New physics at a high scale Lambda can affect top-related observables at O(1/Lambda^2) via the interference of effective four quark operators with the SM amplitude. The (\bar{u} gamma_mu gamma^5 T^a u)(\bar{t} gamma^mu gamma^5 T^a t) operator modifies the large M_{t\bar{t}} forward-backward asymmetry, and can account for the recent CDF measurement. The (\bar{u} gamma_mu T^a u)(\bar{t} gamma^mu T^a t) operator modifies the differential cross section, but cannot enhance the cross section of ultra-massive boosted jets by more than 60%. The hint for a larger enhancement from a recent CDF measurement may not persist future experimental improvements, or may be a QCD effect that is not accounted for by leading order and matched Monte Carlo tools or naive factorization. If it comes from new physics, it may stem from new light states or an O(1/Lambda^4) new physics effect.
The CDF collaboration recently reported an upper limit on boosted top pair production and noted a significant excess above the estimated background of events with two ultra-massive boosted jets. We discuss the interpretation of the measurement and its fundamental implications. In case new physics is involved, the most naive contribution is from a new particle produced with a cross section that is a few times higher than that of the top quark and a sizable hadronic branching ratio. We quantify the resulting tension of a possible larger top pair cross section with the absence of excess found in …
The CDF collaboration has recently reported a large deviation from the standard model of the t \bar t forward-backward asymmetry in the high invariant mass region. We interpret this measurement as coming from new physics at a heavy scale Lambda, and perform a model-independent analysis up to O(1/Lambda^4). A simple formalism to test and constrain models of new physics is provided. We find that a large asymmetry cannot be accommodated by heavy new physics that does not interfere with the standard model. We show that a smoking gun test for the heavy new physics hypothesis is a significant deviat…
A color-singlet neutral vector boson is considered as a possible common origin of the top forward-backward asymmetry and the CDF dijet resonance. We identify chiral and flavor structures of the couplings of this new vector boson to the standard model quarks for which one could accommodate both data. We also demonstrate that non-vanishing observables involving longitudinal top polarizations can provide useful criteria for the possible existence of parity violating new physics in the q q^bar -> t t^bar process, and discrimination between the flavor-conserving and flavor-violating cases.
We construct anomaly-free leptophobic U(1)' flavor models with light Z'(~ 145 GeV). In order to allow renormalizable Yukawa interactions for the standard model chiral fermions, new Higgs doublets with nonzero U(1)' charges are introduced. Then the neutral (pseudo)scalar Higgs bosons as well as Z' contribute to the t\bar{t} and the same sign top pair productions [σ(t\bar{t}]) and σ(tt)], and one can evade the strong constraint from σ(tt). The top forward-backward asymmetry (A_{FB}) and Wjj excess at CDF could be accommodated by A_{FB}^{New} = 0.084 ~ 0.12 and σ(W j j) \lesssim O(10) pb \times \…
Predictions are made for the forward-backward and charge asymmetries in bottom-quark pair production at hadron colliders. Tree-level exchanges of electroweak (EW) gauge bosons dominate the Standard Model (SM) contribution to the asymmetry near the $Z$-pole. The mixed EW-QCD corrections are computed in an approximate way, and are found to be small in magnitude. These SM predictions are consistent with experimental results from CDF, D0, and LHCb. In particular, CDF and LHCb find that the asymmetry in the invariant mass bin containing the $Z$-pole is larger than in the adjacent bins, as predicted…
The new physics required to explain the anomalies recently reported by the D0 and CDF collaborations, namely the top forward-backward asymmetry (FBA), the like-sign dimuon charge asymmetry in semileptonic b decay, and the CDF dijet excess, has to feature an amount of flavor symmetry in order to satisfy the severe constrains arising from flavor violation. In this paper we show that, once baryon number conservation is imposed, color & weak triplet scalars with hypercharge $Y=1/3$ can feature the required flavor structure as a consequence of standard model gauge invariance. The color & weak tripl…
We present a simple, perturbative, and renormalizable model with a flavor symmetry which can explain both the t-tbar forward-backward asymmetry and the bump feature present in the dijet mass distribution of the W+jj sample in the range 120-160 GeV that was recently reported by the CDF collaboration. The flavor symmetry not only ensures the flavor/CP safety of the model, but also relates the two anomalies unambiguously. It predicts a comparable forward-backward asymmetry in c-cbar. The forward-backward asymmetry in b-bar is, however, small. A bump in the dijet mass distribution in Z+jj sample i…
Recently the CDF and the D0 Collaborations presented the data on the top forward-backward (FB) asymmetry A_FB as functions of M_(t t^bar) and Δy = y_t - y_t^bar. We study these observables in the effective Lagrangian approach with dimension-6 q q^bar t t^bar contact interactions, and compare with the CDF and D0 data. When we stay within the validity region of the effective Lagrangian approach, the mass dependent top FB asymmetry turns out to be smaller than the CDF data, more than 2-sigma away. If this discrepancy remains in the future data with better statistics, it would imply that the effec…
Recently Nelson et al. proposed an interesting flavor symmetric model to account for the top quark forward-backward asymmetry and the dijet anomaly at CDF simultaneously with just three parameters: a coupling constant of order one, and two scalar masses of 160 GeV and 220 GeV. However these fiducial values of the parameters lead to the branching ratio of a almost pure penguin B -> pi K decay about one hundred times larger than the experimental results. Consider also the precision electroweak constraints, the scalar masses should be at least around 500 GeV. Actually with the coupling constant l…
Recent CDF and D0 measurements of the top quark forward-backward asymmetry at the Tevatron present deviations between 1-sigma and 2-sigma from QCD predictions and a cut M_inv > 450 GeV on the events increases this deviation to 3.4 sigma in the CDF measurement. The inclusion of electroweak contributions of order alpha^2 and order alpha alphas^2 enlarges the theoretical prediction from QCD by a factor ~ 1.2 and diminishes the observed deviations. The calculation method is shortly discussed and numerical results are compared to the experimental data.
The recent forward-backward asymmetry recorded by the CDF Collaboration for the top and anti-top quark pair production indicates more than $2σ$ deviation from the Standard Model prediction, while its total production cross section remains consistent. We propose a $W'$ boson that couples to down and top quarks. We identify the parameter space that can give rise a large enough forward-backward asymmetry without producing too many top and anti-top quark pairs. Other models presented erstwhile in the literature that can produce such effects are also discussed.
We consider a model that includes light colored scalars from the {\bf 45} and {\bf 50} representations of SU(5) in order to explain the CDF- and D$Ø$-reported $t\bar{t}$ forward-backward asymmetry, $A^{t\bar{t}}_{FB}$. These light scalars are, labeled by their charges under the Standard Model gauge groups, the $(6,1)_{4/3}$ and $(\bar{6},3)_{1/3}$ from the {\bf 50} and the $(8,2)_{1/2}$ from the {\bf 45}. When the Yukawa coupling of the {\bf 50} is reasonably chosen and that of the {\bf 45} kept negligible at the scale of $M_Z$, the model yields phenomenologically viable results in agreement w…
We determine the dominant missing Standard Model (SM) contribution to the top quark pair forward-backward asymmetry at the Tevatron. Contrary to past expectations, we find a large, around 27%, shift relative to the well-known value of the inclusive asymmetry in next-to-leading order (NLO) QCD. Combining all known Standard Model corrections, we find that AFB^{SM} = 0.095 +- 0.007. This value is in agreement with the latest D0 measurement [V. M. Abazov et al. (D0 Collaboration), Phys. Rev. D 90, 072011 (2014)] AFB^{D0} = 0.106+- 0.03 and about 1.5 sigma below that of CDF [T. Aaltonen et al. (CDF…
Very recently, it has been shown by other authors that the CDF measurement of the top quark forward-backward asymmetry can be explained by means of a heavy and broad axigluon. In order to work, this mechanism needs that the axigluon coupling to the top quark must be different than the coupling to light quarks and both must be stronger than the one predicted in classical axigluon models. In this paper, we argue that this kind of axigluon can be accommodated in an extended chiral color model we proposed previously. Additionally, we show that the desired features can be derived from a simple four…
The CDF and LHCb experiments have recently provided two intriguing hints for new physics: a large forward-backward asymmetry in $t\bar t$ production, and a direct CP asymmetry in D decays of order a percent. In both cases, flavor non-universal interactions are required in the up sector, raising the possibility that the two effects come from one and the same new physics source. We show that a minimal model, with an extra scalar doublet, previously suggested to explain the top data, gives -- without any modifications or additions -- a contribution to CP violation in charm decays that is of the r…
A large forward-backward asymmetry in $t\bar t$ production, for large invariant mass of the $t\bar t$ system, has been recently observed by the CDF collaboration. Among the scalar mediated mechanisms that can explain such a large asymmetry, only the t-channel exchange of a color-singlet weak-doublet scalar is consistent with both differential and integrated $t\bar t$ cross section measurements. Constraints from flavor changing processes dictate a very specific structure for the Yukawa couplings of such a new scalar. No sizable deviation in the differential or integrated $t\bar t$ production cr…
Both D0 and CDF at Tevatron reported the measurements of forward-backward asymmetry in top pair production, which showed possible deviation from the standard model QCD prediction. In this paper, we explore how to examine the {\em same} higher-order QCD effects at the more powerful Large Hadron Collider.
The large forward-backward asymmetry of the top quark pair production measured by the hadron colliders shed light on new physics signals beyond the Standard Model. In the Randall-Sundrum model with an additional SU(3) group in the strong sector, we compare the total cross section and forward-backward asymmetry of the top quark pair production with the newest data obtained by the CDF and the D0 collaborations. Our numerical analysis shows that the parameter $c_q \gtrsim 0.5$, $c_t \sim -0.6\sim-0.8$, $\tanϕ\gtrsim 20$ or $\tanϕ\leq 1/20$ and the first excitation of axial gluon with a mass about…
The updated CDF measurement of the forward-backward asymmetry (FBA) in the top quark production p{bar p} -> t{bar t} at Tevatron (with the CMS energy 1.96 TeV) shows a deviation of 2*sigma from the value predicted by the Standard QCD Model. We present calculation of this quantity in the scenario where colored unparticle physics contributes to the s-channel of the process, and obtain the regions in the plane of the unparticle parameters lambda and dU which give the values of the FBA and of the total t{bar t} production cross section compatible with the present measurements.
We show that the scalar sector needed for fermion mass generation when the flavor symmetry of the standard model is maximally gauged can consistently explain two anomalies reported recently by the CDF collaboration - the forward-backward asymmetry in t-tbar pair production, and the dijet invariant mass in the Wjj channel. A pair of nearly degenerate scalar doublets with masses in the range 150-200 GeV explain these anomalies, with additional scalars predicted in the mass range 100-400 GeV. Consistency of such low scale flavor physics with flavor changing processes is shown, and expectations fo…
We examine the implications of the recent CDF measurement of the top-quark forward-backward asymmetry, focusing on a scenario with a new color octet vector boson at 1-3 TeV. We study several models, as well as a general effective field theory, and determine the parameter space which provides the best simultaneous fit to the CDF asymmetry, the Tevatron top pair production cross section, and the exclusion regions from LHC dijet resonance and contact interaction searches. Flavor constraints on these models are more subtle and less severe than the literature indicates. We find a large region of al…
We show that the anomalously large top quark forward-backward asymmetry observed by CDF and DØ\, can naturally be accommodated in models with flavor-violating couplings of a new massive spin-2 state to quarks. Regardless of its origin, the lowest-order couplings of a spin-2 boson to fermions are analogous to the coupling of the graviton to energy/momentum, leading to strong sensitivity of the effects associated with its virtual exchange to the energy scales at hand. Precisely due to this fact, the observed dependence of the asymmetry on the $t\bar t$ invariant mass fits nicely into the propose…
In this paper we re-examine how to utilize the previous proposed color-octet axial-vector boson $Z_{\rm C}$ to explain the $3.4σ$ anomaly of $t\bar t$ forward-backward (FB) asymmetry $A_{\rm FB}$ for $m_{t\bar t}> 450$GeV observed by CDF. Our numerical results indicate that the best-fit parameters are $g_A^q=0.07$, $g_A^Q=3$, and $M_{\rm C}=440\text{GeV}$, which are obtained by fitting the mass dependent $A_{\rm FB}$ and total cross section data provided by a recent CDF measurement. Here $g_A^q (g_A^Q)$ and $M_{\rm C}$ are the axial couplings among $Z_{\rm C}$ with the first two (the third) ge…
The CDF and D0 experiments have reported on the measurement of the forward-backward asymmetry of top quark pair production at the Tevatron and the result is that it is more than 2 standard deviations above the predicted value in the Standard Model. This has to be added to the longstanding anomaly in the forward-backward asymmetry for bottom quark production at LEP which is 3 standard deviations different from the Standard Model value. The discrepancy in the bottom asymmetry can be accounted for by the contributions of Kaluza-Klein excitations of electroweak gauge bosons at LEP in warped extra …
Motivated by the recent unexpected large forward-backward asymmetry (FBA) of the top quark observed by D$Ø$ and CDF at the Tevatron, we investigate a possible explanation for the anomaly within the framework of diquark models. Unlike other mechanisms induced by s-channel or t-channel, the top-quark pair production in the diquark models is dictated by the u-channel diagram. We find that the color-triplet diquark can generate the FBA of 20% when the constraint from the cross section of the top-quark pair production is taken into account.
The LEP experiment at CERN provided accurate measurements of the $Z$ neutral gauge boson properties. Although all measurements agree well with the SM predictions, the forward backward asymmetry of the bottom-quark remains almost 3$σ$ away from the SM value. We proposed that this anomaly may be explained by the existence of a new $U(1)_D$ gauge boson, which couples with opposite charges to the right-handed components of the bottom and charm quarks. Cancellation of gauge anomalies demands the presence of a vector-like singlet charged lepton as well as a neutral Dirac (or Majorana) particle that …
The renormalization scale uncertainty can be eliminated by the Principle of Maximum Conformality (PMC) in a systematic scheme-independent way. Applying the PMC for the $t\bar{t}$-pair hadroproduction at the NNLO level, we have found that the total cross-sections $σ_{t\bar{t}}$ at both the Tevatron and LHC remain almost unchanged when taking very disparate initial scales $μ^{\rm init}_R$ equal to $m_t$, $10\,m_t$, $20\,m_t$ and $\sqrt{s}$, which is consistent with renormalization group invariance. As an important new application, we apply PMC scale-setting to study the top-quark forward-backwar…
We adopt a Markov Chain Monte Carlo method to examine various new physics models which can generate the forward-backward asymmetry in top quark pair production observed at the Tevatron by the CDF Collaboration. We study the following new physics models: (1) exotic gluon $G^\prime$, (2) extra $Z^\prime$ boson with flavor-conserving interaction, (3) extra $Z^\prime$ with flavor-violating $u$-$t$-$Z^\prime$ interaction, (4) extra $W^\prime$ with flavor-violating $d$-$t$-$W^\prime$ interaction, and (5) extra scalars $S$ and $S^\pm$ with flavor-violating $u$-$t$-$S$ and $d$-$t$-$S^\pm$ interactions…
The CDF and D0 collaborations have recently reported a large forward-backward asymmetry in the ttbar system which deviates from the next to-leading order QCD standard model prediction. We study the asymmetry in the ttbar system within the framework of singlet extensions of the Minimal Supersymmetric Standard Model. For this purpose, we introduce non-renormalizable couplings between first and third generation of quarks to scalars. We analyze two limiting cases of the model, characterized by the size of the supersymmetric mass for the singlet superfield. We study both the small and large limits …
We examine loop-mediated effects of new heavy quarks Q=(t',b') on t tbar production at hadron colliders, using a phenomenological model with flavor off-diagonal couplings of charged and neutral scalars phi=(phi^+-,phi^0) to Q. We show that an invariant-mass-dependent asymmetry, in the t tbar center of mass, consistent with those recently reported by the CDF collaboration can be obtained for quark masses around 350-500 GeV, scalar masses of order 100-200 GeV, and modest to strong Yukawa couplings. The requisite strong interactions suggest a non-perturbative electroweak symmetry breaking mechani…
We suggest that top physics can be studied at the LHCb experiment, and that top production could be observed. Since LHCb covers a large pseudorapidity region in the forward direction, it has unique abilities to probe new physics in the top sector. Furthermore, we demonstrate that LHCb may be able to measure a t\bar t production rate asymmetry, and thus indirectly probe an anomalous forward backward t\bar t asymmetry in the forward region; a possibility suggested by the enhanced forward-backward asymmetry reported by the CDF experiment.
The forward-backward asymmetry A_{FB}^t in top quark production at the Tevatron has been seen to be anomalously large both by CDF and D0. Parton-level asymmetries as large as 50%, with a large error bar, have been extracted from the data. It is important to measure other quark asymmetries if possible, as these would help clarify the source of any new physics behind A_{FB}^t. In this note it is argued that asymmetries in b\bar b and c\bar c should be accessible to the Tevatron experiments, using the full data sets. A crude study suggests that muon asymmetries in high-p_T dijet events, with suit…
Motivated by the first measurement on $\mathcal{B}(B_s\toϕμ^+μ^-)$ by the CDF Collaboration, we study the supersymmetric effects in semi-leptonic $B_s\toϕμ^+μ^-$ decay. In our evaluations, we analyze the dependences of the dimuon invariant mass spectrum and the forward-backward asymmetry on relevant supersymmetric couplings in the MSSM with and without R-parity. The analyses show the new experimental upper limits of $\mathcal{B}(B_s\toμ^+μ^-)$ from the LHCb Collaboration could further improve the bounds on sneutrino exchange couplings and $(δ^u_{LL})_{23}$ as well as $(δ^d_{LL,RR})_{23}$ mass …
Both CDF and D0 at Tevatron reported the measurements of forward-backward asymmetry in top pair production, which showed possible deviation from the standard model QCD prediction. In this paper, we show that a new color-octet massive vector boson with mass just above twice that of top quark can simultaneously account for the asymmetry and differential distribution $dσ/dM_{t\bar t}$ in top pair production, without conflict with other measurements for example di-jet production. The new particle can be discovered and studied at the more powerful Large Hadron Collider.
CDF recently reported an anomaly in the $m_{jj}$ distribution of dijet events produced in association with a $W$ boson. If this anomaly is associated with a new flavor conserving vector resonance, $V$, one might have expected to observe effects in the analogous $m_{jj}$ distribution produced in association with a $γ$. No such excess is observed. A single $u-t-V$ flavor changing coupling, however, can contribute to the $m_{jj}$ anomaly while being consistent with other resonance searches. Furthermore, it gives a potential explanation of the observed forward-backward asymmetry in top quark produ…
We analyze various models for the top quark forward-backward asymmetry ($A^t_{FB}$) at the Tevatron, using the latest CDF measurements on different $A^t_{FB}$s and the total cross section. The axigluon model in Ref. \cite{paul} has difficulties in explaining the large rapidity dependent asymmetry and mass dependent asymmetry simultaneously and the parameter space relevant to $A^t_{FB}$ is ruled out by the latest dijet search at ATLAS. In contrast to Ref. \cite{cp}, we demonstrate that the large parameter space in this model with a $U(1)_d$ flavor symemtry is not ruled out by flavor physics. Th…
Both CDF and DO report a forward-backward asymmetry in t-tbar production that is above the standard model prediction. We review new physics models that can give a large forward backward asymmetry in t-tbar production at the Tevatron and the constraints these models face from searches for dijet resonances and contact interactions, from flavor physics and the t-tbar cross section. Expected signals at the LHC are also reviewed.
The forward-backward asymmetry (FBA) in top-pair production that was observed in 2008 gets a boost in a recent CDF publication. Not only has the FBA further been confirmed, but also distributional preferences are shown. Strikingly, the FBA is the most sizable in the large $M_{t\bar t}$ invariant mass region and in the large rapidity difference $|Δy|$ region. Here we used our previously proposed $t$-channel exchanged $W'$ boson to explain the new observations. We show that a new particle exchanged in the $t$-channel generically gives rise to such observations. Furthermore, we show that the prop…
The measurement of forward-backward asymmetry in the top and anti-top quark ($t \bar{t}$) production has been recently reconfirmed by the CDF Collaboration and shows a more than $3σ$ deviation from the Standard Model(SM) prediction in the large $t \bar{t}$ invariant mass region. Models with new W$^{\prime}$ or Z$^{\prime}$ bosons have been invoked to explain this deviation. In the context of these models we perform a $χ^2$ analysis with all the available experimental numbers in different $ΔY$ and $M_{t \bar{t}}$ bins. We show that for the $Z^{\prime}$ model the region of parameter space which …
The forward-backward asymmetry in top pair production at Tevatron has been reconfirmed by the CDF collaboration with 5.3 fb^{-1} of accumulated data. These measurements also report that the asymmetry is the largest in regions of high invariant mass M_{t\bar{t}} and rapidity difference |ΔY|. We consider light colored sextet scalars appearing in a particular non-supersymmetric \10 grand unification model within the \bar{126} scalar representation. These scalar states have masses in the range of 300 \text{GeV}-2 \text{TeV} consistent with the requirements of gauge coupling unification and bounds …
CDF has observed a top forward-backward asymmetry discrepant with the Standard Model prediction at 3.4 σ. We analyze models that could generate the asymmetry, including flavor-violating W's, horizontal Z'_Hs, triplet and sextet diquarks, and axigluons. We consider the detailed predictions of these models for the invariant mass and rapidity distributions of the asymmetry at the parton level, comparing against the unfolded parton-level CDF results. While all models can reproduce the asymmetry with the appropriate choice of mass and couplings, it appears at first examination that the extracted pa…
We present a phenomenological analysis of the recent Tevatron results on the $t \bar t$ forward-backward asymmetry and invariant-mass spectrum assuming a new contribution from an s-channel gluon resonance with a mass in the range from 700 to 2500 GeV. In contrast to most of the previous works, this analysis shows that for masses below ~1 TeV resonant New Physics could accommodate the experimental data. In general, we find that axial-like couplings are preferred for light and top quark couplings, and that only top quark couples strongly to New Physics. We find that composite model scenarios ari…
Among different measured observables of top-antitop quark pairs at hadron colliders, the forward-backward asymmetry ($A_{\text{FB}}$) measured by the CDF and D0 collaborations has inconsistency with the Standard Model prediction. The measured forward-backward asymmetry grows with $t\bar{t}$ invariant mass. Several new physics models have been proposed to explain this deviation. We consider the consistency of the parameter space of vector unparticle (in Flavor-Conserving scenario) with the existing $t\bar{t}$ production measurements. In particular, we look at the total cross sections at the LHC…
The top quark has been discovered in 1995 by the CDF and D0 experiments located at the two beam-crossing points at the Tevatron ppbar collider. The top quark is the most massive of the known elementary particles. At hadron-hadron colliders, top quarks are mostly produced in pairs through strong interactions. The measurement of the cross section for top quark pair production is a test of our understanding of QCD prediction at next-to-leading order (NLO). This measurement requires a deep understanding of the backgrounds to top quark production, thus setting the ground for the measurements of top…
We discuss the phenomenology of effective field theories with new scalar or vector representations of the Standard Model quark flavor symmetry group, allowing for large flavor breaking involving the third generation. Such field content can have a relatively low mass scale \lesssim TeV and O(1) couplings to quarks, while being naturally consistent with both flavor violating and flavor diagonal constraints. These theories therefore have the potential for early discovery at LHC, and provide a flavor safe "tool box" for addressing anomalies at colliders and low energy experiments. We catalogue the…
We explore the possibility that the large $t\bar t$ forward-backward asymmetry measured by the CDF detector at Tevatron could be due to a universal effective axial-vector coupling of gluon. Using an effective field theory approach we show model independently how such a log-enhanced coupling occurs at 1-loop level. The interference with QCD gluon vector coupling naturally induces the observed positive forward-backward $t\bar t$ asymmetry that grows with $t\bar t$ invariant mass and is consistent with the cross section measurements. This scenario does not involve new flavor changing couplings no…
We study the top forward-backward asymmetry (FBA $\equiv A_{\rm FB}$) reported by CDF and D0 Collaborations in the effective lagrangian approach. Using dimension-6 effective largrangians for $q \bar{q} \rightarrow t \bar{t}$, we study the $t\bar{t}$ production cross section and the $A_{\rm FB}$, and a few observables: the FB spin-spin correlation that is strongly correlated with the $A_{\rm FB}$, and longitudinal top polarization as a new probe of chiral structures for possible new physics scenarios.
We carry out a comprehensive analysis of models for top A_{FB} at CDF in light of new top data arriving from the LHC. We begin with a careful Tevatron analysis, considering in general which sets of effective vertices give rise to a large forward-backward asymmetry while suppressing the contribution to the total t tbar cross-section. We show on general grounds that scalar models struggle to produce sufficient asymmetries consistent with CDF observations, while vector models can produce a large asymmetry with a less significant tension in the total cross-section and $t\bar{t}$ invariant mass dis…
We propose a supersymmetric explanation for the anomalously high forward backward asymmetry in top pair production measured by CDF and D0. We suppose that it is due to the t-channel exchange of a right-handed sbottom which couples to d_R and t_R, as is present in the R-parity violating minimal supersymmetric standard model. We show that all Tevatron and LHC experiments' t tbar constraints may be respected for a sbottom mass between 300 and 1200 GeV, and a large Yukawa coupling >2.2, yielding A_{FB} up to 0.18. The non Standard Model contribution to the LHC charge asymmetry parameter is Delta A…
We show that very light (50 - 90 GeV) axigluons with flavor-universal couplings of order g_{s}/3 may explain the anomalous top forward-backward asymmetry reported by both CDF and D0 collaborations. The model is naturally consistent with the observed t \bar t invariant mass distribution and evades bounds from light Higgs searches, LEP event shapes, and hadronic observables at the Z pole. Very light axigluons can appear as resonances in multijet events, but searches require sensitivity to masses below current limits.
The contributions of $G'$-boson predicted by the chiral color symmetry of quarks to the charge asymmetry $A_C(p p \to t\bar{t})$ in $t \bar{t}$ production at the LHC and to the forward-backward asymmetry $A_{\rm FB}(p\bar{p} \to t\bar{t})$ in $t\bar{t}$ production at the Tevatron are calculated and analysed in dependence on two free parameters of the model, the $G'$ mass $m_{G'}$ and mixing angle $θ_G$. The $m_{G'} - θ_G$ regions of $1 σ$ consistency with the CMS data on the cross section $σ(pp \to t\bar{t})$ and on the charge asymmetry $A_C(p p \to t\bar{t})$ are found and compared with those…
We use a recent upper limit from CDF on like-sign top pair production to place constraints on general new vector bosons and scalars mediating u u -> t t. The possible vector bosons comprise neutral colour singlets or octets, and charge 4/3 colour triplets or sextets, whereas the new scalars can be neutral colour singlets or octets and charge 4/3 colour sextets. We also estimate the expected bounds from like-sign top pair production at LHC in the near future. Then, we address the implications of these limits for the forward-backward asymmetry in t tbar production measured at Tevatron. In partic…
Recent experimental results from the CDF collaboration which study the top forward-backward asymmetry have strengthened the case that new physics is playing a role in t-tbar production. Here we propose a set of measurements, built from the charged lepton kinematics in semileptonic and fully leptonic t-tbar events, designed to further probe the underlying causes of this asymmetry both at the Tevatron and at the LHC. Using a set of conservative reference models we find that measurements of the charged lepton asymmetry, top polarization, and t-tbar spin correlation can establish the existence of …
Recent results from the CDF Collaboration indicate the the top-pair forward-backward asymmetry is largest in regions of high rapidity difference $|Δy|$ and invariant mass $M_{t\bar t}.$ We show that experimental observations can be explained by our previously proposed Asymmetric Left-Right Model (ALRM). The gauge symmetry $U'(1)\times SU'(2)\times SU(2)$ is broken by a triplet Higgs in the primed sector. The $W'$ boson has a $(t,d)$ right-handed coupling and the $Z'$ boson has diagonal fermion couplings. We determine the model parameters to be $M_{W'} = 700$ GeV, $M_{Z'}=1$ TeV, and charged cu…
The fully differential angular distribution for the rare flavor-changing neutral current decay {\bar B}_d^0 -> {\bar K}^{*0} (-> K^- π^+) e+ e- is studied. The emphasis is placed on accurate treatment of the contribution from the processes \bar{B}_d^0 -> \bar{K}^{*0} (-> K^- pi^+) V with intermediate vector resonances V = ρ(770), ω(782), ϕ(1020), J/ψ, ψ(2S), ... decaying into the e+ e- pair. The two versions of the vector-meson-dominance model for the transition V γare used and tested. The present method of including vector resonances is also compared with the existing in the literature method…
New colour octets stand out among the new physics proposals to explain the anomalous forward-backward asymmetry measured in $t \bar t$ production by the CDF experiment at the Tevatron. We perform a fit to $t \bar t$ observables at the Tevatron and the LHC, including total cross sections, various asymmetries and the top polarisation and spin correlations, to find the most likely parameters of a light colour octet to be consistent with data. In particular, an octet coupling only to right-handed quarks gives a good fit to all measurements. The implications from the general fit are drawn in terms …
The recent Tevatron measurement of the forward-backward asymmetry of the top quark shows an intriguing discrepancy with Standard Model expectations, particularly at large $\ttbar$ invariant masses. Measurements of this quantity are subtle at the LHC, due to its $pp$ initial state, however, one can define a forward-central-charge asymmetry which captures the physics. We study the capability of the LHC to measure this asymmetry and find that within the SM a measurement at the $5σ$ level is possible with roughly 60 fb$^{-1}$ at $\sqrt{s} = 14$ TeV. If nature realizes a model which enhances the as…
In this paper, we compute the forward-backward asymmetry and the isospin asymmetry of the $B \to K^* μ^+ μ^-$ decay. The $B \to K^*$ transition form factors (TFFs) are key components of the decay. To achieve a more accurate QCD prediction, we adopt a chiral correlator for calculating the QCD light-cone sum rules for those TFFs with the purpose of suppressing the uncertain high-twist distribution amplitudes. Our predictions show that the asymmetries under the Standard Model and the Minimal Supersymmetric Standard Model with minimal flavor violation are close in shape for $q^2 \ge 6~{\rm GeV}^2$…
We present U(1) flavor models for leptophobic Z' with flavor dependent couplings to the right-handed up-type quarks in the Standard Model, which can accommodate the recent data on the top forward-backward (FB) asymmetry and the dijet resonance associated with a W boson reported by CDF Collaboration. Such flavor-dependent leptophobic charge assignments generally require extra chiral fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor symmetry calls for new U(1)'-charged Higgs doublets in order for the SM fermions to have realistic renormalizable Yukawa couplings. The strin…
With full data set that corresponds to an integrated luminosity of 9.4 fb$^{-1}$, CDF has updated the top quark forward-backward asymmetry (FBA) as functions of rapidity difference $|Δy|$ and $t\bar t$ invariant mass $M_{t\bar t}$. Beside the sustained inconsistency between experiments and standard model (SM) predictions at large $|Δy|$ and $M_{t\bar t}$, an unexpected large first Legendre moment with $a_1= 0.39\pm 0.108 $ is found. In order to solve the large top FBA, we study the contributions of color triplet scalar and color octet vector boson. We find that the top FBA at $|Δy| >1$ and $M_…
