20,638 research outputs found
Risk Premiums and the Storage of Agricultural Commodities
The existence of a commodity market risk premium has attracted the interest of researchers for several decades. Most attempts to measure risk premiums have been focused on futures markets. However, if the risk premium is a payment made by hedgers (as suggested by Keynes) to reduce their risk profile, then the risk being reduced originates in the cash market. This suggests that the risk premium may also originate in the cash market. As such, the search for a risk premium should focus on the cash market, and, given Working's Supply of Storage Curve, should be measured as a function of stored inventory. This paper develops an expected utility based model that separates the risk premium from other storage incentives, and illustrates the role of the cash market risk premium on the storage decisions of two different market agents.
Mass spectra of Zc and Zb exotic states as hadron molecules
We construct charmonium-like and bottomonium-like molecular interpolating
currents with quantum numbers J(PC)=1(+-) in a systematic way, including both
color singlet-singlet and color octet-octet structures. Using these
interpolating currents, we calculate two-point correlation functions and
perform QCD sum rule analyses to obtain mass spectra of the charmonium-like and
bottomonium-like molecular states. Masses of the charmonium-like q_bar c c_bar
q molecular states for these various currents are extracted in the range
3.85-4.22 GeV, which are in good agreement with observed masses of the Zc
resonances. Our numerical results suggest a possible landscape of hadronic
molecule interpretations of the newly-observed Zc states. Mass spectra of the
bottomonium-like q_bar b b_bar q molecular states are similarly obtained in the
range 9.92-10.48 GeV, which support the interpretation of the Zb(10610) meson
as a molecular state within theoretical uncertainties. Possible decay channels
of these molecular states are also discussed.Comment: 15 pages, 3 figures, 2 tables, accepted by PR
Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3
The dielectric constant of the incipient ferroelectric EuTiO exhibits a
sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering
of the Eu spins simultaneously appears, indicating coupling between the
magnetism and dielectric properties. This may be attributed to the modification
of the soft-phonon mode, , which is the main contribution to the
large dielectric constant, by the Eu spins(7 per Eu). By adding the
coupling term between the magnetic and electrical subsystems as we show that the variation of the frequency of
soft-phonon mode depends on the spin correlation between the nearest neighbors
Eu spins and is substantially changed under a magnetic field.Comment: 13 pages, 4 figure
Variational Monte-Carlo studies of Gossamer Superconductivity
We use a partially Gutzwiller projected BCS d-wave wavefunction with an
antiferromagentic weighting factor to study the ground state phase diagram of a
half filled Hubbard-Heisenberg model in a square lattice with nearest neighbor
hopping and a diagonal hopping . The calculations are carried out by
using variational Monte Carlo method which treats the Gutzwiller projection
explicitly. At large on-site Coulomb interaction , the ground state is
antiferromagnetic. As decreases, the ground state becomes superconducting
and eventually metallic. The phase diagram is obtained by extensive
calculations. As compared to the strong effect of , the phase boundaries
turn out to be less sensitive to . The result is consistent with the
phase diagram in layered organic conductors, and is compared to the earlier
mean field result based on the Gutzwiller approximation.Comment: 5 pages, 4 figure
Doubly hidden-charm/bottom tetraquark states
We study the mass spectra for the and
tetraquark states by developing a moment sum rule method. Our results show that
the tetraquarks lie below the threshold of
. They are probably stable and very narrow. The masses
for the doubly hidden-charm states are higher than the
spontaneous dissociation thresholds of two charmonium mesons. We suggest to
search for such states in the and
channels.Comment: 8 pages, 2 figures. More references added. Conference proceedings for
6th International Conference on New Frontiers in Physics (ICNFP 2017), Crete,
Greece, 17-29 Aug, 201
Origin of the X-ray Quasi-Periodic Oscillations and Identification of a Transient Ultraluminous X-Ray Source in M82
The starburst galaxy M82 contains two ultraluminous X-ray sources (ULXs),
CXOM82 J095550.2+694047 (=X41.4+60) and CXOM82 J095551.1+694045 (=X42.3+59),
which are unresolved by XMM-Newton. We revisited the two XMM-Newton
observations of M82 and analyzed the surface brightness profiles using the
known Chandra source positions. We show that the quasi-periodic oscillations
(QPOs) detected with XMM-Newton originate from X41.4+60, the brightest X-ray
source in M82. Correcting for the contributions of the unresolved sources, the
QPO at a frequency of 55.8+/-1.3 mHz on 2001 May 06 had a fractional rms
amplitude of 32%, and the QPO at 112.9+/-1.3 mHz on 2004 April 21 had an
amplitude of 21%. The QPO frequency may possibly be correlated with the source
flux, similar to the type C QPOs in XTE 1550-564 and GRS 1915+105, but at
luminosities two orders of magnitude higher. X42.3+59, the second brightest
source in M82, displayed a strikingly high flux of 1.4E-11 ergs/cm^2/s in the
2-10 keV band on 2001 May 6. A seven-year light curve of X42.3+59 shows extreme
variability over a factor of 1000; the source is not detected in several
Chandra observations. This transient behavior suggests accretion from an
unstable disk. If the companion star is massive, as might be expected in the
young stellar environment, then the compact object would likely be an IMBH.Comment: 9 pages, 6 figures, submitted to ApJ on May 08, 200
Open-flavor charmed/bottom and tetraquark states
We provide comprehensive investigations for the mass spectrum of exotic
open-flavor charmed/bottom , , , tetraquark states with various spin-parity assignments
and in the framework of QCD sum rules. In the
diquark configuration, we construct the diquark-antidiquark interpolating
tetraquark currents using the color-antisymmetric scalar and axial-vector
diquark fields. The stable mass sum rules are established in reasonable
parameter working ranges, which are used to give reliable mass predictions for
these tetraquark states. We obtain the mass spectra for the open-flavor
charmed/bottom , , , tetraquark states with various spin-parity quantum numbers. In
addition, we suggest searching for exotic doubly-charged tetraquarks, such as
in future experiments at facilities
such as BESIII, BelleII, PANDA, LHCb and CMS, etc.Comment: 19 pages, 4 figures, 5 tables, accepted by Phys. Rev. D (in press
- …