Proceedings of International Conference on Physics in ... - KEK

small for the electric field weaker than Schwinger limit <strong>of</strong>
Eq. (3).
It is very important to know that for the plane wave
<strong>of</strong> laser field in the vacuum, the two scalars S and P
disappear and no tunneling effect can be expected even
with the laser intensity higher than the Schwinger limit <strong>of</strong>
Eq. (4). So, we are required to deform the laser field from
the plane wave relation to maximize the Lorentz
invariants S and P, especially the scalar P in Eqs. (8) and
(9). In order to optimize with realistic optics, not only the
colliding laser scheme but also strongly tightly focused
laser field is proposed [32]. In addition, multiple colliding
laser pulses method is also proposed and evaluated
quantitatively how less laser energy is enough to produce
one pair [33]. We have proposed another tightly focused
laser with use <strong>of</strong> a radially polarized laser [34].
In the above three schemes, it is concluded that the
tunneling effect starts with the laser intensity more than
10 26 -10 27 W/cm 2 . Although the tunneling effect is not
substantial like Schwinger limit, the seed pairs are pro-
duced in the pure vacuum and the prolific pair production
and the resultant vacuum breakdown might be expected
by the avalanche mechanism. Of course, very precise cal-
culation is necessary with the computational modeling
briefly mentioned previously. In this case, solving the
Maxwell equations self-consistently is very important to
see if the laser field is scattered out without being focused
like the case <strong>of</strong> pure vacuum. This is because the
appearance <strong>of</strong> the pairs means average refractive index
changes as a function <strong>of</strong> time at the focused point.
When the laser intensity reaches the Schwinger limit
Eq. (4), the pair creation by the tunneling effect becomes
dominant and spontaneous creation <strong>of</strong> the pairs occur at
all the place where the value <strong>of</strong> Eq. (7) is large enough.
In this case, the interesting point <strong>of</strong> research is how the
avalanche effect is still important for the pair creation
process. In addition, we also expect the creation <strong>of</strong> low
energy hadron and hadron pairs such as π and π ± .
What kind <strong>of</strong> lepton pairs and hadron mixture or quark-
gluon mixture plasma is produced is a very interesting
subject.
LABORATORY COSMOLOGY AND
MODELING QUARK-GLUON PLASMA
We can expect to do a variety <strong>of</strong> model experiments
for open questions in high-energy astrophysics. The
investigation <strong>of</strong> the plasma properties <strong>of</strong> highly rela-
tivistic electron positron plasmas and jets is essential for
example, AGN jets and the jets related to the gamma-ray
bursts [35]. In the case <strong>of</strong> “quiet” pair production in gold
foil as described relating to Fig. 2, the am-bipolar field
accelerates the positron to produce relativistic pair plasma
in the jet-like structure. This is good to model the
propagation <strong>of</strong> pair plasma jets in the Universe.
In the case <strong>of</strong> “violent” pair creation via the vacuum
breakdown, it is not clear what kind <strong>of</strong> energy distribution
and angular distribution <strong>of</strong> the pair plasma is produced
and how we can control them. In addition the distribution
<strong>of</strong> gamma-ray is also open question. It may not be in the
thermodynamic equilibrium state, while the physical
dynamics in the highly relativistic “pair fireball” is very
interesting matter to study liner and nonlinear collective
phenomena as plasma physics. Whether a collisionless
shock formation may observed after the nonlinear stage is
very hot topics in the GRB physics [36]. For example, this
plasma would be a good test bed to verify and validate the
computational modeling. It is very challenging, while the
improvement <strong>of</strong> such simulation code compared to the
real experiment is very much beneficial also to the
modeling <strong>of</strong> Quark-Gluon plasma (QGP), where the color
force is dominant than the electric force. It is said that
non-Abelian system like QGP would become thermo-
dynamic equilibrium in an extremely short time [37]. In
addition, we may be able to identify if the avalanche
effect plays an important role in the formation <strong>of</strong> QGP in
extremely tiny space and time.
As schematically shown in Fig. 6, the QGP created
through vacuum breakdown by color field is <strong>of</strong> the order
<strong>of</strong> 10 -12 cm (=10fm) and the life time <strong>of</strong> QGP is about
10fm/c = 3×10 -21 s. In the RHIC [38] and LHC [39]
experiment for QGP, therefore, it is difficult to measure
the plasma state and, for example, the equation <strong>of</strong> state <strong>of</strong>
Fig. 6 Laser produced electron pair fireball will be a
model experiment <strong>of</strong> quark-gluon plasma (QGP)
dynamics.