17,885 research outputs found
Y(4260) and Y(4360) as mixed hadrocharmonium
Recent BESIII data indicate a significant rate of the process at the Y(4260) and Y(4360) resonances, implying a substantial
breaking of the heavy quark spin symmetry. We consider these resonances within
the picture of hadrocharmonium, i.e. of (relatively) compact charmonium
embedded in a light quark mesonic excitation. We suggest that the resonances
Y(4260) and Y(4360) are a mixture, with mixing close to maximal, of two states
of hadrochamonium, one containing a spin-triplet pair and the other
containing a spin-singlet heavy quark pair. We argue that this model is in a
reasonable agreement with the available data and produces distinctive and
verifiable predictions for the energy dependence of the production rate in
annihilation of the final states , and
, including the pattern of interference between the two
resonances.Comment: 9 pages, 2 figures. Note added including a comparison of our model
with the new BESIII data which became available after the initial version of
our pape
Suppression of the S-wave production of (3/2)^+ + (1/2)^- heavy meson pairs in e^+e^- annihilation
The heavy meson-antimeson pairs, where one is an excited meson and the other is a ground state meson, namely the pairs ( + c.c.), (
+ c.c.), ( + c.c.) in the charm sector and ( + c.c.), ( + c.c.), ( + c.c.) in the
bottom sector, are allowed, by the quantum numbers, to be produced in the
wave in annihilation. We show, however, that such -wave production
is forbidden by the heavy quark spin symmetry. Thus the yield of the considered
meson pairs in annihilation should be significantly suppressed near
the respective thresholds. In our view, this substantially weakens the
arguments for considering the Y(4260) charmonium-like resonance as a molecular state.Comment: 6 pages, 1 figur
Sandpiles and unicycles on random planar maps
We consider the abelian sandpile model and the uniform spanning unicycle on
random planar maps. We show that the sandpile density converges to 5/2 as the
maps get large. For the spanning unicycle, we show that the length and area of
the cycle converges to the hitting time and location of a simple random walk in
the first quadrant. The calculations use the "hamburger-cheeseburger"
construction of Fortuin--Kasteleyn random cluster configurations on random
planar maps.Comment: 12 pages. Section 3 is shorte
Energy-Efficient Resource Allocation in Time Division Multiple-Access over Fading Channels
We investigate energy-efficiency issues and resource allocation policies for
time division multi-access (TDMA) over fading channels in the power-limited
regime. Supposing that the channels are frequency-flat block-fading and
transmitters have full or quantized channel state information (CSI), we first
minimize power under a weighted sum-rate constraint and show that the optimal
rate and time allocation policies can be obtained by water-filling over
realizations of convex envelopes of the minima for cost-reward functions. We
then address a related minimization under individual rate constraints and
derive the optimal allocation policies via greedy water-filling. Using
water-filling across frequencies and fading states, we also extend our results
to frequency-selective channels. Our approaches not only provide fundamental
power limits when each user can support an infinite number of
capacity-achieving codebooks, but also yield guidelines for practical designs
where users can only support a finite number of adaptive modulation and coding
(AMC) modes with prescribed symbol error probabilities, and also for systems
where only discrete-time allocations are allowed.Comment: 45 pages, 9 figures, submitted to IEEE Transactions on Information
Theor
production in annihilation through
We argue that the recent BESIII data on the cross section for the process
in the center of mass energy range 4.21 - 4.42
GeV can be described by the contribution of the known charmonium-like resonance
with the mass of about 4190\,MeV. The value of the coupling in the
transition needed for this mechanism is
comparable to that in another known similar transition . The suggested mechanism also naturally explains the reported
relative small value of the cross section for the final states and above their respective thresholds.Comment: 6 page
Remarks on double Higgs boson production by gluon fusion at threshold
The amplitude of double Higgs boson production by the gluon fusion, , is known to be small due to cancellation between the graphs with the boson
trilinear coupling and those with the coupling to the top quark. For this
reason a study of this process was suggested as a sensitive probe of the Higgs
sector nonlinearity. We calculate in a closed analytical form this amplitude at
the threshold of the two bosons, where the cancellation is the strongest, and
discuss the origin of the small value of the amplitude. We also note that the
cancellation in the double boson production is in fact a part of a more general
phenomenon of suppression of similar threshold amplitudes for multiple boson
production, which, although not directly relevant to the actual top quark and
the Higgs boson, can be useful in other studies.Comment: 9 pages, 3 figure
as a bound state
We suggest that the observed properties of the charmoniumlike resonance
can possibly be explained if it is an wave molecular bound state
of meson pair with binding energy about 18\,MeV. In particular,
the decays of to pairs of non-strange mesons are suppressed and
proceed at a rate comparable to that of the decay ,
whose branching fraction can be as large as about 0.3. Other major types of
decay of with a comparable (or slightly smaller) rate are the
transition and the decays into light hadrons due to
the annihilation of the quark pair. The existence of a bound state
should lead to an enhancement in the spectrum of the invariant mass for the
near threshold in decays, e.g. in
which enhancement can be tested experimentally.Comment: 8 page
Metastable vacuum decay in center-stabilized Yang-Mills theory at large N
We calculate the rate of the decay of a metastable vacuum state in
gauge theory on space with a double trace
deformation suggested by \"Unsal and Yaffe. The derived analytical expression
for the exponential factor in the decay rate, including the dependence on the
parameter , gives the exact behavior in the leading power of in the
limit of large and provides a better approximation than a recently found in
the literature numerical result.Comment: 8 pages, 1 figur
Mixing of partial waves near threshold in annihilation
We consider the production of meson pairs in
annihilation near the threshold. The rescattering due to pion exchange between
the mesons results in a mixing between three partial wave amplitudes: two
-wave with the total spin of the meson pair S=0 and S=2 and an F-wave
amplitude. The mixing due to pion exchange with a low momentum transfer is
calculable up to c.m. energy \,MeV above the threshold.
We find that the mixing is numerically quite small in this energy range,
while the mixing of the two P-wave amplitudes is rapidly changing with energy
and can reach of order one at such low energies.Comment: 8 pages, 3 figure
Isospin violation in the yield of S-wave heavy meson pairs near threshold
We consider production of overall neutral pairs consisting of heavy
or meson and antimeson in the processes, where the pair can be
created in an -wave, such as and
, and similar reactions with
mesons. The ratio of the yield of pairs of charged mesons
to that of neutral mesons near the threshold for the heavy pair is strongly
affected by the isospin breaking due to the isotopic mass differences and due
to the Coulomb interaction between the charged mesons. The actual behavior of
the isospin breaking in is also sensitive to the strong interaction
between the heavy mesons, so that experimental measurement of this ratio can be
used as a probe of this strong interaction. We calculate at and very
near the threshold in terms of the isotopic scattering lengths for the meson
pairs. In particular we find that the yield of pairs of charged mesons does not
go to zero at exactly the threshold, but rather starts with a finite step,
whose height depends on the value of the scattering length in a particular
channel.Comment: 10 pages, 2 figure
- β¦