Taro Kimura, Keio University
Boundary condition analysis of topological insulators
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Study of topological insulators and superconductors (topological phases of matter) is currently an active research area in condensed-matter physics. One of the most important aspects of them is the renowned relation between bulk and edge states, called the bulk/edge correspondence. The edge state, localized at the material boundary, is sensitive to a boundary condition definitely, but how the boundary condition affects the edge state has not been studied in a systematic way so far. We tackle this problem with a minimal model of topological insulator, and show boundary condition dependence of the edge state, in particular, its energy spectrum and wavefunction behavior. We also argue how such a generic boundary condition is realized in lattice models. This talk is based on a collaboration with K. Hashimoto and X. Wu (Osaka): [arXiv:1509.04676], [arXiv:1602.05577] and work in progress.
Masazumi Honda, Weizmann Institute
How to resume perturbative series in supersymmetric gauge theories
Meeting room 1, kenkyu honkan 1F, slides (kek.jp only) Perturbative series in quanum field theory is typically divergent.
Perturbative series in quanum field theory is typically divergent.
There is a standard method to resum divergent series called Borel resummation.
While perturbative series in typical field theory is expected to be non-Borel summable,
it is important to ask when perturbative series is Borel summable and if it is non-Borel summable,
what is a correct way to resum the perturbative series.
In my talk I first discuss that we can prove Borel summability of perturbative series
in 4d N=2 and 5d N=1 supersymmetric gauge theories with Lagrangians for various observables.
It turns out that exact results in these theories can be obtained by summing over the Borel resummations with every instanton number.
I also discuss perturbative series in general 3d N=2 supersymmetric Chern-Simons matter theory,
which is given by a power series expansion of inverse Chern-Simons levels.
We prove that the perturbative series are always Borel summable along imaginary axis.
It turns out that the Borel resummations along this direction are the same as exact results.
[PRL116,no.21,211601(2016) and arXiv:1604.08653]
Tomoya Kinugawa, ICRR, The University of Tokyo
Binary black hole remnants of First stars for the gravitational wave source
Meeting room 1, Kenkyu honkan 1F
Using our population synthesis code, we found that the typical chirp mass of binary black holes (BH-BHs) whose origin is the first star (Pop III) is ~30Msun with the total mass of ~60Msun so that the inspiral chirp signal as well as quasi normal mode (QNM) of the merging black hole are interesting targets of LIGO,VIRGO and KAGRA (Kinugawa et al.2014 and 2016). The detection rate of the coalescing Pop III BH-BHs is ~ 180 events/yr (SFR_p/(10^{-2.5} Msun /yr/Mpc^3))*([f_b/(1+f_b)]/0.33)*Err_sys in our standard model where SFR_p, f_b and Err_sys are the peak value of the Pop III star formation rate, the binary fraction and the systematic error with Err_sys=1 for our standard model, respectively. Furthermore, We found that the chirp mass has a peak at ~30Msun in most of parameters and distribution functions (Kinugawa et al.2016). This result predicted the gravitational wave events like GW150914 and LIGO paper said ‘recently predicted BBH total masses agree astonishingly well with GW150914 and can have sufficiently long merger times to occur in the nearby universe (Kinugawa et al. 2014)’ (Abbot et al. ApJL 818,22 (2016)). Nakano, Tanaka & Nakamura 2015 show that if S/N of QNM is larger than 35, we can confirm or refute the General Relativity more than 5 sigma level. In our standard model, the detection rate of Pop III BH-BHs whose S/N is larger than 35 is 3.2 events/yr (SFR_p/(10^{-2.5}Msun/yr/Mpc^3))*([f_b/(1+f_b)]/0.33)* Err_sys. Thus, there is a good chance to check whether GR is correct or not in the strong gravity region and to check indirectly the existence of Pop III massive stars by gravitational wave.
Takahiro Tanaka, Kyoto University
Gravitational waves as a new probe of physics
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
There was a first direct detection of gravitational waves last year. This informed us of the dawn of the era of gravitational wave physics. The perspective of future observation became definitely brighter than before. Although the well-known guaranteed source of gravitational waves, binary neutron star merger, has not been detected, it will be soon or later detected as the world-wide network of gravitational wave detection develops. Furthermore, the possibility of early realization of future space mission might be increasing. I’d like to give some perspective on gravitational physics and discuss the challenging issues that requires theoretical study.
Yuko Urakawa, Nagoya University
Recent progress on infrared issues in inflationary universe
Meeting room 1, Kenkyu honkan 1F
It has been known that a naive computation of loop corrections in inflationary universe gives rise to a pathologically large enhancement of the infrared (IR) contributions. In this talk, I will overview the recent progress on the IR issues during inflation. In particular, for the adiabatic and tensor perturbations, we can show that the IR pathology goes away, as far as we preserve the invariance under the large gauge transformations, which diverge at the spatial infinity. I also show a couple of other consequence of the invariance under the large gauge transformation; 1) the consistency relations, which connect (n+1)-point functions with one soft leg and n-point functions 2) the conservation of the curvature perturbation at large scales in the presence of the radiative corrections of heavy fields.
Kazuya Yonekura, IPMU
Gauge interactions and topological phases of matter
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only) We initiate the study of the effects of strong gauge interactions on the properties of the topological phases of matter.
We initiate the study of the effects of strong gauge interactions on the properties of the topological phases of matter.
In particular, we discuss fermionic systems with three spatial dimensions, protected by time reversal symmetry.
We first derive a sufficient condition for the introduction of a dynamical Yang-Mills field to preserve the topological phase of matter,
and then show how the massless pions capture in the infrared the topological properties of the fermions in the ultraviolet.
Finally, we show how the S-duality of N=2 supersymmetric SU(2) gauge theory with Nf=4 flavors can be used to show the
mod 16 behavior of topological superconductors.
青木秀夫, 東大理学系・産総研
[理論センター・構造物性研究センター共催セミナー] 超伝導の最近の進展
4号館1F セミナーホール 最近でも様々に発展している超伝導をoverviewする。先ず物質としては、高温超伝導銅酸化物は、最近高圧下でゼロ抵抗として観測されたようにTcは150Kを超えるが、相図については未だに混沌としている。鉄系超伝導は様々なファミリーがあり、100K程度のTcをもつ単原子層も報告されており、多彩な相図が議論されている。軽元素系超伝導体では、硫化水素において最近超高圧下でTcが200Kを超えたが、従来型超伝導とされる。
最近でも様々に発展している超伝導をoverviewする。先ず物質としては、高温超伝導銅酸化物は、最近高圧下でゼロ抵抗として観測されたようにTcは150Kを超えるが、相図については未だに混沌としている。鉄系超伝導は様々なファミリーがあり、100K程度のTcをもつ単原子層も報告されており、多彩な相図が議論されている。軽元素系超伝導体では、硫化水素において最近超高圧下でTcが200Kを超えたが、従来型超伝導とされる。
グラフェンでも超伝導が観測されている。非平衡（レーザー照射下）では10 ps程度では室温超伝導も報告されている。
理論としては、電子間多体相互作用による非従来型超伝導という描像はおおむね確立しているが、電子相関をより正しく扱う方法論の開発もふくめて、進展が続いている。トポロジカル超伝導、ボソン交換機構を超えた機構、非平衡超伝導機構などのエキゾチックな超伝導についても触れる。
Roberto Franceschini, CERN
What is X(750)? and what to do with that?
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
In this talk I will review the experimental results about hints of significant deviation from SM predictions in the diphoton mass spectrum. I will also discuss the interpretation of this putative signal in relation to other searches for new phenomena carried out at the LHC. After this phenomenological characterization, I will motivate how new strong interactions at the TeV scale are a leading candidate to explain the putative signal and I will discuss a few examples of Goldstone bosons and related degrees of freedom that can account for the putative signal. Furthermore I will discuss key observations to be carried out in the future to test the nature of the theory behind the putative signal, *e.g.* the CP parity of the new states and their pair production.
Vladimir Gudkov, University of South Carolina
Time-Reversal Invariance Violation in Neutron Nuclei Interactions
Meeting room 1, Kenkyu honkan 1F
Time Reversal Invariance Violating (TRIV) effects in neutron transmission through a nuclei target are discussed. We explore the possibility to search TRI violation using two important advantages of neutron nuclei interactions: the possibility of the enhancement of TRIV observables by many orders of magnitude, and the relatively large number of the nuclear targets, which provides the assurance of avoiding possible “accidental” cancelations of TRIV effects due to unknown structural factors related to the strong interactions. The absence of final state interactions for the set of specific observables makes these neutron experiments complementary to electric dipole moment (EDM) measurements. The comparison of expected results in neutron scattering at new high flux Spallation Neutron Sources with the existing limits on neutron, nuclear and atomic electric dipole moments (EDMs) shows that TRIV observables in neutron scattering can essentially improve the current limits on the TRIV interactions.
Masatoshi Yamada, Kanazawa University
Non-perturbatively renormalizable quantum gravity and hierarchy problem
Meeting room 1, Kenkyu honkan 1F
