Overfrustrated and Underfrustrated Spin-Glasses in d=3 and 2: Evolution of Phase Diagrams and Chaos Including Spin-Glass Order in d=2

In spin-glass systems, frustration can be adjusted continuously and considerably, without changing the antiferromagnetic bond probability p, by using locally correlated quenched randomness, as we demonstrate here on hypercubic lattices and hierarchical lattices. Such overfrustrated and underfrustrated Ising systems on hierarchical lattices in d=3 and 2 are studied. With the removal of just 51 % of frustration, a spin-glass phase occurs in d=2. With the addition of just 33 % frustration, the spin-glass phase disappears in d=3. Sequences of 18 different phase diagrams for different levels of frustration are calculated in both dimensions. In general, frustration lowers the spin-glass ordering temperature. At low temperatures, increased frustration favors the spin-glass phase (before it disappears) over the ferromagnetic phase and symmetrically the antiferromagnetic phase. When any amount, including infinitesimal, frustration is introduced, the chaotic rescaling of local interactions occurs in the spin-glass phase. Chaos increases with increasing frustration, as seen from the increased positive value of the calculated Lyapunov exponent $\lambda$, starting from $\lambda =0$ when frustration is absent. The calculated runaway exponent $y_R$ of the renormalization-group flows decreases with increasing frustration to $y_R=0$ when the spin-glass phase disappears. From our calculations of entropy and specific heat curves in d=3, it is seen that frustration lowers in temperature the onset of both long- and short-range order in spin-glass phases, but is more effective on the former. From calculations of the entropy as a function of antiferromagnetic bond concentration p, it is seen that the ground-state and low-temperature entropy already mostly sets in within the ferromagnetic and antiferromagnetic phases, before the spin-glass phase is reached.Comment: Published version, 18 phase diagrams, 12 figures, 10 page

Odd q-State Clock Spin-Glass Models in Three Dimensions, Asymmetric Phase Diagrams, and Multiple Algebraically Ordered Phases

Distinctive orderings and phase diagram structures are found, from renormalization-group theory, for odd q-state clock spin-glass models in d=3 dimensions. These models exhibit asymmetric phase diagrams, as is also the case for quantum Heisenberg spin-glass models. No finite-temperature spin-glass phase occurs. For all odd $q\geqslant 5$, algebraically ordered antiferromagnetic phases occur. One such phase is dominant and occurs for all $q\geqslant 5$. Other such phases occupy small low-temperature portions of the phase diagrams and occur for $5 \leqslant q \leqslant 15$. All algebraically ordered phases have the same structure, determined by an attractive finite-temperature sink fixed point where a dominant and a subdominant pair states have the only non-zero Boltzmann weights. The phase transition critical exponents quickly saturate to the high q value.Comment: Published version, 9 pages, 10 phase diagrams, 5 figures, 1 tabl

Flavor changing neutral currents in top quark production and decay

Top quark flavor changing neutral current (FCNC) interactions are highly suppressed in the Standard Model. Therefore, any large signal of FCNCs will indicate the existence of new interactions. In this paper, searches for FCNC interactions in top quark production and decay at the Tevatron and LHC are presented. FCNC searches in $t\rightarrow qZ$ and $t\rightarrow Hq$ decays, and in top quark production in $pp\rightarrow t+j$, $pp\rightarrow t+Z$ are summarized. Effect of top quark FCNCs on single top quark cross-section, and the searches for same-sign top quark pair production through FCNCs are also described. None of the searches yielded positive results and exclusion limits on branching rations, coupling strengths and cross-sections are obtained. Future prospects of FCNC searches are also briefly discussed.Comment: 10 pages, 9 figures, To appear in the proceedings of the 6th International Workshop on Top Quark Physics (TOP 2013), Durbach, Germany, 14-19 September 201

Measurement of Top Quark Properties in Single Top Quark Production at CMS

Single top-quark t-channel production is exploited for studies of top quark properties. The analyses include the measurement of the CKM matrix element, $|V_{tb}|$, search for anomalous couplings of the top quark using a Bayesian neural network analysis, measurement of single top-quark polarization which directly confirms the V-A nature of the $tWb$ production vertex, and the measurement of W-helicity fractions in the phase space sampled by a selection optimized for t-channel single top-quark production, orthogonal to the $t\overline{t}$ final states used in traditional measurements of these properties. All measurements are found to be consistent with the standard model predictions.Comment: 6 pages, 13 figures, To appear in the proceedings of ICHEP2014: 37th International Conference on High Energy Physics, 2-9 July 2014, Valencia, Spai

Top Quark Measurements in CMS

Measurements involving top quarks provide important tests of QCD. A selected set of top quark measurements in CMS including the strong coupling constant, top quark pole mass, constraints on parton distribution functions, top quark pair differential cross sections, ttbar+0 and >0 jet events, top quark mass studied using various kinematic variables in different phase-space regions, and alternative top quark mass measurements is presented. The evolution of expected uncertainties in future LHC runs for the standard and alternative top quark mass measurements is also presented.Comment: 6 pages, 11 figures, To appear in the proceedings of QCD14: 17th High Energy International Conference in Quantum Chromodynamics, 30 Jun-4 Jul 2014, Montpellier (France

Measurements of Top Quark Properties at the LHC

Recent measurements of top quark properties at the LHC from ATLAS and CMS experiments are presented. The presented results include top quark mass, dependence of top mass measurements on event kinematics, top anti-top mass difference, bottom quark content in top quark decays, W boson polarization and anomalous couplings, search for CP violation in single top events, vector boson production associated with top-antitop pairs and top polarization.Comment: 4 pages, 3 figures, To appear in the proceedings of the 48th Rencontres de Moriond: QCD and Hadronic Interactions, La Thuile, Italy, 9-16 Mar 201

Measurements of the top-quark properties at CMS

Measurements of several top-quark properties, obtained from the CMS data collected in 2011 and 2012 at centre-of-mass energies of 7 and 8 TeV are presented. The results include measurements of the top pair charge asymmetry, the W helicity in top quark decays and the search for anomalous couplings, the top quark charge, and of the ttbar spin correlation. The fraction of top quarks decaying into a W-boson and a b-quark relative to all top quark decays, R=Br(t->Wb)/Br(t->Wq), as well as, the cross sections of ttbar events produced in association with a photon or a W or a Z boson are also presented.Comment: 5 pages, 2 figures, to appear in the proceedings of the XXI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2013), Marseille, 22-26 April 201

Top Quark Properties Measurements in CMS

Recent top quark properties measurements made with the CMS detector at the LHC are presented. The measurements summarized include spin correlation of top quark pairs, asymmetries, top quark mass, and the underlying event in top quark pair events. The results are compared to the standard model predictions and new physics models.Comment: 8 pages, 5 figures, To appear in the proceedings of LaThuile2016, Les Rencontres de Physique de la Vallee d'Aoste, March 6-12, 2016, La Thuile, Aosta Valley, Ital