Summary :
The ILC Physics Case can be summarized in two main domains: precision measurements and discovery potential. Whereas the principal aim of the precision measurements concerns the Higgs, a secondary but very important aim is to study the top: to determine accurately its mass and to measure its couplings to the SM vector bosons. The top mass will be obtained at 350 GeV, by scanning the threshold of the top pair production. The top couplings to the photon and the Z0 will be measured at about 500 GeV.
For both measurements, a precise mastering of the ElectroWeak loop corrections is essential since it appears that they induce sizeable corrections to the leading mechanisms (typically 5-10%) far larger than the precision achievable at the ILC.
The goals of the TYL project “top-ILC” are twofold: strengthen further the 500 GeV analysis that has been developed in the past years using semi-leptonic events [1], and design means to control theoretically and experimentally the ElectroWeak loop corrections.
In that respect, following the first top-ILC workshop held in KeK (2013) one of the approach that is pursued is to assess the potential of the double leptonic events, where both W’s decay leptonically.
Using Monte Carlo events provided by GRACE [2], it has been shown that experimentally one can cope with the two missing neutrinos and that a Matrix Element [3] analysis of the events using Leading Order expressions [4] should provide top-coupling measurements with an accuracy similar to the one attained using the semi-leptonic events, but with different systematical effects.

French members :
F. Le Diberder, S. Bilokin, P. Colas, E. Kou, R. Poeschl, F. Richard, V. Shavy, M. Titov, B. Tuchming

Japanese members :
K. Fujii, A. Ishikawa, D. Jeans, Y. Kiyo, M. Kurata, Y. Kurihara, T. Suehara, Y. Sato, Y. Sumino, T. Tanabe, H Yamamoto

References :
[1] M.S. Amjad et al. : arXiv:1307.8102 (2013)
[2] Progress of Theoretical Physics, Vol. XX, No. X, October 1999
[3] H.J. Behrends et al., CELLO Collab. Z. Phys. C43 (1989)
[4] G. Kane, G. Ladinsky and C.P. Yuan, Phys. Rev. D 45 (1992)

Summary :

Several astrophysical or cosmological observations (evidences for dark matter, baryon asymmetry, inflation...) require an extension of the Standard Model of particle physics (so-called “beyond the standard model” (BSM) physics). The links between cosmology and particle physics heavily rely on the understanding on the history of the universe, which is often based on standard assumptions. For instance: an inflationary epoch produces a quasi-power law spectrum of perturbations (seeds of current structures) and ends in a radiation dominated period, during which conventional electroweak symmetry and QCD breaking happen as crossovers, according to the SM. Dark Matter is usually considered to be a particle relic, once in thermal contact with other SM species, etc. We are exploring possible departures from this simple picture. In the classically conformal extension of the SM, S. Iso, P. Serpico, and K. Shimada found that the chiral condensation in QCD can play an important role in the dynamics of the electroweak symmetry breaking. The phase transition becomes of the first order type and accordingly generates large gravitational waves that can be detected by future gravitational wave detectors [2]. Always related to gravitational waves, it is well known that the LIGO interferometers have detected their first sources of gravitational waves, from coalescences of binary black holes (BHs). While such binaries have long been considered an attractive candidate, the mechanism to produce them is not established, yet, in particular for such high masses (about 30 times the mass of the sun). It has also been conjectured that such BH may be of primordial origin. Their formation requires a significant departure from the simplest inflationary models, and at the same time it would lead to non-standard cosmological signatures, which can be searched for. This is another sector we are working on (notably k. Kohri with P. Serpico and V. Poulin) and some results are expected in the current year

French members :
P. Serpico, G. Bélanger, F. Boudjema, K. Shimada

Japanese members :
K. Kohri, S. Iso

References :
[1] S. Iso, K. Kohri and K. Shimada, "Dynamical fine-tuning of initial conditions for small field inflation," Phys. Rev. D 93, 084009 (2016) [arXiv:1511.05923]
[2] S. Iso, P. D. Serpico and K. Shimada, "QCD-Electroweak first order phase transition in supercooled universe,'' arXiv:1704.04955

Summary :
New particles and interactions beyond the Standard Model (SM) of particle physics are required to explain neutrino masses and mixing angles. The search for traces of this new physics (NP) is pursued on many fronts. One possibility is to look directly for the new particles implicated in neutrino mass generation, for instance at the LHC. A complementary approach seeks indirectly new interactions among rare processes, such as charged lepton flavour violation (CLFV). CLFV transitions can be induced by the observed massive neutrinos in the SM, at unobservable rates suppressed by 10 e-48. A detectable rate would point to the existence of new heavy particles, as may arise in models that generate neutrino masses, or that address other puzzles of the SM such as the hierarchy problem. Observations of CLFV are therefore crucial to identifying the NP of the lepton sector, providing information complementary to direct searches. The experimental sensitivity to a wide variety of CLFV processes is systematically improving. Current bounds on branching ratios of the muon to electron flavour changing processes are currently of order of 10 e-13. Future experimental sensitivities should improve by several orders of magnitude, in particular, the COMET and Mu2e experiments which aim to reach a sensitivity to μ-e conversion on nuclei of ∼ 10 e-16. Given such rapid experimental progress in the future, our main area of research is to study in details physics opportunities for the CLFV processes, and explore new opportunities, by the joint collaboration of theorists and experimentalists between Japan and France. We have already made the first research achievement, on the study of spin-depended muon to electron conversion, which has been published in a scientific journal of Physics Letters in 2017 [1]. This physics case has never previously been considered. We will explore further unique physics cases in our research collaboration. To achieve this goal, we are planning to organize informal meetings and workshops between French and Japanese.

French members :
S. Davidson, A. Saporta, A. M.Teixeira

Japanese members :
Y. Kuno, J. Sato, K. Tobe, M. Yamanaka, S. Kanemura

References :
[1] V. Cirigliano, S. Davidson and Y. Kuno, “Spin-dependent μ→e conversion“, Phys. Lett. B771 (2017) 242-246
[2] S. Davidson, Y. Kuno, A. Saporta, “Spin-dependent μ→e conversion on light nuclei”, Eur.Phys.J. C78 (2018) 109

Summary :
A compact and highly granular electromagnetic calorimeter at ILC is one of the key requirements for PFA high precision jet reconstruction and realization of ILC physics potential. R&D of silicon-tungsten calorimeter is the goal of this project. We plan to finalize the optimization of the ECAL geometry (dimensions and number of layers), to build and to test a detector (so-called "active sensor unit", or ASU) with 1024 channels per PCB serving 4 silicon sensors with 16x16 pixels, improve the DAQ software and to work on integration of several ASUs into one ILC full-scale detector. In parallel, we plan to test various designs of silicon sensors and their radiation hardness.

French members :
V. Boudry, V. Balagura, J-C. Brient, R. Cornat, A. Irles R. Poeschl, K. Shpak, D. Zerwas

Japanese members :
D. Jeans, Y. Kamiya, K.Kawagoe, S. Komamiya, H. Nakanishi, T. Suehara, H. Yamashiro

References :
[1] T.H.Tran, "ILD SiW ECAL and sDHCAL dimension-performance optimisation", report at LCWS'13, arXiv:1404.3173 [physics.ins-det]
[2] Ch.Kozakai et al., "Robustness of a SiECAL used in Particle Flow Reconstruction", report at LCWS'13, arXiv:1404.0124 [physics.ins-det]
[3] T.Tomita et al., "A study of silicon sensor for ILD ECAL", report at LCWS'13, arXiv:1403.7953 [physics.ins-det]
[4] Editors: T.Behnke et al., "The International Linear Collider Technical Design Report - Volume 4: Detectors", arXiv:1306.6329 [physics.ins-det]

website :
https://twiki.cern.ch/twiki/bin/view/CALICE/SiWEcal