41 research outputs found
Small amplitude quasi-breathers and oscillons
Quasi-breathers (QB) are time-periodic solutions with weak spatial
localization introduced in G. Fodor et al. in Phys. Rev. D. 74, 124003 (2006).
QB's provide a simple description of oscillons (very long-living spatially
localized time dependent solutions). The small amplitude limit of QB's is
worked out in a large class of scalar theories with a general self-interaction
potential, in spatial dimensions. It is shown that the problem of small
amplitude QB's is reduced to a universal elliptic partial differential
equation. It is also found that there is the critical dimension, ,
above which no small amplitude QB's exist. The QB's obtained this way are shown
to provide very good initial data for oscillons. Thus these QB's provide the
solution of the complicated, nonlinear time dependent problem of small
amplitude oscillons in scalar theories.Comment: 24 pages, 19 figure
Computation of the radiation amplitude of oscillons
The radiation loss of small amplitude oscillons (very long-living, spatially
localized, time dependent solutions) in one dimensional scalar field theories
is computed in the small-amplitude expansion analytically using matched
asymptotic series expansions and Borel summation. The amplitude of the
radiation is beyond all orders in perturbation theory and the method used has
been developed by Segur and Kruskal in Phys. Rev. Lett. 58, 747 (1987). Our
results are in good agreement with those of long time numerical simulations of
oscillons.Comment: 22 pages, 9 figure
Mass loss and longevity of gravitationally bound oscillating scalar lumps (oscillatons) in D-dimensions
Spherically symmetric oscillatons (also referred to as oscillating soliton
stars) i.e. gravitationally bound oscillating scalar lumps are considered in
theories containing a massive self-interacting real scalar field coupled to
Einstein's gravity in 1+D dimensional spacetimes. Oscillations are known to
decay by emitting scalar radiation with a characteristic time scale which is,
however, extremely long, it can be comparable even to the lifetime of our
universe. In the limit when the central density (or amplitude) of the
oscillaton tends to zero (small-amplitude limit) a method is introduced to
compute the transcendentally small amplitude of the outgoing waves. The results
are illustrated in detail on the simplest case, a single massive free scalar
field coupled to gravity.Comment: 23 pages, 2 figures, references on oscillons added, version to appear
in Phys. Rev.
Boson stars and oscillatons in an inflationary universe
Spherically symmetric gravitationally bound, oscillating scalar lumps (boson
stars and oscillatons) are considered in Einstein's gravity coupled to massive
scalar fields in 1+D dimensional de Sitter-type inflationary space-times. We
show that due to inflation bosons stars and oscillatons lose mass through
scalar radiation, but at a rate that is exponentially small when the expansion
rate is slow.Comment: 19 pages, 5 figure
On decay of large amplitude bubble of disoriented chiral condensate
The time evolution of initially formed large amplitude bubble of disoriented
chiral condensate (DCC) is studied. It is found that the evolution of this
object may have a relatively long pre-decay stage. Simple explanation of such
delay of the DCC bubble decay is given. This delay is related to the existence
of the approximate solutions of multi-soliton type of the corresponding radial
sine-Gordon equation in (3+1) dimensions at large bubble radius.Comment: 6 pages, LaTeX, 5 PostScript figure
Numerical simulation of oscillatons: extracting the radiating tail
Spherically symmetric, time-periodic oscillatons -- solutions of the
Einstein-Klein-Gordon system (a massive scalar field coupled to gravity) with a
spatially localized core -- are investigated by very precise numerical
techniques based on spectral methods. In particular the amplitude of their
standing-wave tail is determined. It is found that the amplitude of the
oscillating tail is very small, but non-vanishing for the range of frequencies
considered. It follows that exactly time-periodic oscillatons are not truly
localized, and they can be pictured loosely as consisting of a well
(exponentially) localized nonsingular core and an oscillating tail making the
total mass infinite. Finite mass physical oscillatons with a well localized
core -- solutions of the Cauchy-problem with suitable initial conditions -- are
only approximately time-periodic. They are continuously losing their mass
because the scalar field radiates to infinity. Their core and radiative tail is
well approximated by that of time-periodic oscillatons. Moreover the mass loss
rate of physical oscillatons is estimated from the numerical data and a
semi-empirical formula is deduced. The numerical results are in agreement with
those obtained analytically in the limit of small amplitude time-periodic
oscillatons.Comment: 22 figures, accepted for publication in PR
Oscillons in dilaton-scalar theories
It is shown by both analytical methods and numerical simulations that
extremely long living spherically symmetric oscillons appear in virtually any
real scalar field theory coupled to a massless dilaton (DS theories). In fact
such "dilatonic" oscillons are already present in the simplest non-trivial DS
theory -- a free massive scalar field coupled to the dilaton. It is shown that
in analogy to the previously considered cases with a single nonlinear scalar
field, in DS theories there are also time periodic quasibreathers (QB)
associated to small amplitude oscillons. Exploiting the QB picture the
radiation law of the small amplitude dilatonic oscillons is determined
analytically.Comment: extended discussion on stability, to appear in JHEP, 29 pages, 7
figure
Catalyzed decay of false vacuum in four dimensions
The probability of destruction of a metastable vacuum state by the field of a
highly virtual particle with energy is calculated for a (3+1) dimensional
theory in the leading WKB approximation in the thin-wall limit. It is found
that the induced nucleation rate of bubbles, capable of expansion, is
exponentially small at any energy. The negative exponential power in the rate
reaches its maximum at the energy, corresponding to the top of the barrier in
the bubble energy, where it is a finite fraction of the same power in the
probability of the spontaneous decay of the false vacuum, i.e. at .Comment: 9 pages (standard LaTeX)+ 3 figures (one figure in LaTeX, two are
appended in PostScript). TPI-MINN-92/31-
Non-Perturbative Production of Multi-Boson States and Quantum Bubbles
The amplitude of production of on-mass-shell scalar bosons by a highly
virtual field is considered in a theory with weak
coupling and spontaneously broken symmetry. The amplitude of this
process is known to have an growth when the produced bosons are exactly at
rest. Here it is shown that for the process goes through
`quantum bubbles', i.e. quantized droplets of a different vacuum phase, which
are non-perturbative resonant states of the field . The bubbles provide a
form factor for the production amplitude, which rapidly decreases above the
threshold. As a result the probability of the process may be heavily suppressed
and may decrease with energy as , where the power
depends on the number of space dimensions. Also discussed are the quantized
states of bubbles and the amplitudes of their formation and decay.Comment: 20 pages in LaTeX + 3 figures (fugures not included, hardcopy
available on request), TPI-MINN-93/20-