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Register a new userFlavor-singlet spectrum in multi-flavor QCD
تدرج الذوق الوحيد في QCD المتعدد الأذواق
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إن الدراسة في النظم المقياس SU(3) مع زيادة عدد الفرميونات الخفيفة ذات صلة بالشأن الذي يتعلق بتحليل ديناميكي القوي ل QCD وببناء امتدادات تفاعلية قوية لنموذج المعيار (مثل اكمال UV لنماذج الهيجس المركبة). للتباين من هذه النظم التفاعلية التي تحتوي على العديد من النكهات، نحن ندرس المذبذب الوحيد النكهة كمستقبل مثير للاهتمام. في الواقع، بعض نماذج الهيجس المركبة تتطلب أن يكون الهيجس أصغر سكالار في المذبذب الوحيد النكهة في المذبذب الذي يحتوي على هرم بين الدوال المتبقية من القطاع الجديد الذي يتفاعل قويا. بالإضافة إلى ذلك، يمكن أن تؤثر إدخال العديد من النكهات الخفيفة على عدد محدد من الألوان على ديناميكي الأصغر سكالار الوحيد النكهة. نقدم الدراسة الجارية لهذه القنوات الوحيدة النكهة باستخدام معالجي التقاط المتعددة على أجيال عالية الإحصائية التي تم إنشاؤها من قبل مشاركة LatKMI ونقارن النتائج مع البيانات المتوفرة التي تم الحصول عليها من قبل مشاركة الحد القوي اللاطيق. للنظام الذي يحتوي على 8 نكهات، قامت المشاركتان بإنشاء التكوينات التي تتناسب مع بعضها البعض مع الغرض من التعامل مع الحد الصفري باستخدام أكبر قياسات ممكنة.
Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.
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We report the calculation of the flavor-singlet scalar in the SU(3) gauge theory with the degenerate twelve fermions in the fundamental representation using a HISQ-type action at a fixed $beta$. In order to reduce the large statistical error coming from the vacuum-subtracted disconnected correlator, we employ a noise reduction method and a large number of configurations. We observe that the flavor-singlet scalar is lighter than the pion in this theory from the calculations with the fermion bilinear and gluonic operators. This peculiar feature is considered to be due to the infrared conformality of this theory, and it is a promissing signal for a walking technicolor, where a light composite Higgs boson is expected to emerge by approximate conformal dynamics.
We present results for the mass of the eta-prime meson in the continuum limit for two-flavor lattice QCD, calculated on the CP-PACS computer, using a renormalization-group improved gauge action, and Sheikholeslami and Wohlerts fermion action with tadpole-improved csw. Correlation functions are measured at three values of the coupling constant beta corresponding to the lattice spacing a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams are evaluated using a noisy source method. We calculate eta-prime propagators using local sources, and find that excited state contributions are much reduced by smearing. A full analysis for the smeared propagators gives metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.
The hadron spectrum of one flavor QCD is studied by Monte Carlo simulations. The Symanzik tree-level-improved Wilson action is used for the gauge field and the Wilson action for the fermion. The theory is simulated by a polynomial hybrid Monte Carlo algorithm (PHMC). The mass spectrum of hadronic bound states is investigated at two different lattice spacings: a ~ 0.37r_0 and a ~ 0.27r_0, corresponding to ~0.19fm and ~0.13fm in ordinary QCD. The lattice extension is fixed to L ~ 4.4r_0 (~2.2fm). The lightest simulated quark mass corresponds to a pion with mass ~270MeV. Properties of the theory are analyzed by making use of the ideas of partially quenched chiral perturbation theory (PQChPT). The symmetry of the single flavor theory can be artificially enhanced by adding extra valence quarks, which can be interpreted as u and d quarks. Operators in the valence pion sector can be built. Masses and decay constants are analyzed by using PQChPT formulae at next-to-leading order.
The latest results of an ongoing project for the lattice simulation of QCD with a single quark flavor are presented. The Symanzik tree-level-improved Wilson action is adopted in the gauge sector and the (unimproved) Wilson action for the fermion. Results from new simulations with one step of Stout-smearing (rho=0.15) in the fermion action are discussed. The one-flavor theory is simulated by a polynomial hybrid Monte Carlo algorithm (PHMC) at beta=4.0 corresponding to a = 0.13fm, on 16^3x32 and 24^3x48 lattices; the box-size is L = 2.1fm and L = 3.1fm, respectively. At the lightest simulated quark mass the (partially quenched) pion mass is ~300 MeV. The masses of the lightest bound states are computed, including the flavor singlet scalar and pseudoscalar mesons sigma_s and eta_s, the scalar glueball 0^++, and the Delta^++ baryon. Relics of SUSY in the mass spectrum, expected from a large N_c orientifold equivalence with the N=1 supersymmetric Yang-Mills theory, are discussed.
CP-PACS and JLQCD collaborations are carrying out a joint project of the 2+1 flavor full QCD simulation. Gauge configurations are generated for the non-perturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action using PHMC algorithm at three lattice spacings, $asim 0.076$, 0.010 and 0.122 fm, with a fixed physical volume $(2.0 fm)^3$. We present analysis for the light meson spectrum and quark masses in the continuum limit, which are determined using data obtained from the simulations at the two coarser lattices. Our simulations reproduce experimental values of meson masses. The ud and strange quark masses turn out to be $m_{ud}^{bar{MS}}(mu=2 GeV)=3.34(23) MeV$ and $m_s^{bar{MS}}(mu=2 GeV)=86.7(5.9) MeV$. We also show preliminary results at our finest lattice spacing for which simulations are still being continued.
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