2017 Fiscal Year Research-status Report
| Project/Area Number |
16K05336
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| Research Institution | High Energy Accelerator Research Organization |
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Principal Investigator |
北澤 良久 大学共同利用機関法人高エネルギー加速器研究機構, 素粒子原子核研究所, 教授 (10195258)
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| Project Period (FY) |
2016-04-01 – 2021-03-31
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| Keywords | correlation functions / single field inflation / non-Gaussianity / IR logarithmic effects / shift symmetry breaking / a linear potential |
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| Outline of Annual Research Achievements |
We investigate inflationary correlation functions in single field inflation models. We adopt a BRST formalism where locality and covariance at sub-horizon scale are manifest. The scalar and tensor perturbations are identified with those in the comoving gauge which become constant outside the cosmological horizon. Our construction reproduces the identical non-Gaussianity with the standard comoving gauge. The accumulation of almost scale invariant fluctuations could give rise to IR logarithmic corrections at the loop level. We investigate the influence of this effect on the subhorizon dynamics. Since such an effect must respect covariance, our BRST gauge has an advantage over the standard comoving gauge. We estimate IR logarithmic effects to the slow-roll parameters at the one-loop level. We show \epsilon receives IR logarithmic corrections while it is not the case for η. We point out that IR logarithmic effects provide the shift symmetry breaking mechanism. This scenario may lead to an inflation model with a linear potential.
One of the major puzzles of inflation theory is to explain why slow-roll parameters are small.
Shift symmetry with respect to the inflaton field \phi→ \phi + c may be necessary to explain
it. It is often broken by hand to construct inflation models leading to proliferation of them.
We need a better understanding of this symmetry breaking mechanism. The IR effect to
\epsilon could solve this difficulty.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
We investigated cosmological correlation functions in a BRST gauge where locality and covariance at the sub-horizon scale are manifest. Since the cosmological perturbations are frozen at the super-horizon scale, it is determined by the dynamics of the sub-horizon scale. The slow-roll inflation is characterized by \epsilon and η parameters which represent the slope and curvature of the inflaton potential. Since they evolve with time even at the classical level, they could obtain IR logarithmic corrections. In fact we argue that \epsilon receives IR logarithmic effects and undergoes additional quantum evolution. On the other hand, η does not receive IR logarithmic correction. The covariance of the theory at the sub-horizon scale has played an important roll in determining IR logarithmic corrections to the slow-roll parameters. In this respect, the BRST gauge has the advantage of keeping manifest locality and covariance at the sub-horizon scale.
In this investigation, we introduce the propagators in BRST formalism. The advantage of this gauge over the standard comoving gauge is its locality. The covariance at sub-horizon scale is more manifest in this gauge. These features allow us to identify IR logarithmic effects at sub horizon scale. We explain how to reproduce the identical cosmological correlators with the comoving gauge which become constant outside the horizon. We investigate infrared logarithmic effects to scalar perturbation. We show \epsilon receives nontrivial correction to the leading order of slow-roll parameters while it is not the case for η.
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| Strategy for Future Research Activity |
One of the major puzzles of inflation theory is to explain why slow-roll parameters are small.
Shift symmetry with respect to the inflaton field \phi → \phi+ c may be necessary to explain it. It is often broken by hand to construct inflation models leading to proliferation of them. We need a better understanding of this symmetry breaking mechanism. The IR effect to \epsilon could solve this difficulty as this quantum effect may provide a shift symmetry breaking mechanism. This scenario may lead to an inflation model with a linear potential.
Inflation model with the linear potential is currently under scrutiny. We must observe tensor mode soon if IR logarithmic corrections are responsible for shift symmetry breaking.Thus this scenario is very interesting and currently relevant against observational test. Theoretically we need to clarify why \eta parameter is not renormalized by IR logarithmic effects while \epsilon is renormalized. We believe that \eta is nothing but the mass of an inflaton and it is not renormalized due to the energy-momentum conservation.
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| Causes of Carryover |
(理由）昨年１１月にKEKにおいて、2nd East Asian Joint Workshop on Fields and Stringsが開催された。本会議においては、ダークエネルギーの時間依存性と微視的理論の研究に密接に関連した場の理論及び弦理論に関して、中国、韓国、台湾及び日本の研究者の研究成果発表及び参加者間の議論が行われた。本国際会議開催費用としてこれらの参加者への滞在費援助が必要であり、その開催費用の一部に充当す予定であった。総研大からもサポートが得られたので、インドからの研究者の招聘にも使用する事ができた。
(使用計画) 今年度６月に沖縄科学技術大学院大学で国際会議Strings2018の開催を予定している。本会議においては、ダークエネルギーの時間依存性と微視的理論の研究に密接に関連した弦理論に関して、国際的に著名な研究者の研究成果発表及び参加者間の議論が行われる。本国際会議開催費用としてこれらの参加者への滞在費援助が必要であり、その開催費用の一部に充当する。
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Research Products
(4 results)
