We perform a multivariate analysis of Higgs-pair production in $HH \to b\bar b γγ$ channel at the HL-LHC to probe the trilinear Higgs self--coupling $λ_{3H}$, which takes the value of 1 in the SM. We consider all the known background processes. Also, for the signal we are the first to adopt the most recent event generator of POWHEG-BOX-V2 to exploit the NLO distributions for Toolkit for Multivariate Data Analysis (TMVA), taking account of the full top--quark mass dependence. Through Boosted Decision Tree (BDT) analysis trained for $λ_{3H}=1$, we find that the significance can reach up to 1.95 with about $9$ signal and $18$ background events. In addition, the Higgs boson self-coupling can be constrained to $1.00 < λ_{3H} < 6.22$ at 95\% confidence level (CL). We also perform a likelihood fitting of $M_{γγbb}$ distribution and find the $1σ$ confidence interval (CI) of $0.1 < λ_{3H} < 2.2\, \cup\,5.4 < λ_{3H} < 6.6$ for the $λ_{3H}=1$ nominal set. On the other hand, using BDTs trained for each value of $λ_{3H}$, we find a bulk region of $0.5 <\sim λ_{3H} <\sim~ 4.5$, for which it is hard to pin down the trilinear coupling.
We present results for Higgs boson pair production with variations of the trilinear Higgs boson self-coupling at next-to-leading order (NLO) in QCD including the full top quark mass dependence. Differential results at 14 TeV are presented, and we discuss the implications of anomalous trilinear couplings as well as differences between the PYTHIA 8.2 and HERWIG 7.1 parton showers in combination with POWHEG. The implementation of the NLO QCD calculation with variable Higgs boson self-coupling is made publicly available in the POWHEG-BOX-V2 Monte Carlo framework. A simple method for using the new …
A direct measurement of the trilinear $WWγ$ and $WWZ$ couplings is possible in the pair production of electroweak bosons at $e^+e^-$ and hadron colliders. This talk addresses some of the theoretical issues: the parameterization of ``anomalous couplings'' in terms of form factors and effective Lagrangians, the complementary information which can be obtained in $e^+e^-$ vs. hadron collider experiments, and a novel way to implement finite $W$-width effects in a gauge invariant manner.
We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous trilinear vector-boson interactions W^+ W^- γand W^+ W^- Z through the single production of electroweak gauge bosons via the weak boson fusion processes q q -> q q W (-> \ell^\pm ν) and q q -> q q Z(-> \ell^+ \ell^-) with \ell = e or μ. After a careful study of the standard model backgrounds, we show that the single production of electroweak bosons at the LHC can provide stringent tests on deviations of these vertices from the standard model prediction. In particular, we show that single gauge boson production …
We perform a multivariate analysis of Higgs-pair production via the decay channel $HH \to b\bar b γγ$ at the future 100 TeV $pp$ collider to determine the trilinear Higgs self--coupling (THSC) $λ_{3H}$, which takes the value of 1 in the standard model. We consider all known background processes. For the signal we adopt the most recent event generator of {\tt POWHEG-BOX-V2} to exploit the NLO distributions for Toolkit for Multivariate Data Analysis (TMVA). Through the technique of Boosted Decision Tree (BDT) analysis trained for $λ_{3H}=1$, compared to the the conventional cut-and-count approac…
The determination of the Higgs self coupling is one of the key ingredients for understanding the mechanism behind the electroweak symmetry breaking. An indirect method for constraining the Higgs trilinear self coupling via single Higgs production at next-to-leading order (NLO) has been proposed in order to avoid the drawbacks of studies with double Higgs production. In this paper we study the Higgs self interaction through the vector boson fusion (VBF) process $e^{-} p \to ν_{e} h j$ at the future LHeC. At NLO level, we compute analytically the scattering amplitudes for relevant processes, in …
We propose a method to determine the trilinear Higgs self coupling that is alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production ($gg{\rm F}$, VBF, $WH$, $ZH$, $t\bar tH$) and decay ($γγ$, $WW^{*}/ZZ^{*}\to 4f$, $b\bar b$, $ττ$) modes at the LHC and then estimate the sensitivity to the trili…
The trilinear Higgs coupling $λ_{hhh}$ is crucial for determining the structure of the Higgs potential and for probing possible effects of physics beyond the Standard Model (SM). Focusing on the Two-Higgs-Doublet Model as a concrete example, we identify parameter regions in which $λ_{hhh}$ is significantly enhanced with respect to the SM. Taking into account all relevant corrections up to the two-loop level, we show that already current experimental bounds on $λ_{hhh}$ rule out significant parts of the parameter space that would otherwise be unconstrained. We illustrate the interpretation of t…
The Minimal Supersymmetric Standard Model (MSSM) can be extended to include non-holomorphic trilinear soft supersymmetry (SUSY) breaking interactions that may have distinct signatures. We consider non-vanishing off-diagonal entries of the coupling matrices associated with holomorphic (of MSSM) and non-holomorphic trilinear terms corresponding to sleptons with elements $A^l_{ij}$ and $A^{\prime l}_{ij}$. We first improve the MSSM charge breaking minima condition of the vacuum to include the off-diagonal entries $A^l_{ij}$ (with $i \neq j$). We further extend this analysis for non-holomorphic tr…
In the minimal supersymmetric standard model (MSSM), the μ-parameter and the trilinear coupling A_t may be generically complex and can affect various observables at B factories. Imposing the edm constraints, we find that there is no new large phase shift in the B^0 - \bar{B^0} mixing, CP violating dilepton asymmetry is smaller than 0.1 %, and the direct CP violation in B\to X_s γcan be as large as \sim \pm 16 %.
Specific models of supersymmetry breaking predict relations between the trilinear and bilinear soft supersymmetry breaking parameters A_0 and B_0 at the input scale. Models with A_0 = B_0 + m_0 as well as the simplest Polonyi model with A_0 = (3 - \sqrt{3}) m_0 are discussed. In such cases, the value of \tanb can be calculated as a function of the scalar masses m_0 and the gaugino masses m_{1/2}, and various experimental constraints can be applied to constrain it.
I first review a few basic guiding principles that lead to the notion of a hierarchy of couplings in searches of New Physics involving weak bosons processes. The hierarchies within a linear and a non-linear realization of symmetry breaking are compared to the usual {\em phenomenological} parameterization of the $WWV$ vertex. Limits that one expects to obtain at the NLC(500GeV) and LHC/SSC on the tri-linear and quadri-linear anomalous $W$ couplings are compared. The cleanness of an \epm gives the NLC a clear advantage in constraining the tri-linear couplings. However, with ``only" $500$GeV, the…
The flux of electron and positron cosmic rays measured by the space-based experiments PAMELA, AMS-02, CALET, DAMPE and Fermi-LAT shows an unexpected behaviour at high energies, in comparison with expectations from standard astrophysical sources. In particular, AMS-02 observations provide compelling evidence for a new source of positrons and electrons whose origin is still unknown. Plausible scenarios include either the contribution of dark matter or unresolved astrophysical sources, such as nearby pulsars. It has been shown that explanations based mostly on dark matter, tend to overproduce gam…
We study the potential of the next-generation $e^+ e^-$ linear colliders with longitudinally polarized beams, to restrict the values of the anomalous trilinear couplings $WWγ$ and $WWZ$ from the measurement of the process $e^+ e^-\to W^+ W^-$. Along with initial $e^+e^-$ polarization, we account also for the possibilities offered by cross sections for polarized final $W$, in order to disentangle the constraints on the various constants. The results show the essential role of the initial beams polarization in improving the bounds obtained from the unpolarized case.
New heavy neutral gauge bosons Z' are predicted by many models of physics beyond the Standard Model. It is quite possible that Z's are heavy enough to lie beyond the discovery reach of the CERN Large Hadron Collider LHC, in which case only indirect signatures of Z' exchanges may emerge at future colliders, through deviations of the measured cross sections from the Standard Model predictions. We discuss in this context the foreseeable sensitivity to Z's of W^\pm-pair production cross sections at the e^+e^- International Linear Collider (ILC), especially as regards the potential of distinguishin…
We analyze the potential of the e+e- Linear Colliders, operating in the e-gamma and gamma-gamma modes, to probe anomalous quartic vector--boson interactions through the multiple production of W's and Z's. We examine all $SU(2)_L \otimes U(1)_Y$ chiral operators of order p^4 that lead to new four--gauge--boson interactions but do not alter trilinear vertices. We show that the e-gamma and gamma-gamma modes are able not only to establish the existence of a strongly interacting symmetry breaking sector but also to probe for anomalous quartic couplings of the order of 10^{-2} at 90% CL. Moreover, t…
In extended Higgs sectors that exhibit alignment without decoupling, the additional scalars are allowed to have large couplings to the Standard Model Higgs. We show that current nonresonant di-Higgs searches can be straightforwardly adapted to look for additional Higgses in these scenarios, where pair production of non-SM Higgses can be enhanced. For concreteness, we study pair production of exotic Higgses in the context of an almost inert two Higgs doublet model, where alignment is explained through an approximate $\mathbb{Z}_2$ symmetry under which the additional scalars are odd. In this con…
We explore the use of polarized $e^+/e^-$ beams and/or the information on final state decay lepton polarizations in probing the interaction of the Higgs boson with a pair of vector bosons. A model independent analysis of the process $e^+ e^- \to f \bar f H$, where $f$ is any light fermion, is carried out through the construction of observables having identical properties under the discrete symmetry transformations as different individual anomalous interactions. This allows us to probe an individual anomalous term independent of the others. We find that initial state beam polarization can signi…
We present a fully differential next-to-next-to-leading order calculation of the Higgs pair production in association with a $Z$ boson, which is important for probing the trilinear Higgs self-coupling. The next-to-next-to-leading-order corrections enhance the next-to-leading order total cross sections by a factor of $1.2\sim 1.5$, depending on the collider energy, and change the shape of next-to-leading order kinematic distributions. We discuss how to determine the trilinear Higgs self-coupling using our results.
We explore the possible exotic particle content beyond the standard model by examining all its scalar bilinear combinations. We categorize these exotic scalar fields and show that without the suppression of (A) their Yukawa couplings with the known quarks and leptons, and (B) the trilinear couplings among themselves, most are already constrained to be very heavy from the nonobservation of proton decay and neutron-antineutron oscillations, the smallness of $K^0 - \bar {K^0}$, $D^0 - \bar {D^0}$ and $B_d^0 - \bar {B_d^0}$ mixing, as well as the requirement of a nonzero baryon asymmetry of the un…
In this analysis we explore the phenomenological constraints of models with non-holomorphic soft SUSY breaking terms in a beyond the MSSM scenario having identical particle content. The model referred as NHSSM shows various promising features like the possibility of a strong reduction in electroweak fine-tuning even for a scenario of a heavy higgsino type of LSP, a fact that is unavailable in pMSSM models. The other important aspect is satisfying the muon $g-2$ data even for a small $\tanβ$ via a small value of coupling $A_μ'$ associated with the tri-linear non-holomorphic soft term. Thus, a l…
We explore the challenging but phenomenologically interesting hierarchical mass spectrum of the Inert Doublet Model where relatively light dark matter along with much heavier scalar states can fully satisfy the constraints on the relic abundance and also fulfill other theoretical as well as collider and astrophysical bounds. To probe this region of parameter space at the LHC, we propose a signal process that combines up to two large radius boosted jets along with substantial missing transverse momentum. Aided by our intuitive signal selection, we capture a hybrid process where the di-fatjet si…
We perform a systematic study of the production of a third-generation fermion-pair, $μ^+μ^-\to f\bar{f}$ for $f=τ^-,b$, and t in the minimal supersymmetric standard model (MSSM) with explicit CP violation, which is induced radiatively by soft trilinear interactions related to squarks of the third generation. We classify all the observables for probing the CP property of the Higgs bosons constructed by the initial muon beam polarization along with the unpolarized final fermions and with the final-fermion polarization configuration of equal helicity, respectively. The observables allow for compl…
In the CP-violating Minimal Supersymmetric Standard Model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings $(A_t, A_b)$ and the gluino mass $(M_{\tilde g})$, e.g., $Φ_{\rm{CP}} = 60^\circ$ or $90^\circ$, for $M_{H^+} \lsim 140 $ GeV and $\tan β\sim 2-5 $, the lightest Higgs boson mass ($M_{H_1}$) is $\lsim 50 $ GeV. This mass interval is still allowed from standard LEP Higgs searches because of a strongly suppressed $H_1ZZ$ coupling. However, in the same region of parameter space in which these two conditions occur, the $H_1 H^\mp W^\pm $ co…
The measurement of Higgs pair production will be a cornerstone of the LHC program in the coming years. Double Higgs production provides a crucial window upon the mechanism of electroweak symmetry breaking and has a unique sensitivity to the Higgs trilinear coupling. We study the feasibility of a measurement of Higgs pair production in the $b\bar{b}b\bar{b}$ final state at the LHC. Our analysis is based on a combination of traditional cut-based methods with state-of-the-art multivariate techniques. We account for all relevant backgrounds, including the contributions from light and charm jet mis…
We have explored the prospect of probing a neutral scalar ($H$) produced in association with one $b$-quark and decaying either invisibly or into a pair of $b$-quarks at the LHC with centre of mass energy $\sqrt s = 14$ TeV. In this regard, we adopt an effective theory approach to parameterize a $Hb\bar bg$ vertex arising from a dimension six operator that encompasses the effect of some new physics setting in at a high scale. We concentrate solely on the five-flavor scheme to ascertain the sensitivity of the 14 TeV LHC in probing such an effective coupling as a function of the scalar mass at th…
The quartic self-coupling of the Standard Model Higgs boson can only be measured by observing the triple-Higgs production process, but it is challenging for the Large Hadron Collider (LHC) Run 2 or International Linear Collider (ILC) at a few TeV because of its extremely small production rate. In this paper, we present a detailed Monte Carlo simulation study of the triple-Higgs production through gluon fusion at a 100 TeV hadron collider and explore the feasibility of observing this production mode. We focus on the decay channel $HHH\rightarrow b\bar{b}b\bar{b}γγ$, investigating detector effec…
We study CP violation in the two-body decay of a scalar tau into a neutralino and a tau, which should be probed at the LHC and ILC. From the normal tau polarization, a CP asymmetry is defined which is sensitive to the CP phases of the trilinear scalar coupling parameter $A_τ$, the gaugino mass parameter $M_1$, and the higgsino mass parameter $μ$ in the stau-neutralino sector of the Minimal Supersymmetric Standard Model. Asymmetries of more than 70% are obtained in scenarios with strong stau mixing. As a result, detectable CP asymmetries in stau decays at the LHC are found, motivating further d…
We study the production of $t{\bar t}h$ and $t{\bar t}hh$ at hadron colliders, in the minimal Composite Higgs Models, based on the coset $SO(5)/SO(4)$. We explore the fermionic representations ${\bf 5}$ and ${\bf 14}$. A detailed phenomenological analysis is performed, covering the energy range of the LHC and its High Luminosity upgrade, as well as that of a future 100 TeV hadron collider. Both resonant and non-resonant production are considered, stressing the interplay and complementary interest of these channels with each other and double Higgs production. We provide sets of representative p…
The 95 GeV Excess in Models with Two Higgs Doublets plus One Singlet: Model Distinction via Four-top Final States and Triple Higgs Couplings
Instituto de Física Teórica (UAM/CSIC), Universidad Autónoma de Madrid（马德里自治大学理论物理研究所）；Shenzhen Campus of Sun Yat-sen University (SYSU)（中山大学深圳校区）；Deutsches Elektronen-Synchrotron DESY（德国电子同步辐射中心）；II. Institut für Theoretische Physik, Universität Hamburg（汉堡大学第二理论物理研究所）；Department of Physics and Astronomy, Ghent University（根特大学物理与天文学系）
We derive new limits on light stops from diboson resonance searches in the $γγ$, $Z γ$, $ZZ$, $WW$ and $hh$ channels from the first run of the LHC. If the two-body decays of the light stop are mildly suppressed or kinematically forbidden, stoponium bound states will form in $pp$ collisions and subsequently decay via the pair annihilation of the constituent stops to diboson final states, yielding striking resonance signatures. Remarkably, we find that stoponium searches are highly complementary to direct collider searches and indirect probes of light stops such as Higgs coupling measurements. U…
A measurement of the $hh+2j$ channel at the LHC would be particularly thrilling for electroweak physics. It is not only the leading process which is sensitive to the $W^+W^- hh$ and $ZZhh$ interactions, but also provides a potentially clear window to study the electroweak symmetry-breaking sector by probing Higgs-Goldstone interactions through the weak boson fusion component of the scattering process. Until now, a phenomenologically complete analysis of this channel has been missing. This is mostly due to the high complexity of the involved one-loop gluon fusion contribution and the fact that …
We perform the most up-to-date comprehensive signal-background analysis for Higgs-pair production in $HH \to b\bar b γγ$ channel at the HL-LHC and HL-100 TeV hadron collider, with the goal of probing the self-coupling $λ_{3H}$ of the Higgs boson. We simulate all the standard-model signal and background processes with the simulation tools almost as sophisticated as what experimentalists are using. We find that even for the most promising channel $HH \to b\bar{b}γγ$ at the HL-LHC with a luminosity of 3000 fb$^{-1}$, the significance is still not high enough to establish the Higgs self-coupling a…
Triple gauge boson production at the LHC can be used to test the robustness of the Standard Model and provide useful information for VBF di-boson scattering measurement. Especially, any derivations from SM prediction will indicate possible new physics. In this paper we present a detailed Monte Carlo study on measuring WWW production in pure leptonic and semileptonic decays, and probing anomalous quartic gauge WWWW couplings at the CERN LHC and future hadron collider, with parton shower and detector simulation effects taken into account. Apart from cut-based method, multivariate boosted decisio…
Assuming ALPs couple to gluons only, they can be produced via the $p p \to a j$ process and decay into two jets at the LHC. When the coupling parameter, $C_{\tilde{G}} / f_a$, is small, the lifetime of ALPs can be long enough leading to displaced final state jets. In this paper, we consider the signal including both the prompt and long-lived cases of ALPs by employing a specialized Delphes module to handle displaced jets. Relevant background processes are generated and simulated at the detector level, and multivariate analyses based on machine-learning are performed to discriminate signal and …
We investigate the prospective reach of the 14 TeV HL-LHC for resonant production of a heavy Higgs boson that decays to two SM-like Higgs bosons in the $4b$ final state in the scalar singlet extended Standard Model. We focus on the reach for choices of parameters yielding a strong first order electroweak phase transition. The event selection follows the $4b$ analysis by the ATLAS Collaboration, enhanced with the use of a boosted decision tree method to optimize the discrimination between signal and background events. The output of the multivariate discriminant is used directly in the statistic…
Probing the Electroweak Phase Transition in the Flipped Two-Higgs-Doublet Model at the LHC
Sun Yat-sen University（中山大学）；Guangdong Provincial Key Laboratory of Quantum Precision Measurement and Sensing（广东省量子精密测量与传感重点实验室）；Shenzhen Campus of Sun Yat-sen University（中山大学深圳校区）
We examine trilinear and quartic anomalous gauge couplings (AGCs) generated in composite Higgs models and models with warped extra dimensions. We first revisit the SU(2)_L x U(1)_Y effective Lagrangian and derive the charged and two-photon neutral AGCs. We derive the general perturbative contributions to the pure field-strength operators from spin 0, 1/2, 1 resonances by means of the heat kernel method. In the composite Higgs framework, we derive the pattern of expected deviations from typical SO(N) embeddings of the light composite top partner. We then study a generic warped extra dimension f…
Search for Quadruplet Scalars using Boosted Decision Trees at the LHC
SRM University-AP（SRM大学安得拉邦分校）；Chettinad Institute of Technology, Chettinad Academy of Research and Education（切蒂纳德理工学院，切蒂纳德研究与教育学院）；University of Delhi（德里大学）
