How to Build
an Alternative to Inflation
朴 云 松
中国科学院研究
生院
The idea behind inflation should be more
interesting than inflation self, which
may bring us more thoughts
are there alternatives to inflation ?

Problems of Big Bang cosmology

Why inflation is successful ?

How to build an alternative

Summary
i.
ii.
iii.
inflation
a period
of accelerated expansion
of early universe
if it is actually inflation,
the amusements left are
play models
and
fit observations
the game is actually ...
however,
it may be not inflation ?
There can be a scenario ?
it can
solve same problems (or some of problems)
with those solved by inflation
generate scale invariant primordial
perturbation
it requires a|H| increases with time
Thus if
.
a 0
..
a 0
.
a 0
..
a 0
there can be a solution to
the problem of standard cosmology
contraction
expansion
what is the efolding number ?
for perturbation,
not for scale factor
inflation
inflation
slow expansion
slow contraction
slow contraction
slow expansion
contraction
expansion
what
can lead
the scale invariant scalar spectrum ?
and
are same only in
The reason is
is the increasing mode
when
for
constant mode
increasing mode
cyclic universe
Piao (03)
island universe (05,07)
island
universe
The cyclic and island
a is nearly unchanged.
H is rapidly increased.
The inflation
a is rapidly increased.
H is nearly unchanged.
This duality is a natural result of duality
between their background evolutions.
how to distinguish inflation (
and scenarios with
)
i.non-Gaussianity
In general, non-Gaussianity
for inflation, it is small,
however, it can be large by other methods.
for
, it is natural large
for example, if
,
cyclic universe
(Steinhardt et.al.)
island universe
ii. Tensor spectrum
Steinhardt et.al.
For
there are lots of studies.
However, the problems
It is not an attractor solution.
It leads to
Thus
contraction
expansion
？
There are only a little points
responsible for scale invariance.
However, the perturbation is induced by
background field.
This is natural.
some “unnatural” mechanisms
i. non background field
recall “curvaton” in inflation game
Thus the perturbation can be induced by
also light field.
it initially is used in PBB
picture.
contraction
expansion
PBB
In principle, the scale invariance can be
obtained for any
.
however, it requires
a special behavior of field.
In general, a. non minimal coupled kinetic term
b. change of mass with time
contraction
expansion
？
background field
non background field
some “unnatural” mechanisms
ii. change speed
of sound
it might be scale
Invariant for any
and any evolutions
however,
some problems of
standard cosmology
will remain.
expansion
contraction ?
Summary
the idea behind inflation is more
interesting than inflation self.
inflation is consistent,
however, there are alternatives.
may be tested by
coming observations.
Have all possibilities been explored ?
……
Thank You