3,673 research outputs found
Particle decay in false vacuum
We revisit the problem of decay of a metastable vacuum induced by the
presence of a particle. For the bosons of the `master field' the problem is
solved in any number of dimensions in terms of the spontaneous decay rate of
the false vacuum, while for a fermion we find a closed expression for the decay
rate in (1+1) dimensions. It is shown that in the (1+1) dimensional case an
infrared problem of one-loop correction to the decay rate of a boson is
resolved due to a cancellation between soft modes of the field. We also find
the boson decay rate in the `sine-Gordon staircase' model in the limits of
strong and weak coupling.Comment: 19 pages, 2 figure
Reconciling the X(3872) with the near-threshold enhancement in the D^0\bar{D}^{*0} final state
We investigate the enhancement in the D^0\bar{D}^0\pi^0 final state with the
mass M=3875.2\pm 0.7^{+0.3}_{-1.6}\pm 0.8 MeV found recently by the Belle
Collaboration in the B\to K D^0\bar{D}^0\pi^0 decay and test the possibility
that this is yet another manifestation of the well-established resonance
X(3872). We perform a combined Flatte analysis of the data for the
D^0\bar{D}^0\pi^0 mode, and for the \pi^+\pi^- J/\psi mode of the X(3872). Only
if the X(3872) is a virtual state in the D^0\bar{D}^{*0} channel, the data on
the new enhancement comply with those on the X(3872). In our fits, the mass
distribution in the D^0\bar{D}^{*0} mode exhibits a peak at 2-3 MeV above the
D^0\bar{D}^{*0} threshold, with a distinctive non-Breit-Wigner shape.Comment: RevTeX4, 17 pages, some references updated and corrected, version
published in Phys. Rev.
Three-body dynamics for the X(3872)
We investigate the role played by the three-body dynamics on
the near-threshold resonance X(3872) charmonium state, which is assumed to be
formed by nonperturbative dynamics. It is demonstrated that, as
compared to the naive static-pions approximation, the imaginary parts that
originate from the inclusion of dynamical pions reduce substantially the width
from the intermediate state. In particular, for a resonance
peaked at 0.5 MeV below the threshold, this contribution to
the width is reduced by about a factor of 2, and the effect of the pion
dynamics on the width grows as long as the resonance is shifted towards the
threshold. Although the physical width of the is
dominated by inelastic channels, our finding should still be of importance for
the line shapes in the channel below threshold.
For example, in the scattering length approximation, the imaginary part of the
scattering length includes effects of all the pion dynamics and does not only
stem from the width. Meanwhile, we find that another important quantity
for the phenomenology, the residue at the pole, is weakly sensitive to
dynamical pions. In particular, we find that the binding energy dependence of
this quantity from the full calculation is close to that found from a model
with pointlike interactions only, consistent with earlier claims.
Coupled-channel effects (inclusion of the charged channel) turn
out to have a moderate impact on the results.Comment: 34 pages, 6 figures, version to appear in Phys.Rev.
The decay eta_c^prime -> eta_c pi pi
It is pointed out that the decay of the recently observed charmonium
eta_c^prime resonance, eta_c^prime -> eta_c pi pi is simply related to the well
studied decay psi^prime -> J/psi pi pi and can thus be used for absolute
normalization of other decay modes of the eta_c^prime. The total rate of the
discussed decay should be approximately three to four times the corresponding
rate for the psi^prime$ resonance making the channel with charged pions the
most probable exclusive decay mode of the eta_c^prime with the branching ratio
in the range 5-10 %.Comment: 5 pages, references adde
Power Counting and Perturbative One Pion Exchange in Heavy Meson Molecules
We discuss the possible power counting schemes that can be applied in the
effective field theory description of heavy meson molecules, such as the
X(3872) or the recently discovered Zb(10610) and Zb(10650) states. We argue
that the effect of coupled channels is suppressed by at least two orders in the
effective field theory expansion, meaning that they can be safely ignored at
lowest order. The role of the one pion exchange potential between the heavy
mesons, and in particular the tensor force, is also analyzed. By using
techniques developed in atomic physics for handling power-law singular
potentials, which have been also successfully employed in nuclear physics, we
determine the range of center-of-mass momenta for which the tensor piece of the
one pion exchange potential is perturbative. In this momentum range, the one
pion exchange potential can be considered a subleading order correction,
leaving at lowest order a very simple effective field theory consisting only on
contact-range interactions.Comment: 21 pages, 1 figur
New bounds on the neutrino magnetic moment from the plasma induced neutrino chirality flip in a supernova
The neutrino chirality-flip process under the conditions of the supernova
core is investigated in detail with the plasma polarization effects in the
photon propagator taken into account, in a more consistent way than in earlier
publications. It is shown in part that the contribution of the proton fraction
of plasma is essential. New upper bounds on the neutrino magnetic moment are
obtained: mu_nu < (0.5 - 1.1) 10^{-12} mu_B from the limit on the supernova
core luminosity for nu_R emission, and mu_nu < (0.4 - 0.6) 10^{-12} mu_B from
the limit on the averaged time of the neutrino spin-flip. The best upper bound
on the neutrino magnetic moment from SN1987A is improved by the factor of 3 to
7.Comment: 19 pages, LaTeX, 7 EPS figures, submitted to Journal of Cosmology and
Astroparticle Physic
Dirac neutrino magnetic moment and the shock wave revival in a supernova explosion
The process of the two-step conversion of the neutrino helicity, , is analysed in the supernova conditions, where the first
stage is realized due to the interaction of the neutrino magnetic moment with
the plasma electrons and protons in the supernova core. The second stage is
caused by the neutrino resonant spin-flip in a magnetic field of the supernova
envelope. Given the neutrino magnetic moment within the interval , and with the existence of the
magnetic field at the scale G between the neutrinosphere and the
shock-wave stagnation region, it is shown that an additional energy of the
order of erg can be injected into this region during the typical time
of the shock-wave stagnation. This energy could be sufficient for stumulation
of the damped shock wave.Comment: 6 pages, LaTeX, 2 PS figures, based on the talk presented by N.V.
Mikheev at the XV International Seminar Quarks'2008, Sergiev Posad, Moscow
Region, May 23-29, 2008, to appear in the Proceeding
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