8,022 research outputs found

### Cooperative three- and four- player quantum games

A cooperative multi-player quantum game played by 3 and 4 players has been
studied. Quantum superposed operator is introduced in this work which solves
the non-zero sum difficulty in previous treatment. The role of quantum
entanglement of the initial state is discussed in details.Comment: 7 pages with 3 figures. To appear in Physics Letters

### Radiative and leptonic decays of the pseudoscalar charmonium state $\eta_c$

The radiative and leptonic decays of $\eta_c\to \gamma\gamma$ and $\eta_c\to
l^+l^-$ are studied. For $\eta_c\to \gamma\gamma$ decay, the second-order
electromagnetic tree-level diagram gives the leading contribution. The decay
rate of $\eta_c\to \gamma\gamma$ is calculated, the prediction is in good
agreement with the experimental data. For \eta_c\to l^+\l^-, both the tree
and loop diagrams are calculated. The analysis shows that the loop contribution
dominates, the contribution of tree diagram with $Z^0$ intermediate state can
only modifies the decay rate by less than 1%. The prediction of the branching
ratios of $\eta_c\to e^+e^-$ and $\mu^+\mu^-$ are very tiny within the standard
model. The smallness of these predictions within the standard model makes the
leptonic decays of $\eta_c$ sensitive to physics beyond the standard model.
Measurement of the leptonic decay may give information of new physics.Comment: 9 pages, 4 figures, RevTex, small change, version to appear in Phys.
Rev.

### Bochner Laplacian and Bergman kernel expansion of semi-positive line bundles on a Riemann surface

We generalize the results of Montgomery for the Bochner Laplacian on high
tensor powers of a line bundle. When specialized to Riemann surfaces, this
leads to the Bergman kernel expansion and geometric quantization results for
semi-positive line bundles whose curvature vanishes at finite order. The proof
exploits the relation of the Bochner Laplacian on tensor powers with the
sub-Riemannian (sR) Laplacian

### Gravitational Stability and Screening Effect from D Extra Timelike Dimensions

We study (3+1)+D dimensional spacetime, where D extra dimensions are
timelike. Compactification of the D timelike dimensions leads to tachyonic
Kaluza-Klein gravitons. We calculate the gravitational self-energies of massive
spherical bodies due to the tachyonic exchange, discuss their stability, and
find that the gravitational force is screened in a certain number of the extra
dimensions. We also derive the exact relationship between the Newton constants
in the full 4+D dimensional spacetime with the D extra times and the ordinary
Newton constant of our 4 dimensional world.Comment: harvmac, 20 pages, typos corrected, refs. added and correcte

### TeV-Scale Stringy Signatures at the Electron-positron Collider

We investigate the TeV-scale stringy signals of the four-fermion scattering
at the electron-positron collider with the center of mass energy 500-1000 GeV.
The nature of the stringy couplings leads to distinguishable asymmetries
comparing to the other new physics models. Specifically, the stringy states in
the four-fermion scattering at the leading-order corrections are of spin-1 and
2 with the chiral couplings inherited from the gauge bosons identified as the
zeroth-mode string states. The angular left-right, forward-backward,
center-edge asymmetries and the corresponding polarized-beam asymmetries are
investigated. The low-energy stringy corrections are compared to the ones
induced by the Kaluza-Klein (KK) gravitons. The angular left-right asymmetry of
the scattering with the final states of u and d-type quarks, namely c and b,
shows significant deviations from the Standard Model values. The center-edge
and forward-backward asymmetries for all final-states fermions also show
significant deviations from the corresponding Standard Model values. The
differences between the signatures induced by the stringy corrections and the
KK gravitons are appreciable in both angular left-right and forward-backward
asymmetries.Comment: 22 pages,8 figures, expanded content, added reference

### Financial Connections and Systemic Risk

We develop a model where institutions form connections through swaps of projects in order to diversify their individual risk. These connections lead to two different network structures. In a clustered network groups of financial institutions hold identical portfolios and default together. In an unclustered network defaults are more dispersed. With long term finance welfare is the same in both networks. In contrast, when short term finance is used, the network structure matters. Upon the arrival of a signal about banksâ€™ future defaults, investors update their expectations of bank solvency. If their expectations are low, they do not roll over the debt and there is systemic risk in that all institutions are early liquidated. We compare investorsâ€™ rollover decisions and welfare in the two networks.http://cadmus.eui.eu/bitstream/handle/1814/14256/ECO_2010_30.pdf?sequence=1

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