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Top-Quark Forward-Backward Asymmetry in Randall-Sundrum Models Beyond the Leading Order
High Energy Physics - Phenomenology · Submitted 4 Aug 2010
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim In spite of this enhancement, the resulting RS corrections in A_FB^t remain marginal, leaving the predicted asymmetry SM-like.
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The abstract, sentence by sentence
We calculate the ttbar forward-backward asymmetry, A_FB^t, in Randall-Sundrum (RS) models taking into account the dominant next-to-leading order (NLO) corrections in QCD. At Born level we include the exchange of Kaluza-Klein (KK) gluons and photons, the Z boson and its KK excitations, as well as the Higgs boson, whereas beyond the leading order (LO) we consider the interference of tree-level KK-gluon exchange with one-loop QCD box diagrams and the corresponding bremsstrahlungs corrections. We find that the strong suppression of LO effects, that arises due to the elementary nature and the mostly vector-like couplings of light quarks, is lifted at NLO after paying the price of an additional factor of alpha_s/(4 pi). In spite of this enhancement, the resulting RS corrections in A_FB^t remain marginal, leaving the predicted asymmetry SM-like. As our arguments are solely based on the smallness of the axial-vector couplings of light quarks to the strong sector, our findings are model-independent and apply to many scenarios of new physics that address the flavor problem via geometrical sequestering.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We calculate the ttbar forward-backward asymmetry, A_FB^t, in Randall-Sundrum (RS) models taking into account the dominant next-to-leading order (NLO) corrections in QCD. | contribution 1.00 | 0.96 | 0.07 | asserted 0.97 |
| s1 | At Born level we include the exchange of Kaluza-Klein (KK) gluons and photons, the Z boson and its KK excitations, as well as the Higgs boson, whereas beyond the leading order (LO) we consider the interference of tree-level KK-gluon exchange with one-loop QCD box diagrams and the corresponding bremsstrahlungs corrections. | method 0.98 | 0.86 | 0.03 | asserted 0.98 |
| s2 | We find that the strong suppression of LO effects, that arises due to the elementary nature and the mostly vector-like couplings of light quarks, is lifted at NLO after paying the price of an additional factor of alpha_s/(4 pi). | result 0.91 | 0.95 | 0.12 | asserted 1.00 |
| s3 | In spite of this enhancement, the resulting RS corrections in A_FB^t remain marginal, leaving the predicted asymmetry SM-like. | result 0.91 | 0.92 | 0.83 | asserted 1.00 |
| s4 | As our arguments are solely based on the smallness of the axial-vector couplings of light quarks to the strong sector, our findings are model-independent and apply to many scenarios of new physics that address the flavor problem via geometrical sequestering. | interpretation 1.00 | 0.67 | 0.12 | asserted 1.00 |
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The paper
Original abstract
We calculate the ttbar forward-backward asymmetry, A_FB^t, in Randall-Sundrum (RS) models taking into account the dominant next-to-leading order (NLO) corrections in QCD. At Born level we include the exchange of Kaluza-Klein (KK) gluons and photons, the Z boson and its KK excitations, as well as the Higgs boson, whereas beyond the leading order (LO) we consider the interference of tree-level KK-gluon exchange with one-loop QCD box diagrams and the corresponding bremsstrahlungs corrections. We find that the strong suppression of LO effects, that arises due to the elementary nature and the mostly vector-like couplings of light quarks, is lifted at NLO after paying the price of an additional factor of alpha_s/(4 pi). In spite of this enhancement, the resulting RS corrections in A_FB^t remain marginal, leaving the predicted asymmetry SM-like. As our arguments are solely based on the smallness of the axial-vector couplings of light quarks to the strong sector, our findings are model-independent and apply to many scenarios of new physics that address the flavor problem via geometrical sequestering.
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References
How the literature uses it
36 arXiv papers cite this in 45 sentences
Papers citing it · 26 sentences without a confident label
Uses its method or tool 1 paper
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Using Eqs. ([ref]), ([ref]), and ([ref]), and focussing on the dominant contributions from $uu̅$ initial states, one obtains [For details on the inputs and the numerical calculation, please consult [ref] .] [equation] Discarding the axial-vector contributions, proportional to $C̃_uu̅^A = 𝒪(10^-3)$, we inspect the interplay of NP effects mediated by the vector coefficient $C̃_uu̅^V$.
Top-Quark Forward-Backward Symmetry · Discussion and conclusions · 0.90
Compares with it 1 paper
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Therefore, although there is a clear improvement in the top $A_FB$ prediction compared with Ref. [ref] , and there is also an improvement in the EW precision observables compared with the scenario without custodial protection, those analysis have to be done to ensure the viability of this model.
A composite Higgs model analysis of forward-backward asymmetries in the production of tops at Tevatron and bottoms at LEP and SLC · Discussions · 0.82
Cites it as background 15 papers
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In the wake of this $3.4σ$ deviation of the observed value of the top quark FBA from the SM predicted one, several possible solutions have been proposed and studied by authors in Refs. [ref] .
Rare B decays and Tevatron top-pair asymmetry · Introduction · 0.90
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Another kind of widely discussed NP is the s-channel color-octet axial-vector boson [ref] , where the new boson induces a new s-channel $qq̅→tt̅$.
New color-octet axial vector boson revisited · Introduction · 0.98
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However, from a phenomenological point of view, these models mainly fall into only two categories according to the nature of the new particle exchange: (i) $s$-channel exchange of vector mediators (e.g. axigluon models) [ref] or (ii) $t$-channel exchange of flavor-violating mediators [ref] [There is another class of models that can create effective axial QCD coupling from NP [ref] . ].
Tevatron Top $A_{FB}$ Versus LHC Top Physics · Introduction · 0.85
What it cites · 64 sentences without a confident label
Uses the method or tool of 5 papers
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The bulk mass parameters have then been determined using the warped-space Froggatt-Nielsen formulas given in [ref] , which guarantees that the quark masses and mixings are correctly reproduced.
Flavor Physics in the Randall-Sundrum Model: I. Theoretical Setup and Electroweak Precision Tests · Parameter Points · 0.99
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The central value of our SM prediction has been obtained by integrating the formulas given in [ref] over the relevant phase space (see ([ref]) to ([ref])), weighted with MSTW2008LO PDFs with the unphysical scales fixed to $m_t$.
Charge asymmetry of heavy quarks at hadron colliders · Numerical Analysis · 0.86
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For further details concerning the algorithm used to scan the parameter space of the RS model, the interested reader is referred to [ref] .
Flavor Physics in the Randall-Sundrum Model: II. Tree-Level Weak-Interaction Processes · Parameter Points · 0.91
Uses data or values from 3 papers
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The latest result for $$ has already been given in ([ref]) and the most recent Tevatron results ($√(s) = 1.96 TeV$) for the remaining measurements of interest read [ref] [equation] Here the quoted individual errors are of statistical and systematic origin, and due to the luminosity uncertainty, respectively.
First Measurement of the $\lowercase{\ttbar}$ Differential Cross Section $\lowercase{d\sigma/d}M_{\lowercase{{t\overline{t}}}}$ in $\lowercase{\ppbar}$ Collisions at $\sqrt{\lowercase{s}}=1.96$ TeV · Numerical Analysis · 1.00
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For typical values of the bulk mass parameters, $c_t_L = -0.34$, $c_t_R = 0.57$, $c_u_L = -0.63$, and $c_u_R = -0.68$ [ref] , one finds numerically that the first term in the curly bracket of eq:SALOscaling2, which is enhanced by a factor of $L$ but suppressed by the small difference $(c_u_L - c_u_R)$ of bulk mass parameters, is larger in magnitude than the second one by almost a factor of 10.
Flavor Physics in the Randall-Sundrum Model: II. Tree-Level Weak-Interaction Processes · Calculation of LO Effects · 0.89
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Up to now, the CDF and DØ experiments at the Tevatron have collected thousands of top-quark pair events, which allowed them to measure the top-quark mass, $m_t$, and its total inclusive cross section, $$, with an accuracy of below $1%$ [ref] and $10%$ [ref] , respectively.
Combination of CDF and D0 Results on the Mass of the Top Quark · Introduction · 0.88
Compares with 7 papers
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Our results should be contrasted with the analysis [ref] , which finds positive corrections to the $t t̅$ forward-backward asymmetry of up to $5.6%$ ($7%$) arising from KK gluons ($Z^'$-boson exchange) at LO.
The forward-backward asymmetry of top quark production at the Tevatron in warped extra dimensional models · Numerical Analysis · 0.97
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It is in good agreement with ([ref]) as well as the findings of [ref] .
Threshold Resummation for the Top Quark Charge Asymmetry · Numerical Analysis · 0.98
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It is in good agreement with ([ref]) as well as the findings of [ref] .
Renormalization-Group Improved Predictions for Top-Quark Pair Production at Hadron Colliders · Numerical Analysis · 0.98
Cites as support 1 paper
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Taken together, it turns out that the discussed features of $A_uu̅, RS^(0)$ render the tree-level contribution to the charge asymmetry in the RS framework tiny.[This conclusion can also be drawn from the statements made in [ref] concerning the mostly vector-like couplings of light quarks.] As we will see below in our numerical analysis, the inclusion of electroweak corrections arising from the Born-level exchange of the $Z$ boson, of KK excitations of both the photon and the $Z$ boson as well as of the Higgs boson, do not change this picture qualitatively.
LHC Signals from Warped Extra Dimensions · Calculation of LO Effects · 0.98
Cites as background 24 papers
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If the SM fermions and gauge bosons are allowed to propagate in the bulk of the extra dimension [ref] , the RS model is in addition a promising theory of flavor [ref] .[A list of further relevant references can be found in [ref] .] Since the fermion zero modes are exponentially localized either in the UV (light SM fermions) or IR (heavy SM fermions), the effective Yukawa couplings resulting from their wave-function overlap with the Higgs boson naturally exhibit exponential hierarchies.
Flavor Physics in the Randall-Sundrum Model: II. Tree-Level Weak-Interaction Processes · Cross Section and Asymmetry in RS Models · 0.90
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If the SM fermions and gauge bosons are allowed to propagate in the bulk of the extra dimension [ref] , the RS model is in addition a promising theory of flavor [ref] .[A list of further relevant references can be found in [ref] .] Since the fermion zero modes are exponentially localized either in the UV (light SM fermions) or IR (heavy SM fermions), the effective Yukawa couplings resulting from their wave-function overlap with the Higgs boson naturally exhibit exponential hierarchies.
Flavor Structure of Warped Extra Dimension Models · Cross Section and Asymmetry in RS Models · 0.90
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If the SM fermions and gauge bosons are allowed to propagate in the bulk of the extra dimension [ref] , the RS model is in addition a promising theory of flavor [ref] .[A list of further relevant references can be found in [ref] .] Since the fermion zero modes are exponentially localized either in the UV (light SM fermions) or IR (heavy SM fermions), the effective Yukawa couplings resulting from their wave-function overlap with the Higgs boson naturally exhibit exponential hierarchies.
Gauge bosons in a five-dimensional theory with localized gravity · Cross Section and Asymmetry in RS Models · 0.90
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