朴 云 松 朴 云 松 中国科学院研究生院 中国科学院研究生院 How to Build an Alternative to Inflation

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 Problems of Big Bang cosmology Why inflation is successful ? Why inflation is successful ? How to build an alternative How to build an alternative Summary Summary

i.

ii.

iii.

a period of accelerated expansion of early universe inflation

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 there can be a solution to the problem of standard cosmology

expansion contraction

what is the efolding number ? for perturbation, not for scale factor

inflation slow contractionslow expansion inflation

slow contraction slow expansion

expansion contraction what can lead the scale invariant scalar spectrum ?

and are same only in

is the increasing mode when The reason is

for

Piao (03) island universe (05,07) cyclic universe constant mode increasing mode

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,

island universe cyclic universe (Steinhardt et.al.)

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 ？ expansion contraction There are only a little points responsible for scale invariance. However, the perturbation is induced by background field. This is natural.

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. PBB expansion contraction some “unnatural” mechanisms

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

expansion contraction ？ background field non background field

ii. change speed of sound it might be scale Invariant for any and any evolutions expansion contraction ? however, some problems of standard cosmology will remain. some “unnatural” mechanisms

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