セミナー 2018年

Kodai Sakurai, University of Toyama / Osaka University

Precise calculations of Higgs decay rates in various extended Higgs sectors

Seminar room, Kenkyu honkan 3F
Precision measurements of observables for the discovered Higgs boson, such as decay rates and production cross sections, play a crucial role in examining structure of the Higgs sectors. By making use of precise data of Higgs observables in future collider experiments, we aim to comprehensively test various extended Higgs models. To achieve such our goal, we previously calculated full set of renormalized Higgs boson couplings at the 1-loop level in various extended Higgs models such as the Higgs singlet model, 4 types of two Higgs doublet models and the inert doublet model. Applying those calculations, we recently computed decay rates of the Higgs boson with NLO EW and NLO QCD corrections in above models. In this talk, we discuss whether or not these models can be discriminated with deviations from the SM for the Higgs decay rates and how we extract information of mass scale of second Higgs bosons. This talk is based on arXiv:1803.01456.

Takahiro Terada, KEK

Semi-Analytic Calculation of Gravitational Wave Spectrum Induced from Primordial Curvature Perturbations

Meeting room 1, Kenkyu honkan 1F
Whether or not the primordial gravitational wave (GW) produced during inflation is sufficiently strong to be observable, GWs are necessarily produced from the primordial curvature perturbations in the second order of perturbation. The induced GWs can be enhanced by curvature perturbations enhanced at small scales or by the presence of matter-dominated stages of the cosmological history, both of which are motivated in primordial black hole scenarios to explain dark matter or the LIGO/Virgo event rate. We analytically calculate the integral in the expression of the power spectrum of the induced GWs which is a universal part independent of the primordial spectrum. This makes the subsequent numerical integrals significantly easy. In simple cases, we derive fully analytic formulae for the induced GW spectrum.
K. Kohri and T. Terada, 1804.08577 [gr-qc] (and 1802.06785 [astro-ph.CO])

Susan Gardner, Dept. of Physics & Astronomy, University of Kentucky

Permanent EDM searches and the theoretical landscape of CP violation

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
I will discuss the theoretical motivations for permanent EDM searches, as well as the theoretical interpretation of existing experimental limits in neutrons, atoms, and molecules, and I will examine how such limits combine to refine the possible TeV-scale landscape of CP violation from physics beyond the Standard Model.

甘利俊一, 理化学研究所

[第六回KEK連携コロキウム]人工知能の歴史、現状、将来: 付録ー統計神経力学の構想 

つくばキャンパス研究本館小林ホール/東海キャンパス東海1号館116号室 (TV会議中継)

Takafumi Kokubu, KEK

Inhomogeneity Effect of Density Perturbations on Condition of Primordial Black Hole Formation

Meeting room 1, Kenkyu honkan 1F
Condition for Primordial Black Hole (PBH) formation in matter dominated era including inhomogeneity effect is derived with treating general relativity. We investigate how the inhomogeneity of density perturbation affects the formation of PBHs. Black hole formation is determined by comparing two characteristic times, the formation time of the horizon and of the singularity. We investigate the threshold of the PBH formation by taking account of the speed of light propagating between the central singularity and the surface of a perturbation to be trapped.
We report our analysis implies density perturbations with larger inhomogeneity would easily lead PBHs.
[1] M. Y. Khlopov and A. G. Polnarev, Phys. Lett. 97B, 383 (1980).
[2] A. G. Polnarev and M. Y. Khlopov, Sov. Astronomy, 25, 406 (1981).
[3] T. Harada, C. M. Yoo, K. Kohri, K. i. Nakao and S. Jhingan,
Astrophys. J. 833, no. 1, 61 (2016).

Hiromasa Takaura, Kyushu University

Determination of αs from static QCD potential with renormalon subtraction

Meeting room 1, Kenkyu honkan 1F
The strong coupling constant α_s is a fundamental parameter in the standard model and requires to be determined with higher accuracy. We determine α_s from static QCD potential with a new method where a renormalon uncertainty, which is an inevitable error in perturbative predictions, is subtracted from a theoretical prediction. We obtain α_s(M_Z^2)=0.1178+0.0016/-0.0015, which is consistent with the PDG result.

Misao Sasaki, Kavli IPMU, The University of Tokyo

Scalaron as a Heavy Field and Formation of Primordial Black Holes

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
We propose a model of two-stage inflation in which a scalar field, χχ, is non-minimally coupled to Starobinsky’s R2R2 gravity. The scalaron, ϕϕ, in Starobinsky’ model drives the first stage of inflation, and χχ drives the second. At the end of the first stage, the scalaron becomes heavy and undergoes damped oscillations. This causes enhancement and oscillatory features in the curvature perturbation power spectrum. The peak in these features may give rise to copious production of primordial black holes (PBHs). For a suitably chosen set of model parameters, these PBHs may even dominate the CDM of the Universe.

Chen Zhang, National Center for Theoretical Sciences, Physics Division

Simplest Little Higgs Revisited: Hidden Mass Relation, Unitarity and Naturalness

Meeting room 1, Kenkyu honkan 1F
In this talk, I will present an analysis of the scalar potential of the Simplest Little Higgs (SLH) model in an approach consistent with the spirit of continuum effective field theory (CEFT). A hidden mass relation is obtained relating the pseudo-axion mass and top partner mass, serving as a crucial test of the SLH mechanism. I also propose a strategy of analyzing the fine-tuning problem consistent with the spirit of CEFT and apply it to the SLH. The scalar potential and fine-tuning analysis strategies investigated here should also be applicable to a wide class of Little Higgs and Twin Higgs models, which may reveal interesting relations as crucial tests of the related electroweak symmetry breaking mechanism and provide a new perspective on assessing their degree of fine-tuning.

Piljin Yi, Korea Institute for Advanced Study

Witten, Cardy, and the Holonomy Saddle

Meeting room 1, Kenkyu honkan 1F
This talk will explore topological invariants of susy gauge theories, with some emphasis on index-like quantities and the notion of holonomy saddles. We start with 1d refined Witten index computations where the twisted partition functions typically show rational, rather than integral, behavior. We will explain how this oddity is a blessing in disguise and propose a universal tool for extracting the truely enumerative Witten indices. In part, this finally put to the rest a two-decade-old bound state problems which had originated from the M-theory hypothesis. Along the way, we resolve an old and critical conflict between Kac+Smilga and Staudacher/Pestun, circa 1999~2002, whereby the notion of H-saddles emerges and plays a crucial role. More importantly, H-saddles prove to be universal features of supersymmetric gauge theories when the spacetime include a small circle: H-saddles are explored further for d=4, N=1 theories, with much ramifications on some recent claims on Cardy exponents of their partition functions.

Fred Olness, Southern Methodist U

PDF flavour determination and nCTEQ PDFs:(challenges and opportunities of QCD)

Meeting room 1, Kenkyu honkan 1F
We use nCTEQ15 nPDFs with uncertainties to identify measurements whichhave a potential impact on nuclear corrections and flavor differentiation. In particular, recent LHC W/Z vector boson production data in proton-lead and lead-lead collisions are quite sensitive to heavier flavors (especially the strange PDF). This complements the information from neutrino-DIS data. As the proton flavor determination is dependent on nuclear corrections (from heavy target DIS, forexample), this information can also help improve proton PDFs.

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