Narrow Results

The ATLAS and CMS groups have recently reported an excess at around 750 GeV with the local significance by about 3$\sigma$ in the diphoton channel at the 13 TeV LHC. We give a possible explanation for the excess by a composite pseudo scalar $(P^0)$ predicted in the one-family model of walking technicolor.

In contrast to the folklore that Technicolor (TC) is a "Higgsless theory", we shall discuss existence of a composite Higgs boson, Techni-Dilaton (TD), a pseudo-Nambu-Goldstone boson of the scale invariance in the Scale-invariant/Walking/Conformal TC (SWC TC) which generates a large anomalous dimension γ_m ≃ 1 in a wide region from the dynamical mass of the techni-fermion all the way up to the intrinsic scale Λ_TC of the SWC TC (analogue of Λ_QCD), where Λ_TC is taken typically as the scale of the Extended TC scale Λ_ETC: Λ_TC ≃ Λ_ETC ~ 10³TeV (≫ m). All the techni-hadrons have mass on the same order , which in SWC TC is extremely smaller than the intrinsic scale Λ_TC ≃ Λ_ETC, in sharp contrast to QCD where both are of the same order. The mass of TD arises from the non-perturbative scale anomaly associated with the techni-fermion mass generation and is typically 500-600 GeV, even smaller than other techni-hadrons of the same order of , in another contrast to QCD which is believed to have no scalar bound state lighter than other hadrons. We discuss the TD mass in various methods, Gauged NJL model via ladder Schwinger-Dyson (SD) equation, straightforward calculations in the ladder SD/ Bethe-Salpeter equation, and the holographic approach including techni-gluon condensate. The TD may be discovered in LHC.

We study a two-component dark matter candidate inspired by the minimal walking technicolor (WTC) model. Dark matter consists of a dominant strongly interactive massive particle (SIMP)-like dark atom component made of bound states between primordial helium nuclei and a doubly charged technilepton and a small WIMP-like component made of another dark atom bound state between a doubly charged technibaryon and a technilepton. This scenario is consistent with direct search experimental findings because the dominant SIMP component interacts too strongly to reach the depths of current detectors with sufficient energy to recoil and the WIMP-like component is too small to cause significant amount of events. In this context, a metastable technibaryon that decays to $e^{+}{e}^{+}$, ${\mu }^{+}{\mu }^{+}$ and ${\tau }^{+}{\tau }^{+}$ can, in principle, explain the observed positron excess by AMS-02 and PAMELA, while being consistent with the photon flux observed by FERMI/LAT. We scan the parameters of the model and we find the best possible fit to the latest experimental data. We find that there is a small range of parameter space that this scenario can be realized under certain conditions regarding the cosmic ray propagation and the final state radiation (FSR). This range of parameters fall inside the region where the current run of large hadron collider (LHC) can probe, and therefore it will soon be possible to either verify or exclude conclusively this model of dark matter.

Stable multiple charged particles can possess electroweak charges, as per the walking technicolor models. An asymmetry of these particles is balanced by sphaleron transitions which among other things can provide an excess of baryons and/or leptons. A possibility to generate sufficient amount of particles with the charge $-2n$ to explain the observed dark matter density by dark atoms (which are bound states of multiple charged techniparticles with n helium nuclei) is considered in the framework of thermodynamic approach.

LatKMI Collaboration has been studying SU(3) gauge theories with large numbers of fermion flavors, N_f. Here, we report results of lattice simulations for SU(3) gauge theory with four fundamental fermions. We first show fermion mass dependence of F_π,$〈\overline{q}q〉$M_π, M_ρ and chiral extrapolations of them, showing the evidence of chiral symmetry breaking. Then, we show preliminary result of the measurement of the mass of the flavor-singlet scalar bound state.

In contrast to the folklore that Technicolor (TC) is a "Higgsless theory", we shall discuss existence of a composite Higgs boson, Techni-Dilaton (TD), a pseudo-Nambu-Goldstone boson of the scale invariance in the Scale-invariant/Walking/Conformal TC (SWC TC) which generates a large anomalous dimension γ_m ≃ 1 in a wide region from the dynamical mass of the techni-fermion all the way up to the intrinsic scale Λ_TC of the SWC TC (analogue of Λ_QCD), where Λ_TC is taken typically as the scale of the Extended TC scale Λ_ETC: Λ_TC ≃ Λ_ETC ~ 10³TeV (≫ m). All the techni-hadrons have mass on the same order , which in SWC TC is extremely smaller than the intrinsic scale Λ_TC ≃ Λ_ETC, in sharp contrast to QCD where both are of the same order. The mass of TD arises from the non-perturbative scale anomaly associated with the techni-fermion mass generation and is typically 500-600 GeV, even smaller than other techni-hadrons of the same order of , in another contrast to QCD which is believed to have no scalar bound state lighter than other hadrons. We discuss the TD mass in various methods, Gauged NJL model via ladder Schwinger-Dyson (SD) equation, straightforward calculations in the ladder SD/ Bethe-Salpeter equation, and the holographic approach including techni-gluon condensate. The TD may be discovered in LHC.

QCD with 2 flavours of massless colour-sextet quarks is studied as a theory which might exhibit a range of scales over which the running coupling constant evolves very slowly (walks). We simulate lattice QCD with 2 flavours of sextet staggered quarks to determine whether walks, or if it has an infrared fixed point, making it a conformal field theory. Our initial simulations are performed at finite temperatures T = 1/N_ta (N_t = 4 and N_t = 6), which allows us to identify the scales of confinement and chiral-symmetry breaking from the deconfinement and chiral-symmetry restoring transitions. Unlike QCD with fundamental quarks, these two transitions appear to be well-separated. The change in coupling constants at these transitions between the two different temporal extents N_t, is consistent with these being finite temperature transitions for an asymptotically free theory, which favours walking behaviour. In the deconfined phase, the Wilson Line shows a 3-state signal. Between the confinement and chiral transitions, there is an additional transition where the states with Wilson Lines oriented in the directions of the complex cube roots of unity disorder into a state with a negative Wilson Line.

Investigation of the SU(3) gauge theory with many fermions for the quest for the walking technicolor theory as a KMI project is described. The theory, if it is successfully constructed, can supersede the standard model Higgs sector, and thus can be a candidate of the theory of new physics. We utilize the KMI high-performance computing system φ, perform the numerical simulation adopting a state-of-the-art lattice fermion formulation. A hint of the number of fermions for the candidate of the walking technicolor theory is emerging.

We investigate walking signals of N_f = 8 QCD through meson spectrum using the highly improved staggered quark (HISQ) action. Our data (the pion decay constant, the pion and ρ meson masses and the chiral condensate) for the N_f = 8 QCD are consistent with the spontaneously broken chiral symmetry in the chiral limit extrapolation of the chiral perturbation theory (ChPT). Remarkably enough, while the N_f = 8 data near the chiral limit are well described by the ChPT, those for the relatively large fermion bare mass m_f away from the chiral limit actually exhibit a finite-size hyperscaling relation, suggesting a large anomalous dimension γ_m ∼ 1. This implies that there exists a remnant of the infrared conformality, and suggests that a typical technicolor (“one-family model”) as modeled by the N_f = 8 QCD can be a walking technicolor theory.

The LatKMI collaboration is studying systematically the dynamical properties of N_f = 4, 8, 12, 16 SU(3) gauge theories using lattice simulations with (HISQ) staggered fermions. Exploring the spectrum of many-flavour QCD, and its scaling near the chiral limit, is mandatory in order to establish if one of these models realises the Walking Technicolor scenario. Although lattice technologies to study the mesonic spectrum are well developed, scalar flavour-singlet states still require extra effort to be determined. In addition, gluonic observables usually require large-statistic simulations and powerful noise-reduction techniques. In the following, we present useful spectroscopic methods to investigate scalar glueballs and scalar flavour-singlet mesons, together with the current status of the scalar spectrum in N_f = 12 QCD from the LatKMI collaboration.

In this talk I argue that a light techni-dilaton exists in models of walking technicolor near the conformal window. The light techni-dilaton then mixes with the composite Higgs, which is predicted to be narrow and light in walking technicolor models. It is an interesting possibility that the newly discovered boson at LHC might be a mixed state of techni-dilaton and the composite Higgs.