arXiv subjects

Shaouly Bar-Shalom

Publications and source records attributed to Shaouly Bar-Shalom.

At least 19 recordsLinked to original sources

arXiv2026

Counting b-jets at the FCC-ee as a probe of top-quark flavor physics

We explore the sensitivity of a future FCC-ee to multi-TeV new physics (NP) that can generate vector, scalar and tensor flavor-changing (FC) $eetu_k$ contact interactions ($u_k=u,c$ for $k=1,2$), probed via single top-quark production, $e^+ e^- \to t \bar{u}_k, t \bar{u}_k γ$ (+ c.c.) and leading (following the top-quark decay) to two- and four-jet signals, $e^+ e^- \to 2j + X, 4j + X$, where $X$ denotes any non-jet final-state particles. Our analysis exploits an approximately conserved Standard Model (SM) quantum number introduced in [1] and termed "$b$-Parity" ($b_P$), which is applicable to scattering processes of the type $e^+ e^- \to n \cdot j_b + m \cdot j_\ell + X$, where $n$ and $m$ are the number of produced $b$-jets and light-jets ($u,d,c,s,$ and/or gluons) and $b_P=(-1)^n$. The FC $eetu_k$ four-fermion interactions can generate distinct $b_P$-odd ($b_P = -1$) signals in these multi-jet events, for which the only significant SM background stems from $b$-jet misidentification. We demonstrate that the FCC-ee, operating at a $\sqrt{s} = 240$ GeV (the $ZH$ run phase) with high luminosity and excellent flavor-tagging performance, is an ideal platform to search for these $b_P$-odd signatures. Indeed, by simply counting the number of final-state $b$-jets, the FCC-ee can probe NP scales of $Λ\sim 10$ TeV for the new heavy states that generate the vector, scalar and tensor $eetu$ and/or $eetc$ interactions. This reach, remarkably about 40 times the assumed FCC-ee center-of-mass energy, improves upon current bounds on some of these four-fermion operators by an order of magnitude and it critically relies on high-purity b-jet tagging.

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arXiv2026

Flavor physics at the EIC with b-jet tagging

We employ an approximate conserved quantum number (defined as "$b$-Parity" in [1]) of the Standard Model (SM): $b_P=(-1)^n$, where $n$ is the number of produced $b$-jets in the reaction $e + p/A \to n \cdot j_b +X$, to explore new TeV-scale flavor-changing interactions involving the 3rd generation quarks at the EIC; simply by counting the number of $b$-jets in the final state. In particular, the SM single and di-jet production at the EIC which occur through charge current interactions, $e + p/A \to j + \!\not\!E_T$ and $e + p/A \to 2\cdot j + \!\not\!E_T$, are $b_P$-even since the $b_P$-violating (i.e, $b_P=-1$) SM signals for these processes are necessarily CKM suppressed and, therefore, have a vanishingly small production rate. In contrast, new flavor physics can generate $b_P=-1$ signals at the EIC whose only significant SM background is due to $b$-jet misidentification. We thus show that $b_P$ can be used as a simple and sensitive probe of new flavor violating physics; specifically, we find that counting single $b$-jet events in $e + p/A \to j + \!\not\!E_T$ at the EIC with a center-of-mass (CM) energy of $\sqrt{s} \sim 140$ GeV, can probe scales of new physics up to $Λ\sim {\cal O}(5)$ TeV for a certain type of new chiral flavor-changing physics in 3rd generation interactions. This is remarkably more than 30 times larger than the assumed EIC CM energy and it critically depends on the $b$-tagging efficiency and purity as well as the feasibility of electron-beam polarization. The sensitivity of the di-jet process, $e + p/A \to 2j + \!\not\!E_T$, to these type of new physics is reduced compared to the single-jet channel.

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arXiv2024

Theoretical underpinnings of CP-Violation at the High-energy Frontier

We present a general analysis for the discovery potential of CP-violation (CPV) searches in scattering processes at TeV-scale colliders in an effective field theory framework, using the SMEFT basis for higher dimensional operators. In particular, we systematically examine the CP-violating sector of the SMEFT framework in some well motivated limiting cases, based on flavour symmetries of the underlying heavy theory. We show that, under naturality arguments of the underlying new physics (NP) and in the absence of (or suppressed) flavour-changing interactions, there is only a single operator, $Q_{tϕ} = ϕ^\dagger ϕ\left(\bar q_3 t \right) \tildeϕ $ which alters the top-Yukawa coupling, that can generate a non-vanishing CP-violating effect from tree-level SM$\times$NP interference terms. We find, however, that CPV from $Q_{tϕ} = ϕ^\dagger ϕ\left(\bar q_3 t \right) \tildeϕ $ is expected to be at best of $O(1\%)$ and, therefore, very challenging if at all measurable at the LHC or other future high-energy colliders. We then conclude that a potentially measurable CP-violating effect of $O(10\%)$ can arise in high-energy scattering processes ONLY if flavour-changing interactions are present in the underlying NP; in this case a sizable CPV can be generated at the tree-level by pure NP$\times$NP effects and not from SM$\times$NP interference. We provide several examples of CPV at the LHC and at a future $e^+e^-$ collider to support these statements.

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arXiv2023

Generic tests of CP-violation in high-$p_\text{T}$ multi-lepton signals at the LHC and beyond

We introduce a modification to the standard expression for tree-level CP-violation in scattering processes at the LHC, which is important when the initial state in not self-conjugate. Based on that, we propose a generic and model-independent search strategy for probing tree-level CP-violation in inclusive multi-lepton signals. We then use TeV-scale 4-fermion operators of the form $tu\ell\ell$ and $tc \ell \ell$ with complex Wilson coefficients as an illustrative example and show that it may generate ${\cal O}(10\%)$ CP asymmetries that should be accessible at the LHC with an integrated luminosity of ${\cal O}(1000)$ fb$^{-1}$.

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arXiv2023

CP tests for high-$p_T$ multi-leptons

We propose a generic and model-independent search strategy for probing tree-level CP-violation in inclusive multi-lepton signals and we extend the standard expression for tree-level CP-violation in scattering processes at the LHC to include the cases where the initial state in not self-conjugate. We then use TeV-scale 4-fermion operators of the form $tu\ell\ell$ and $tc \ell \ell$ with complex Wilson coefficients as an illustrative example and show that it may generate ${\cal O}(10\%)$ CP asymmetries that should be accessible at the LHC with an integrated luminosity of ${\cal O}(1000)$ fb$^{-1}$

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arXiv2022

Multi-lepton probes of new physics and lepton-universality in top-quark interactions

We explore the sensitivity to new physics (NP) in the associated production of top-quarks with leptons $pp \to t \bar t \ell^+ \ell^-$, which leads to the multi-leptons signals $pp \to n \ell + {\tt jets} + \not\!\! E_T$, where $n = 2,3,4$. The NP is parameterized via 4-Fermi effective $t\bar{t} \ell^+ \ell^-$ contact interactions of various types, which are generated by multi-TeV heavy scalar, vector or tensor exchanges in $t \bar t \to \ell^+ \ell^-$; we focus on the case of $\ell=e,μ$. We match the 4-Fermi $t t \ell \ell$ terms to the SMEFT operators and also give examples of specific underlying heavy physics that can generate such terms. Analysis of the SM signals and corresponding backgrounds shows that the di-lepton and tri-lepton channels are much better probes of the effective $t\bar{t} \ell^+ \ell^-$ 4-Fermi terms than the four-lepton one at the 13 TeV LHC. Therefore, the best sensitivity is obtained in the di- and tri-lepton channels, for which the dominant background $pp \to t \bar t$ and $pp \to WZ$, respectively, can be essentially eliminated after applying the $2\ell$ and $ 3 \ell$ selections and a sufficiently high invariant mass selection for the opposite sign same flavor (OSSF) lepton-pair. We explore two cases: lepton flavor universal (LFU) NP where the $t t e e$ and $t t μμ$ contact interactions are of same size and LFU violating (LFUV) NP, where the scale of the $t t μμ$ terms is assumed to be much lower. We show that in both cases it is possible to obtain new 95\% CL bounds on the scale of the $t t \ell \ell$ contact interactions at the level $Λ\gtrsim 2-3$ TeV, which are considerably tighter than the current bounds on these 4-Fermi terms.

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arXiv2021

New flavor physics in di- and tri-lepton events from single-top at the LHC and beyond

The associated production of a single-top with opposite-sign same-flavor (OSSF) di-leptons, $pp \to t \ell^+ \ell^-$ and $ pp \to t \ell^+ \ell^- + j$ ($j=$light jet), can lead to striking tri-lepton $pp \to \ell^\prime \ell^+ \ell^- + X$ and di-lepton $pp \to \ell^+ \ell^- + j_b + X$ ($j_b=b$-jet) events at the LHC, after the top decays. Although these rather generic multi-lepton signals are flavor-blind, they can be generated by new 4-Fermi flavor changing (FC) $u_i t \ell \ell$ scalar, vector and tensor interactions ($u_i \in u,c$), which we study in this paper; we match the FC $u_i t \ell \ell$ 4-Fermi terms to the SMEFT operators and also to different types of FC underlying heavy physics. The main backgrounds to these di- and tri-lepton signals arise from $t \bar t$, $Z$+jets and $VV$ ($V=W,Z$) production, but they can be essentially eliminated with a sufficiently high invariant mass selection on the OSSF di-leptons, $m_{\ell^+ \ell^-}^{\tt min}(OSSF) > 1$ TeV; the use of $b$-tagging as an additional selection in the di-lepton final state case also proves very useful. We find, for example, that the expected 95\% CL bounds on the scale of a tensor(vector) $u t μμ$ interaction, with the current $\sim 140$ fb$^{-1}$ of LHC data, are $Λ< 5(3.2) $ TeV or $Λ< 4.1(2.7)$ TeV, if analyzed via the di-muon $μ^+ μ^- + j_b$ signal or the $e μ^+ μ^-$ tri-lepton one, respectively. The expected reach at the HL-LHC with 3000 fb$^{-1}$ of data is $Λ< 7.1(4.7)$ TeV and $Λ< 2.4(1.5)$ TeV for the corresponding $u t μμ$ and $c t μμ$ operators. We also study the potential sensitivity at future 27 TeV and 100 TeV high-energy LHC successors and also discuss the possible implications of this class of FC 4-Fermi effective interactions on lepton non-universality tests at the LHC.

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arXiv2020

High $p_T$ correlated tests of lepton universality in lepton(s) + jet(s) processes; an EFT analysis

We suggest a new class of tests for searching for lepton flavor non-universality (LFNU) using ratio observables and based on correlations among the underlying LFNU new physics (NP) effects in several (seemingly independent) di-lepton and single lepton + jet(s) processes. This is demonstrated by studying the effects generated by LFNU 4-Fermi interactions involving 3rd generation quarks. We find that the sensitivity to the scale ($Λ$) of the LFNU 4-Fermi operators significantly improves when the correlations among the various di-lepton +jets and single-lepton + jets processes are used, reaching $Λ\sim {\cal O}(10)$~TeV at the HL-LHC.

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arXiv2020

Searching for New Physics with $b\bar{b} \ell^+ \ell^-$ Contact Interactions

We study the impact of contact interactions involving two leptons (electrons or muons) and two $b$-quarks ($b \bar{b} \ell^+ \ell^-$) on the high-mass di-lepton region at the LHC. We consider different selections of $b$-tagged jet multiplicities in the di-lepton final states: inclusive (no selection), 0, 1 and 2 $b$-tagged jets, and show that the single $b$-jet selection significantly improves the sensitivity to New Physics (NP) in the form of the $b \bar{b} \ell^+ \ell^-$ contact term. We obtain a better sensitivity compared to the currently existing searches of NP in the di-lepton inclusive channel. In particular, the expected limits go beyond competitive bounds set by LEP (for electrons) on the scale of NP, $Λ$, by a factor of $1.2-3.1$, depending on the chirality structure of the operator. In addition, the expected limits on $Λ$, set by using a non-resonant LHC di-lepton inclusive search, are expected to be improved by a factor of $1.3-1.4$ for both electrons and muons.

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arXiv2019

Phenomenology of TeV-scale scalar Leptoquarks in the EFT

We examine new aspects of leptoquark (LQ) phenomenology using effective field theory (EFT). We construct a complete set of leading effective operators involving SU(2) singlets scalar LQ and the SM fields up to dimension six. We show that, while the renormalizable LQ-lepton-quark interaction Lagrangian can address the persistent hints for physics beyond the Standard Model in the B-decays $\bar B \to D^{(*)} τ\barν$, $\bar B \to \bar K \ell^+ \ell^-$ and in the measured anomalous magnetic moment of the muon, the LQ higher dimensional effective operators may lead to new interesting effects associated with lepton number violation. These include the generation of one-loop sub-eV Majorana neutrino masses, mediation of neutrinoless double-$β$ decay and novel LQ collider signals. For the latter, we focus on 3rd generation LQ ($ϕ_3$) in a framework with an approximate $Z_3$ generation symmetry, and show that one class of the dimension five LQ operators may give rise to a striking asymmetric same-charge $ϕ_3 ϕ_3$ pair-production signal, which leads to low background same-sign leptons signals at the LHC. For example, with $M_{ϕ_3} \sim 1$ TeV and a new physics scale of $Λ\sim 5$ TeV, we expect about $5000$ positively charged $τ^+ τ^+$ events via $pp \to ϕ_3 ϕ_3 \to τ^+ τ^+ + 2 \cdot j_b$ ($j_b$=b-jet) at the 13 TeV LHC with an integrated luminosity of 300 fb$^{-1}$. It is interesting to note that, in the LQ EFT framework, the expected same-sign lepton signals have a rate which is several times larger than the QCD LQ-mediated opposite-sign leptons signals, $gg,q \bar q \to ϕ_3 ϕ_3^* \to \ell^+ \ell^- +X$. We also consider the same-sign charged lepton signals in the LQ EFT framework at higher energy hadron colliders such as a 27 TeV HE-LHC and a 100 TeV FCC-hh.

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arXiv2019

R-Parity Violating Supersymmetry and the 125 GeV Higgs signals

We study the impact of R-parity violating Supersymmetry (RPV SUSY) on the 125 GeV Higgs production and decay modes at the LHC. We assume a heavy SUSY spectrum with multi-TeV squarks and SU(2) scalar singlets as well as the decoupling limit in the SUSY Higgs sector. In this case the lightest CP-even Higgs is SM-like when R-parity is conserved. In contrast, we show that when R-parity violating interactions are added to the SUSY framework, significant deviations may occur in some production and decay channels of the 125 GeV Higgs-like state. Indeed, we assume a single-flavor (mostly third generation) Bilinear RPV (BRPV) interactions, which generate Higgs-sneutrino mixing, lepton-chargino mixing and neutrino-neutralino mixing, and find that notable deviations of ${\cal O}(20-30\%)$ may be expected in the Higgs signal strength observables in some channels, e.g., in $p p \to h \to μ^+ μ^-, τ^+ τ^-$. Moreover, we find that new and detectable signals associated with BRPV Higgs decays to gauginos, $h\rightarrowν_τ\tildeχ_{2}^{0}$ and $h\rightarrowτ^{\pm}χ_{2}^{\mp}$, may also arise in this scenario. These decays yield a typical signature of $h \to τ^\pm \ell^\mp + {\not\!\! E_T}$ ($\ell =e,μ,τ$) that can be much larger than in the SM, and may also be accompanied by an ${\cal O}(20-30\%)$ enhancement in the di-photon signal $pp \to h \to γγ$. We also examine potential interesting signals of Trilinear R-parity violation (TRPV) interactions in the production and decays of the Higgs-sneutrino BRPV mixed state (assuming it is the 125 GeV scalar) and show that, in this case also, large deviations up to ${\cal O}(100\%)$ are expected in e.g., $p p \to h \to μ^+ μ^-, τ^+ τ^-$, which are sensitive to the BRPV$\times$TRPV coupling product.

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arXiv2018

A universally enhanced light-quarks Yukawa couplings paradigm

We propose that natural TeV-scale new physics (NP) with ${\cal O}(1)$ couplings to the standard model (SM) quarks may lead to a universal enhancement of the Yukawa couplings of all the light quarks, perhaps to a size comparable to that of the SM b-quark Yukawa coupling, i.e., $y_q \sim {\cal O}(y_b^{SM})$ for $q=u,d,c,s$. This scenario is described within an effective field theory (EFT) extension of the SM, for which a potential contribution of certain dimension six effective operators to the light quarks Yukawa couplings is $y_q \sim {\cal O} \left( f \frac{v^2}{Λ^2} \right)$, where $v$ is the Higgs vacuum expectation value (VEV), $v=246$ GeV, $Λ$ is the typical scale of the underlying heavy NP and $f$ is the corresponding Wilson coefficient which depends on its properties and details. In particular, we study the case of $y_q \sim 0.025 \sim y_b^{SM}$, which is the typical size of the enhanced light-quark Yukawa couplings if the NP scale is around $Λ\sim 1.5$ TeV and the NP couplings are natural, i.e., $f \sim {\cal O}(1)$. We also explore this enhanced light quarks Yukawa paradigm in extensions of the SM which contain TeV-scale vector-like quarks and we match them to the specific higher dimensional effective operators in the EFT description. We discuss the constraints on this scenario and the flavor structure of the underlying NP dynamics and suggest some resulting "smoking gun" signals that should be searched for at the LHC, such as multi-Higgs production $pp \to hh,hhh$ and single Higgs production in association with a high $p_T$ jet ($j$) or photon $pp \to hj,h γ$ and with a single top-quark $pp \to h t$.

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arXiv2018

Light-quarks Yukawa couplings and new physics in exclusive high-$p_T$ Higgs + jet and Higgs + $b$-jet events

We suggest that the exclusive Higgs + light (or b)-jet production at the LHC, $pp \to h+j(j_b)$, is a rather sensitive probe of the light-quarks Yukawa couplings and of other forms of new physics (NP) in the Higgs-gluon $hgg$ and quark-gluon $qqg$ interactions. We study the Higgs $p_T$-distribution in $pp \to h+j(j_b) \to γγ+ j(j_b)$, i.e., in $h+j(j_b)$ production followed by the Higgs decay $h \to γγ$, employing the ($p_T$-dependent) signal strength formalism to probe various types of NP which are relevant to these processes and which we parameterize either as scaled Standard Model (SM) couplings (the kappa-framework) and/or through new higher dimensional effective operators (the SMEFT framework). We find that the exclusive $h+j(j_b)$ production at the 13 TeV LHC is sensitive to various NP scenarios, with typical scales ranging from a few TeV to ${\cal O}(10)$ TeV, depending on the flavor, chirality and Lorentz structure of the underlying physics.

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arXiv2016

Implementation of the left-right symmetric model in FeynRules

We present an implementation of the manifest left-right symmetric model in FeynRules. The different aspects of the model are briefly described alongside the corresponding elements of the model file. The model file is validated and can be easily translated to matrix element generators such as MadGraph5_aMC@NLO, CalcHEP, Sherpa, etc. The implementation of the left-right symmetric model is a useful step for studying new physics signals with the data generated at the LHC.

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arXiv2016

Contact Interactions in Higgs-Vector Boson Associated Production at the ILC

We explore new physics (NP) effects in Higgs-Vector boson associated production at a future International Linear Collider (ILC) via e+e- -> Zh,Zhh, using effective field theory (EFT) techniques. In particular, we focus on a certain class of dimension 6 operators, which are generated by tree-level exchanges of a new heavy vector field in the underlying theory. These operators induce new contact terms of the form ψψϕDϕ, involving the Standard Model (SM) fermions (ψ), gauge-bosons (D is the covariant derivative) and the SM Higgs field (ϕ). We investigate the high-energy behaviour of these new effective interactions in e+e- -> Zh,Zhh, imposing bounds from electroweak precision measurements, and show that the ILC is an excellent testing ground for probing this type of NP via e+e- -> Zh,Zhh. We also address the validity of the EFT expansion and we study the correlation between the hZ and hhZ signals, which can be utilized in future searches for NP in these channels.

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arXiv2016

Chiral heavy fermions in a two Higgs doublet model: 750 GeV resonance or not

We revisit models where a heavy chiral 4th generation doublet of fermions is embedded in a class of two Higgs doublets models (2HDM) with a discrete $Z_2$ symmetry, which couples the "heavy" scalar doublet only to the 4th generation fermions and the "light" one to the Standard Model (SM) fermions - the so-called 4G2HDM introduced by us several years ago. We study the constraints imposed on the 4G2HDM from direct searches of heavy fermions, from precision electroweak data (PEWD) and from the measured production and decay signals of the 125 GeV scalar, which in the 4G2HDM corresponds to the lightest CP-even scalar h. We then show that the recently reported excess in the $γγ$ spectrum around 750 GeV can be accommodated by the heavy CP-even scalar of the 4G2HDM, H, resulting in a unique choice of parameter space: negligible mixing (sinα~ O(0.001)) between the two CP-even scalars h,H and heavy 4th generation quark and lepton masses m_t',m_b' < 400 GeV and $m_{ν'},m_{τ'}$ > 900 GeV, respectively. Whether or not the 750 GeV γγresonance is confirmed, interesting phenomenology emerges in q' - Higgs systems (q'=t',b'), that can be searched for at the LHC. For example, the heavy scalar states of the model, S=H,A,H^+, may have BR(S -> q'q') ~ O(1), giving rise to observable q'q' signals on resonance, followed by the flavor changing q' decays t'->uh (u=u,c) and/or b'->dh (d=d,s,b). This leads to distinct high jet-multiplicity signatures, with or without charged leptons, of the form q'q' -> (nj + mb + lW)_S (j and b being light and b-quark jets, respectively), with n+m+l =6-8 and unique kinematic features. It is also shown that the 4G2HDM can easily accommodate the interesting recent indications of a percent-level branching ratio in the lepton-flavor-violating (LFV) decay $h \to τμ$ of the 125 GeV Higgs, if confirmed.

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arXiv2015

EFT naturalness: an effective field theory analysis of Higgs naturalness

Assuming the presence of physics beyond the Standard Model (SM) with a characteristic scale M ~ O(10) TeV, we investigate the naturalness of the Higgs sector at scales below M using an effective field theory (EFT) approach. We obtain the leading 1-loop EFT contributions to the Higgs mass with a Wilsonian-like hard cutoff, and determine the constraints on the corresponding operator coefficients for these effects to alleviate the little hierarchy problem up to the scale of the effective action Λ< M, a condition we denote by "EFT-naturalness". We also determine the types of physics that can lead to EFT-naturalness and show that these types of new physics are best probed in vector-boson and multiple-Higgs production. The current experimental constraints on these coefficients are also discussed.

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arXiv2014

Softening Higgs Naturalness - an EFT Analysis

We investigate naturalness in the Standard Model (SM) Higgs sector using effective field theory (EFT) techniques and find the requirements on the new heavy physics that can potentially cure the little hierarchy problem below a scale $Λ\gg O(1 ~{\rm TeV})$, assuming the new heavy particles have a mass larger than $ Λ$. In particular, we determine the conditions under which the 1-loop corrections to $ m_h $ from the heavy new physics can balance those created by SM loop effects up to the naturalness scale $Λ$, a condition we denote by "EFT Naturalness". We obtain the higher dimensional ($n \ge 5$) operators in the effective Lagrangian that can lead to EFT Naturalness, and classify the underlying heavy theories that can generate such operators at tree-level. We also address the experimental constraints on our EFT Naturalness setup and discuss the expected experimental signals of the new heavy physics associated with EFT Naturalness.

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