0027, consistent with the world
average. A study of the non-perturbative corrections shows that the flat
direction observed for thrust between alpha_s and a simple non-perturbative
shape parameter is not lifted in combining with heavy jet mass. The Monte Carlo
treatment of hadronization gives qualitatively different results for thrust and
heavy jet mass, and we conclude that it cannot be trusted to add power
corrections to the event shape distributions at this accuracy. Whether a more
sophisticated effective field theory approach to power corrections can
reconcile the thrust and heavy jet mass distributions remains an open question.Comment: 33 pages, 14 figures. v2 added effect of lower numerical cutoff with
improved extraction of the soft function constants; power correction
discussion clarified. v3 small typos correcte
Local Spacetime Physics from the Grassmannian
A duality has recently been conjectured between all leading singularities of
n-particle N^(k-2)MHV scattering amplitudes in N=4 SYM and the residues of a
contour integral with a natural measure over the Grassmannian G(k,n). In this
note we show that a simple contour deformation converts the sum of Grassmannian
residues associated with the BCFW expansion of NMHV tree amplitudes to the CSW
expansion of the same amplitude. We propose that for general k the same
deformation yields the (k-2) parameter Risager expansion. We establish this
equivalence for all MHV-bar amplitudes and show that the Risager degrees of
freedom are non-trivially determined by the GL(k-2) "gauge" degrees of freedom
in the Grassmannian. The Risager expansion is known to recursively construct
the CSW expansion for all tree amplitudes, and given that the CSW expansion
follows directly from the (super) Yang-Mills Lagrangian in light-cone gauge,
this contour deformation allows us to directly see the emergence of local
space-time physics from the Grassmannian.Comment: 22 pages, 13 figures; v2: minor updates, typos correcte
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