Presentation on theme: "Shinji Takeda Kanazawa U. in collaboration with Masashi Hayakawa, Shunpei Uno (Nagoya U.) Ken-Ichi Ishikawa, Yusuke Osaki (Hiroshima U.) Norikazu Yamada."— Presentation transcript:
Shinji Takeda Kanazawa U. in collaboration with Masashi Hayakawa, Shunpei Uno (Nagoya U.) Ken-Ichi Ishikawa, Yusuke Osaki (Hiroshima U.) Norikazu Yamada (KEK) Running coupling constant of ten-flavor QCD with the Schroedinger functional method arXiv: (will appear in PRD) Symposium on Lattice gauge theory at U. of Wuppertal 2/5/2011
Contents I. Introduction Physics background Walking Technicolor Conformal window II. Lattice calculation of running coupling III. Summary
Successes of Lattice QCD ‣ Hadron masses and their interactions ‣ ‣ The SM parameters ‣ Weak matrix elements ‣... Scholz lattice 2009 Lattice calculations truly reliable. Apply to Something different
LHC era Use Lattice to explore LHC physics ‣ Higgs mechanism ‣ Physics above the EW scale ‣ Among many New Physics candidates, Technicolor is attractive and best suited for Lattice Simulation
➜ New strong interaction SU(N TC ): technicolor ➜ At Λ TC ∼v weak, technifermion condensate 〈T R T L 〉 ➜ Gives dynamical SU(2) L xU(1) Y breaking ➜ New strong interaction SU(N TC ): technicolor ➜ At Λ TC ∼v weak, technifermion condensate 〈T R T L 〉 ➜ Gives dynamical SU(2) L xU(1) Y breaking Technicolor (TC) Technicolor (TC) [Weinberg(‘79), Susskind(‘79)] Alternative for Higgs sector of SM model No fine tuning ➜ 〈TT〉breaks chiral symmetry SU(2) L ×SU(2) R ➜ Produce technipion π TC (NG bosons) ➜ π TC become longitudinal components of W and Z ➜ M W = M z cosθ W = ½gF π (F π = v weak =246 GeV) ➜ 〈TT〉breaks chiral symmetry SU(2) L ×SU(2) R ➜ Produce technipion π TC (NG bosons) ➜ π TC become longitudinal components of W and Z ➜ M W = M z cosθ W = ½gF π (F π = v weak =246 GeV)
Extended TC Eichten(‘80) Susskind(‘79) How do SM fermion get mass? ⇒ Extended TC ➜ New gauge theory SU(N ETC ), N ETC >N TC T ETC =(T TC,f SM ) ➜ Assuming SSB: SU(N ETC ) ➔ SU(N TC )xSM at Λ ETC >>Λ TC ➜ New gauge theory SU(N ETC ), N ETC >N TC T ETC =(T TC,f SM ) ➜ Assuming SSB: SU(N ETC ) ➔ SU(N TC )xSM at Λ ETC >>Λ TC : fermion mass : FCNC G ff TT
Walking TC Holdom(‘81) Yamawaki et al. (‘86) Solving tension of SM fermion mass VS. FCNC μ M ETC g 2 (μ) g 2 SχSB M TC g 2 initial Classic TC or QCD-like theory Walking TC If γ=O(1): Large enhancement
Find the location of N f c in various GT. Conformal Window SχSB & Confining Conformal Asymptotic non-free NfNf ⇦ QCD N f af NfcNfc 0 Speculation on “Phase diagram” of GT ⇦ WTC?
Prediction phase (2013?-) Perform large-scale lattice simulation of candidate theories to find the precise values for f π, m ρ, (m σ ), Σ, S-parameter,... Searching phase (-2012?) Strategy on the lattice Now is in Searching phase. Prediction phase on the Next-Generation supercomputer? Calculate hadron spectrum to see scaling behavior Calculate running coupling and anomalous dimension directly on the lattice.
So far, the following SU(Nc) gauge theories have been intensively studied Candidates for WTC NcNcNcNc NfNfNfNfRep. Running g 2 spectroscopy Large N f QCD 36~16fund. 8 < N c f <12 N c f >12 N c f <12 Large N f two-color QCD 26, 8fund. N c f <6 - Sextet QCD 32sextet conformal conformal confinment Two-color adjoint QCD 22adjoint conformal Currently, many contradictions and little consensus
II.Lattice calculation of running coupling
Machines used - (SR11K, BG/L) - GPGPU & CPU - INSAM GPU - GPGPU, GCOE cluster - B-factory computer system
Schrödinger functional scheme Luescher, Weisz, Wolff, (’91) LuescherWeiszWolff SF coupling Standard background field Θ=0 PCAC mass=0 O(a) un-improved Wilson fermion Plaquette gauge action time (Dirichlet) space L (periodic up to exp(iθ) ） 0 L
Anomalous dimension in SF scheme to 2-loop With g FP 2 for 3-loop β-function in SF scheme, Perturbation theory Perturbation is not reliable =>Use Lattice method! Perturbative IRFP(g FP 2 ) for SU(3) gauge theory
8 & 12 flavor QCD Appelquist, Fleming, Neil, (‘08) N f = 8 N f = 12 g 2 IRFP ~ 5 consistent with PT prediction Conclusion: N f =12 is too large while N f =8 is too small. (12-flavor QCD is still under debate.)
Raw data of each L/a is close to each other. ⇒ slow running 10 flavor QCD (This work)
Step scaling function u=g 2 (L) g2g2 g02g02 L/a s×L/a Σ(u,s,a/L) Taking the continuum limit σ(u,s) = lim Σ(u,s,a/L), u=g SF 2 is not easy since O(a) improvement is not implemented Reducing discretization errors as much as possible before taking the limit is crucial. a/L→0
“ 2-loop improvement ” PACS-CS Collaboration (‘09) ‣ Use weak coupling region to estimate the two-loop improvement coefficients. ‣ “2-loop” Improved step scaling function ： Deviation at 2- loop:
Extrapolation to the continuum limit shows sign-flip before g SF 2 reaches about 10. Y. Shamir, B. Svetitsky and T. DeGrand, (‘08) Discrete beta function negativeconsistent with zeropositive
Result suggests the existence of IRFP at g FP 2 = 3.3 ~ Where is IRFP?
‣ σ P = Z P (s L) / Z P (L) ‣ Non-zero BG field ‣ For 3.3 < g 2 FP < 9.35, 0.28 < γ FP < 1.0 ! ‣ Precise value of g 2 FP is important Anomalous dimension Preliminary
Summary Lattice technique can be used to search for realistic WTC models and to see whether the long-standing (~30 yrs) problems in TC are really resolved by WTC. As a first step, we started with the study of running coupling of 10-flavor QCD to identify conformal window in SU(3) GT. The result shows an evidence of IRFP in 3.3 < g 2 FP < 9.4. ⇒ 8< N f c < < γ m < 1.0 is obtained from preliminary analysis. Pinning down γ m requires precise value of the IRFP. Next important task is to calculate S-parameter.