DOCSLIB.ORG

Single Top Production Associated with a Neutral Scalar at LHC in Topcolor-Assisted Technicolor

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Single Top Production Associated with a Neutral Scalar at LHC in Topcolor-Assisted Technicolor Chinese Physics C (HEP & NP) Vol. 32, No. 9, Sep., 2008 Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor LIU Guo-Li(7Iw)1 ZHANG Huan-Jun(Ü)2;1) 1 (Department of Physics, Zhengzhou University, Henan 450052, China) 2 (Department of Physics, Henan Normal University, Xinxiang 453007, China) Abstract The topcolor-assisted technicolor (TC2) model predicts a number of neutral scalars like the top-pion 0 0 (πt ) and the top-Higgs (ht ). These scalars have flavor-changing neutral-current (FCNC) top quark couplings, among which the top-charm transition couplings may be sizable. Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider (LHC) through the parton ! 0 ! 0 processes cg tπt and cg tht . In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space. Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC, these rare processes will serve as a good probe for the TC2 model. Key words top quark, technicolor, LHC PACS 14.65.Ha, 12.60.Fr, 12.60.Jv As the heaviest fermion in the Standard Model ated with a neutral scalar at the LHC through the 0 0 (SM), the top quark may be a sensitive probe of new parton processes cg tπt and cg tht . In this pa- [1] ! ! physics . So far there remain plenty of room for new per we examine these productions and figure out if physics in top quark sector due to the small statis- their rates can exceed the 3σ sensitivity of the LHC. tics of the top quark events at the Fermilab Tevatron Since in the SM and the MSSM such rare produc- collider[2]. Since the upcoming Large Hadron Collider tions have unobservably small production rates at the (LHC) at CERN will produce top quarks copiously LHC, these rare processes will serve as a probe for the and allow to scrutinize the top quark nature, the new TC2 model if their TC2 predictions can be above the physics related to the top quark will be either uncov- 3σ sensitivity. ered or stringently constrained. Before our calculations we recapitulate the basics One of the properties of the top quark in the of TC2 model. The TC2 model[8] combines techni- Standard Model (SM) is its extremely small flavor- color interaction with topcolor interaction, with the changing neutral-current (FCNC)[3] interactions due former being responsible for electroweak symmetry to the GIM mechanism. Thus, the observation of breaking and the latter for generating large top quark any FCNC top quark process would be a robust evi- mass. The top quark mass is generated from two dence for new physics beyond the SM. Actually, the sources, one is from the extended technicolor (propor- FCNC top quark interactions can be significantly en- tional to ) and the other from the topcolor (propor- hanced in some new physics models, such as the popu- tional to 1 ). So the mass matrix of up-type quarks [4|6] − lar minimal supersymmetric model (MSSM) and is composed of both the extended technicolor and the the topcolor-assisted technicolor (TC2) model[7]. topcolor contributions. The diagonalization of this The TC2 model predicts a number of neutral mass matrix will induce FCNC top quark interactions scalar bosons like the top-pions and top-Higgs at the in the Yukawa couplings which involve the compos- weak scale[8]. These scalars have FCNC top couplings ite scalars respectively from topcolor and technicolor at tree-level, among which the top-charm FCNC cou- condensations. plings are most significant. Such anomalous FCNC The top-charm FCNC couplings with the top-pion couplings will induce single top productions associ- and top-Higgs can be written as[7] Received 8 November 2007 1) E-mail: [email protected] 697 | 699 698 Chinese Physics C (HEP & NP) Vol. 32 2 2 (1 )mt v Ft scale µF chosen to be µR = µF = mt + MS (MS de- FCNC = − − L p2Ft p v × notes the top-pion mass or the top-Higgs mass). tt∗ tc ¯ 0 tt∗ tc ¯ 0 The parameters involved in our calculations are (iKUL KURtLcRπt +KULKURtLcRht +h:c:); (1) the masses of the top-pions and top-Higgs, the pa- tc rameter KUR, the top-pion decay constant Ft and the where the factor v2 F 2=v (v 174 GeV) reflects − t ≈ parameter which parametrizes the portion of the the effect of the pmixing between the top-pions and extended-technicolor contribution to the top quark [9] the would-be Goldstone bosons . KUL and KUR are mass. In our numerical calculations, we take Ft = the rotation matrices that transform respectively the tt tt 50 GeV, = 0:1, KUL = 1, KUR = 0:9 and re- weak eigenstates of the left-handed and right-handed tc tain KUR as a free parameter with a value less than up-type quarks to their mass eigenstates, which can p2 2 = 0:43. The top quark mass is taken as [7] − [2] be parametrized as mt = 170:9 GeV . 0 tt tt mt For the masses of the neutral top-pion and top- KUL 1; KUR mt = 1 , ≈ ≈ − (2) Higgs, current constraints are rather weak. Theoret- tc tt 2 2 KUR 6 1 (KUR) = p2 ; ically the top-pion masses are model-dependent and − − [8] 0 p are usually of a few hundred GeV . The top-Higgs with m denoting the topcolor contribution to the top t mass, as analysed in Ref. [7], has a lower bound of quark mass. In Eq. (1) we neglected the mixing be- about 2m , which however is an approximate analy- tween up quark and top quark. t sis and the mass below t¯t threshold is also possible[11]. As shown in Fig. 1, these FCNC interactions in Experimentally, the neutral top-pion mass can be Eq. (1) induce single top productions associated with constrained if we assume the degeneracy of neutral a top-pion or a top-Higgs at the LHC through the and charged top-pion masses (the mass splitting be- parton processes cg tπ0 or cg th0. The ampli- ! t ! t tween the neutral top-pion and the charged top-pion tude for cg tπ0 is given by ! t comes only from the electroweak interactions and 2 2 1 mt v Ft tt∗ tc thus should be small). The charged top-pion mass is = gs − KURKURu¯t + M − p2 Ft p v × constrained from the absence of t πt b, which gives [12] ! a lower bound of 165 GeV , and also from Rb data, 1 µ 1 µ (p + p )γ + γ (p p +m ) P u ; [13] s^ 6 c 6 g u^ m2 6 t− 6 g t R c which yields a lower bound of about 250 GeV . In − t (3) our numerical results we will show the dependence on the masses of neutral top-pion and top-Higgs. where PR = (1+γ5)=2, and pt;c;g are the momenta of In the following we present some results for the top quark, charm quark and gluon, respectively. hadronic production cross section via cg tπ0. These ! t results are also applicable to the production through cg th0, with the top-pion mass replaced by the ! t top-Higgs mass. Fig. 2. Hadronic cross section for the produc- ! 0 Fig. 1. Feynman diagrams for parton-level pro- tion via cg tπt at the LHC versus the top- ! 0 ! 0 pion mass. cess cg tπt and cg tht . Figure 2 shows that the hadronic cross section ver- tc The hadronic cross section at the LHC is obtained sus the top-pion mass for different values of KUR. We by convoluting the parton cross section with the par- see that the cross section increases with the increasing tc ton distribution functions. In our calculations we use KUR since the cross section is simply proportional to [10] tc 2 CTEQ6L to generate the parton distributions with (KUR) as shown in Eq. (3). As the top-pion mass in- the renormalization scale µR and the factorization creases, the cross section decreases. The cross section No. 9 LIU Guo-Li et alµSingle top production associated with a neutral scalar at LHC in topcolor-assisted technicolor 699 is about several hundreds fb in most of the parameter also inaccessible at the LHC. So these rare processes space. will serve as a good probe for the TC2 model. Due to the large QCD backgrounds at the LHC, for the productions of PP tφ0 + X (φ0 is a neu- ! tral scalar and can be top-pion or top-Higgs) we search for the final states from the subsequent decays t Wb `νb (` = e;µ) and φ0 bb.¯ So the main ! ! ! SM background is the production of t¯t and Wbb¯jj, where one light jet is mis-identified as a b-jet while the other light jet is not detected if it goes along the pipeline or its transverse momentum is too small. The observability of the signal at the LHC has been investigated in the effective Lagrangian approach[14]. Assuming a luminosity of 100 fb−1, we know from Table 2, Table 4 and Eq. (4) in Ref. [14] Fig. 3. The contour of 3σ sensitivity (200 fb) that the 3σ sensitivity for the production of PP ! for the cross section of the production via φ0 ! 0 Ktc t + X is about 200 fb. Although this sensitivity is cg tπt at the LHC in the plane of UR based on the effective Lagrangian approach and may versus the top-pion mass.
Load more

Recommended publications
  • ``Topcolor''; Invited Talk Presented At" Strongly Coupled Gauge Theories
    FERMILAB-Conf-97/032-T TOPCOLOR1 CHRISTOPHER T. HILL Fermi National Accelerator Laboratory P.O. Box 500, Batavia, Illinois, 60510, USA We review a class of dynamical models in which top condensation occurs at the weak scale, giving rise to the large top quark mass and other phenomena. This typically requires a color embedding, SU(3) SU(3)1 SU(3)2, ergo “Topcolor.” Topcolor suggests c → × a novel route to technicolor models in which sequential quarks condense under the Topcolor interaction to break electroweak symmetries. 1 Top Quark Condensation 1.1 Preliminary The top quark has arrived with a mass of 175 GeV. This is remarkably ∼ large in comparison to all other known fundamental particles, and coin- cidently equals the natural scale of electroweak interactions, 1/ 2√2GF . The top quark mass may be dynamically generated, analogousq to a con- stituent quark mass in QCD. Then the relevant question becomes: “Are arXiv:hep-ph/9702320v1 12 Feb 1997 there new strong interactions that are revealing themselves through the large top mass?” If the answer is no, then the most sensible scenario for physics beyond the standard model is something like the minimal supersymmetric standard model (MSSM). In this case the top quark mass is given by the infra–red renormalization group fixed point [1], and many of the successful predictions of unification are tied to this fact [2]. By itself, this is remarkable, because the infra–red renormalization group fixed point is really a consequence of the approximate scale invariance of the unified theory over the range of 1Invited Talk presented at Strongly Coupled Gauge Theories ‘96, Nagoya, Nov.
    [Show full text]
  • Two Composite Higgs Doublets: Is It the Low Energy Limit of A
    Two Composite Higgs Doublets: Is it the Low Energy Limit of a Natural Strong Electroweak Symmetry Breaking Sector ? Alfonso R. Zerwekh∗ Centro de Estudios Subat´omicos and Instituto de F´ısica, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia,Chile Abstract In this paper, we propose an effective model scheme that describes the electroweak symmetry breaking sector by means of composite Higgs- like scalars, following the ideas of Minimal Walking Technicolor (MWT). We argue that, because of the general failure of Extended Technicolor (ETC) to explain the mass of the top quark, it is necessary to introduce two composite Higgs bosons: one of them originated by a MWT-ETC sector and the other one produced by a Topcolor sector. We focus on the phenomenological differences between the light composite Higgs present in our model and the fundamental Higgs boson predicted by the Standard Model and their production at the LHC. We show that in this scheme the main production channel of the lighter Higgs boson are the associated production with a gauge boson and WW fusion but not the gluon-gluon fusion channel which is substantially suppressed. 1 Introduction arXiv:0907.4690v3 [hep-ph] 25 Dec 2009 High Energy Physics is at the dawn of a new era. In the very near future the LHC will allow us to explore, for the first time, the physics responsible for the electroweak symmetry breaking. We are quite sure that something different to the minimal Higgs sector of the Standard Model will be found, but the conjectured alternatives, far from being unique, are varied and very different among them, going from Higgsless models to Supersymmetry.
    [Show full text]
  • Higgs Bosons Strongly Coupled to the Top Quark
    CERN-TH/97-331 SLAC-PUB-7703 hep-ph/9711410 November 1997 Higgs Bosons Strongly Coupled to the Top Quark Michael Spiraa and James D. Wellsb aCERN, Theory Division, CH-1211 Geneva, Switzerland bStanford Linear Accelerator Center Stanford University, Stanford, CA 94309† Abstract Several extensions of the Standard Model require the burden of electroweak sym- metry breaking to be shared by multiple states or sectors. This leads to the possibility of the top quark interacting with a scalar more strongly than it does with the Stan- dard Model Higgs boson. In top-quark condensation this possibility is natural. We also discuss how this might be realized in supersymmetric theories. The properties of a strongly coupled Higgs boson in top-quark condensation and supersymmetry are described. We comment on the difficulties of seeing such a state at the Tevatron and LEPII, and study the dramatic signatures it could produce at the LHC. The four top quark signature is especially useful in the search for a strongly coupled Higgs boson. We also calculate the rates of the more conventional Higgs boson signatures at the LHC, including the two photon and four lepton signals, and compare them to expectations in the Standard Model. CERN-TH/97-331 SLAC-PUB-7703 hep-ph/9711410 November 1997 †Work supported by the Department of Energy under contract DE-AC03-76SF00515. 1 Introduction Electroweak symmetry breaking and fermion mass generation are both not understood. The Standard Model (SM) with one Higgs scalar doublet is the simplest mechanism one can envision. The strongest arguments in support of the Standard Model Higgs mechanism is that no experiment presently refutes it, and that it allows both fermion masses and electroweak symmetry breaking.
    [Show full text]
  • Model-Independent Constraints on Topcolor from Rb
    MADPH-97-984 TUM-HEP-267/97 hep-ph/9702265 Model-independent Constraints on Topcolor from Rb Gustavo Burdman∗ Department of Physics, University of Wisconsin, Madison, WI 53706, USA and Dimitris Kominis† Institut f¨ur Theoretische Physik, Technische Universit¨at M¨unchen, James-Franck-Straße, 85748 Garching, Germany Abstract arXiv:hep-ph/9702265v2 8 May 1997 We identify and compute the main corrections to Rb in Topcolor theories. They are due to the top-pions, the pseudo-Goldstone bosons associated with the chiral symmetry breaking responsible for the top quark mass, and amount to (1 4)%, − − independent of the details of the Topcolor model. We show that the cancellation of this effect against the contributions from Topcolor vector and scalar resonances is unlikely, given the inherently distinct character of the two scales governing the potentially cancelling terms. The resulting value of Rb leads to severe constraints on Topcolor theories. ∗e-mail address: [email protected] †e-mail address: [email protected] 1 Introduction The large value of the top-quark mass has led to speculation that the properties of the top quark may be fundamentally different from those of the other known fermions. In theories of top condensation, for example, a new strong gauge interaction (Topcolor), which couples to the t-quark and perhaps to other fermions as well, drives the formation of a tt¯ condensate and imparts a large dynamical mass to the top quark. In the process, h i the chiral symmetries associated with the strongly interacting fermions are spontaneously broken and at least three Goldstone bosons emerge.
    [Show full text]
  • Outlook Post-Higgs
    Outlook Post-Higgs Christopher T. Hill Fermilab UCLA Higgs Workshop March 22, 2013 A dynamical “Higgs” mechanism was supposed to explain the origin of electroweak mass A dynamical “Higgs” mechanism was supposed to explain the origin of electroweak mass We now know that, evidently, a fundamental Higgs Boson exists and explains the masses of quarks, leptons, W and Z A dynamical “Higgs” mechanism was supposed to explain the origin of electroweak mass We now know that, evidently, a fundamental Higgs Boson exists and explains the masses of quarks, leptons, W and Z The Higgs Boson does NOT explain the origin of the electroweak mass-scale A dynamical “Higgs” mechanism was supposed to explain the origin of electroweak mass We now know that, evidently, a fundamental Higgs Boson exists and explains the masses of quarks, leptons, W and Z The Higgs Boson does NOT explain the origin of the electroweak mass-scale i.e., what is the origin of the Higgs Boson mass itself? A dynamical “Higgs” mechanism was supposed to explain the origin of electroweak mass We now know that, evidently, a fundamental Higgs Boson exists and explains the masses of quarks, leptons, W and Z The Higgs Boson does NOT explain the origin of the electroweak mass-scale i.e., what is the origin of the Higgs Boson mass itself? This may present opportunities for a deeper understanding QCD beautifully explains the origin of strong mass : The magnificent scale anomaly: The scale current: = 0 in a scale invariant theory The magnificent scale anomaly: The scale current: = 0 in a scale invariant
    [Show full text]
  • Symmetry Breaking and Generational Mixing in Topcolor--Assisted
    BUHEP–96–2 hep-ph/9602221 Symmetry Breaking and Generational Mixing in Topcolor–Assisted Technicolor Kenneth Lane† Department of Physics, Boston University 590 Commonwealth Avenue, Boston, MA 02215 Abstract Topcolor–assisted technicolor provides a dynamical explanation for electroweak and flavor symmetry breaking and for the large mass of the top quark without unnatural fine tuning. A major challenge is to generate the observed mixing between heavy and light generations while breaking the strong topcolor interactions near 1 TeV. I argue that these phenomena, as well as electroweak symmetry breaking, are intimately connected and I arXiv:hep-ph/9602221v1 4 Feb 1996 present a scenario for them based on nontrivial patterns of technifermion condensation. I also exhibit a class of models realizing this scenario. This picture leads to a rich phe- nomenology, especially in hadron and lepton collider experiments in the few hundred GeV to few TeV region and in precision electroweak tests at the Z0, atomic parity violation, and polarized Møller scattering. 2/96 † [email protected] 1. Introduction Topcolor–assisted technicolor (TC2) was proposed by Hill [1] to overcome major shortcomings of top–condensate models of electroweak symmetry breaking [2], [3] and of technicolor models of dynamical electroweak and flavor symmetry breaking [4], [5]. Technicolor and extended technicolor (ETC) have been unable to provide a natural and plausible understanding of why the top quark mass is so large [6]. On the other hand, models in which strong topcolor interactions drive top–quark condensation and elec- troweak symmetry breaking are unnatural. To reproduce the one–Higgs–doublet standard model consistent with precision electroweak measurements (especially of the parameter 2 2 2 ρ = M /M cos θW 1), the topcolor energy scale must be much greater than the W Z ≃ electroweak scale of (1 TeV).
    [Show full text]
  • Anatomy of Top-Mode Extended Technicolor Model
    December 9, 2018 Anatomy of Top-Mode Extended Technicolor Model ∗ Hidenori Fukano† and Koichi Yamawaki‡ Department of Physics, Nagoya University Nagoya 464-8602, Japan Abstract We analyze two versions of the extended technicolor (ETC) incorporating the top quark condensate via the flavor-universal coloron type topcolor SU(3) 1 × SU(3)2: A straightforward top-mode ETC having quarks and techniquarks as- signed to a single (strong) SU(3)1, and a “twisted model” with techniquarks carrying the weak SU(3)2 while quarks the strong SU(3)1. The straightforward model has the same ETC structure as that of Appelquist et al. without top- color which we first analyze to find that it yields only too small ETC-induced mass for the third generation. In contrast, our model having topcolor takes the form of a version of the topcolor-assisted technicolor (TC2) after ETC breakings, which triggers the top quark condensate giving rise to a realistic top mass. How- ever, techniquarks have the strong topcolor SU(3)1 in addition to the already strong walking/conformal technicolor, which triggers the techniquark condensate arXiv:0801.3716v2 [hep-ph] 19 Feb 2008 at scale much higher than the weak scale, a disaster. We then consider a “twisted model” of TC2, though not an explicit ETC. We find a new feature that “ETC”- induced quark mass is enhanced to the realistic value by the large anomalous dimension γ 2 of Nambu-Jona-Lasinio-type topcolor interactions. The result m ≃ roughly reproduces the realistic quark masses. We further find a novel effect of the above large anomalous dimension γ 2: The top-pion mass has a universal m ≃ upper bound, mπt < 70 GeV, in the generic TC2 model.
    [Show full text]
  • Search for Top Quark Pair Resonances with the CMS Detector at the LHC
    Search for Top Quark Pair Resonances with the CMS Detector at the LHC Von der Fakult¨atf¨urMathematik, Informatik und Naturwissenschaften der RWTH Aachen University zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigte Dissertation vorgelegt von Wael Haj Ahmad aus Edlib/Syrien Berichter: Univ.-Prof. Dr.rer.nat. Achim Stahl Univ.-Prof. Dr.rer.nat. Thomas Hebbeker Tag der m¨undlichen Pr¨ufung:29.05.2013 Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verf¨ugbar. Contents Contents vi Abstract vii Zusammenfassung ix 1 Overview 1 1.1 Introduction . .1 1.2 The Standard Model of Particle Physics (SM) . .2 1.3 The Top Quark . .4 1.3.1 Top Quark Pair Production . .4 1.3.2 Top Quark Decay Channels . .7 1.4 Top Quark Pair Resonances . .8 1.4.1 Topcolor Assisted Technicolor Z0 ............9 2 The CMS Detector at the LHC 13 2.1 The Large Hadron Collider . 13 2.2 The CMS Detector . 17 2.2.1 The CMS Requirements . 18 2.2.2 The CMS Coordinates . 20 2.2.3 The CMS Inner Tracking System . 21 2.2.4 The Electromagnetic Calorimeter . 22 iv CONTENTS 2.2.5 The Hadronic Calorimeter . 24 2.2.6 The Superconducting Magnet . 26 2.2.7 The Muon System . 26 2.2.8 The Trigger System . 28 3 Object Identification and Reconstruction 31 3.1 Reconstruction of Tracks . 32 3.2 Reconstruction of Primary Vertices . 35 3.3 Reconstruction and Identification of Muons . 37 3.3.1 Reconstruction of Muons . 37 3.4 Reconstruction of Electrons .
    [Show full text]
  • Probing Topcolor-Assisted Technicolor from Top-Charm Associated Production at LHC
    Probing Topcolor-Assisted Technicolor from Top-Charm Associated Production at LHC Junjie Caoa;b, Zhaohua Xiong c, Jin Min Yang b a CCAST (World Laboratory), P.O.Box 8730, Beijing 100080, China b Institute of Theoretical Physics, Academia Sinica, Beijing 100080, China c Graduate School of Science, Hiroshima University, Hiroshima 937-6256, Japan (April 2, 2003) tc bb + +√2KUR∗ KDLc¯RbLπt + h:c: ; (1) We propose to probe the topcolor-assisted technicolor i (TC2) model from the top-charm associated productions at where v 174 GeV, F 50 GeV is the top-pion decay the LHC, which are highly suppressed in the Standard Model. t constant' and the factor' v2 F 2=v reflects the effect Due to the flavor-changing couplings of the top quark with − t the scalars (top-pions and top-Higgs) in TC2 model, the of the mixing between thep top-pions and the would-be top-charm associated productions can occur via both the s- goldstone bosons [8]. KUL, KDL and KUR are the rota- channel and t-channel parton processes by exchanging a scalar tion matrices that transform the weak eigenstates of left- field at the LHC. We examined these processes through Monte handed up-type, down-type and right-handed up-type Carlo simulation and found that they can reach the observ- quarks to the mass eigenstates, respectively. As pointed able level at the LHC in quite a large part of the parameter tc out in [6], the transition between tR and cR, KUR,canbe space of the TC2 model. naturally around 10% 30% without conflict with low energy experimental data∼ and Ks can be parameterized 14.65.Ha, 12.60.Fr, 12.60.Jv as follows: Ktt = Kbb =1;Ktt =1 , The fancy idea of technicolor (TC) provides a possi- UL DL DR − ble mechanism of breaking the electroweak symmetry dy- tc tt 2 tu 2 2 KUR = 1 KUR KUR 2 ; (2) namically.
    [Show full text]
  • Is the Higgs Boson Composed of Neutrinos?
    Is the Higgs Boson Composed of Neutrinos? Jens Krog1, ∗ and Christopher T. Hill2, y 1CP3-Origins, University of Southern Denmark Campusvej 55, 5230 Odense M, Denmark 2Fermi National Accelerator Laboratory P.O. Box 500, Batavia, Illinois 60510, USA (Dated: January 16, 2020) We show that conventional Higgs compositeness conditions can be achieved by the running of large Higgs-Yukawa couplings involving right-handed neutrinos that become active at ∼ 1013 − 1014 GeV. Together with a somewhat enhanced quartic coupling, arising by a Higgs portal interaction to a dark matter sector, we can obtain a Higgs boson composed of neutrinos. This is a "next-to-minimal" dynamical electroweak symmetry breaking scheme. PACS numbers: 14.80.Bn,14.80.-j,14.80.Da I. INTRODUCTION treatment indicates that a tt composite Higgs boson re- quires (i) a Landau pole at scale Λ in the running top HY Many years ago it was proposed that the top quark coupling constant, yt(µ), (ii) the Higgs-quartic coupling λH must also have a Landau pole, and (iii) compositeness Higgs-Yukawa (HY) coupling, yt, might be large and 4 conditions must be met, such as λH (µ)=gt (µ) ! 0 and governed by a quasi-infrared-fixed point behavior of the 2 renormalization group [1, 2]. This implied, using the min- λH (µ)=gt (µ) !(constant) as µ ! Λ, [5]. This predicts a imal ingredients of the Standard Model, a top quark mass Higgs boson mass of order ∼ 250 GeV with a heavy top quark of order ∼ 220 GeV, predictions that come within of order 220−240 GeV for the case of a Landau pole in yt at a scale, Λ, of order the GUT to Planck scale.
    [Show full text]
  • Top Condensation As a Motivated Explanation of the Top Forward-Backward Asymmetry
    Top Condensation as a Motivated Explanation of the Top Forward-Backward Asymmetry The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Cui, Yanou, Zhenyu Han, and Matthew Schwartz. 2011. Top condensation as a motivated explanation of the top forward- backward asymmetry. Journal of High Energy Physics 2011(7): 127. Published Version doi:10.1007/JHEP07(2011)127 Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:8160982 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#OAP Top condensation as a motivated explanation of the top forward-backward asymmetry Yanou Cui, Zhenyu Han, and Matthew D. Schwartz Center for the Fundamental Laws of Nature Harvard University, Cambridge, MA 02138, USA Abstract Models of top condensation can provide both a compelling solution to the hierarchy problem as well as an explanation of why the top-quark mass is large. The spectrum of such models, in particular topcolor-assisted technicolor, includes top-pions, top-rhos and the top-Higgs, all of which can easily have large top-charm or top-up couplings. Large top-up couplings in particular would lead to a top forward-backward asymmetry through t-channel exchange, easily consistent with the Tevatron measurements. Intriguingly, there is destructive interference between the top- mesons and the standard model which conspire to make the overall top pair production rate consistent with the standard model.
    [Show full text]
  • Probing Top Quark Polarization Effects in Topcolor-Assisted Technicolor Model
    1 31 ò 1 11 Ï p U Ô n Ø Ô n Vol. 31, No. 11 2007 c 11 HIGH ENERGY PHYSICS AND NUCLEAR PHYSICS Nov., 2007 Probing Top Quark Polarization Effects in Topcolor-Assisted Technicolor Model * GU Qin-Zhong1;2;1) JIANG Feng-Chun3 WANG Xue-Lei2 YANG Hua4 1 (Shangqiu Teachers College, Shangqiu 476000, China) 2 (Henan Normal University, Xinxiang 453007, China) 3 (Zhengzhou University of Light Industry, Zhengzhou 450002, China) 4 (Information Engineering University, Zhengzhou 450004, China) Abstract We study the polarization effects of the top-quark on the t¯t production cross sections at hadron colliders in the topcolor-assisted technicolor model . The MRS set A0 parton distributions and the helicity projection operators methods are used in the calculation. It is shown that the polarization effects of the top quark are too small to produce enough identified signals at the Tevatron while they can be large enough to be detected at the LHC with reasonable values of the parameters. The polarization effects at the LHC can reach 16%, therefore, they provide feasible tests of the topcolor-assisted technicolor model. Key words topcolor-assisted technicolor model, electroweak symmetry breaking, polarization 1 Introduction a center-of-mass energy (c.m.) 2TeV, which is now engaged in RUN II, has the significant potential to So far, the most unclear part of the Standard discover a light Higgs boson with mass up to about Model (SM) is its symmetry breaking sector. Study- Mh 6 130GeV in the SM or MSSM. However, it will ing the electroweak symmetry breaking (EWSB) have very little capability to determine the overarch- mechanism will be one of the most important tasks ing model that governs the EWSB if a Higgs or Higgs- in particle physics.
    [Show full text]