We construct a minimal calculable model of a light dilaton based on the scenario where only top and Higgs sectors are involved in a quasiconformal dynamics. The model consistently accommodates the electroweak precision tests even when the Higgs boson is very heavy, thereby allowing one to consider the possibility that the particle at around 125GeV, discovered at the LHC experiments, is identified as the light dilaton rather than the Higgs boson. We find that the current LHC data allow distinct parameter regions where the observed particle is either mostly the Higgs boson or the dilaton.
In this talk I argue that a light techni-dilaton exists in models of walking technicolor near the conformal window. The light techni-dilaton then mixes with the composite Higgs, which is predicted to be narrow and light in walking technicolor models. It is an interesting possibility that the newly discovered boson at LHC might be a mixed state of techni-dilaton and the composite Higgs.
We study soft wall models that can embed the Standard Model and a naturally light dilaton. Exploiting the full capabilities of these models we identify the parameter space that allows to pass Electroweak Precision Tests with a moderate Kaluza-Klein scale, around $2$ TeV. We analyze the coupling of the dilaton with Standard Model (SM) fields in the bulk, and discuss two applications: i) Models with a light dilaton as the first particle beyond the SM pass quite easily all observational tests even with a dilaton lighter than the Higgs. However the possibility of a 125 GeV dilaton as a Higgs impos…
The dilaton, a pseudo-Nambu-Goldstone boson appearing in spontaneous scale symmetry breaking at a TeV scale f, may be found in Higgs boson searches. The dilaton couples to standard model fermions and weak bosons with the same structure as the Higgs boson except for the overall strength. Additionally, the dilaton couples to a Higgs boson pair. The couplings of the dilaton to a gluon pair and a photon pair, appearing at loop level, are largely enhanced compared to the corresponding Higgs couplings. We present regions of the mass and VEV of the dilaton allowed by WW, ZZ, and gammagamma limits fro…
We study the extension of the Standard Model (SM) with a light dilaton in a five dimensional warped model. In particular, we analyze the coupling of the dilaton with the SM matter fields, compare the model predictions with Electroweak Precisions Tests and find the corresponding bounds on the mass of the lightest Kaluza-Klein modes. We also investigate the possibility that the Higgs-like resonance found at the LHC can be a dilaton. Finally, we show that our set-up can also provide an explanation of the anomalies recently observed in $B$-meson decays.
The Standard Model Higgs searches using the first 1-2 fb-1 of LHC data can be used to put interesting constraints on new scalar particles other than the Higgs. We investigate one such scenario in which electroweak symmetry is broken via strongly coupled conformal dynamics. This scenario contains a neutral scalar dilaton---the Goldstone boson associated with spontaneously broken scale invariance---with a mass below the conformal symmetry breaking scale and couplings to Standard Model particles similar (but not identical) to those of the Standard Model Higgs boson. We translate the LEP and LHC H…
The existence of a dilaton as a pseudo-Nambu-Goldstone boson in spontaneous breaking of scale symmetry is predicted in beyond standard model theories in which electroweak symmetry is broken via strongly coupled conformal dynamics. Such a particle is expected to have a mass below the conformal symmetry breaking scale $f$ and couplings to standard model particles similar to those of the SM Higgs boson. In this paper we estimate, for the first time, the dilaton production in exclusive processes considering Pomeron - Pomeron ($\pom \pom$) and photon - photon ($γγ$) interactions, which are characte…
In this paper, we explore the possibility that a light dilaton can be the first sign of new physics at the LHC. The dilaton could emerge in approximate scale invariant UV completions of the SM as the Goldstone boson associated with the spontaneous breaking of the scale invariance. We study in detail the phenomenology of the dilaton at the LHC in the mass range of [$10-300$] GeV including the case where the dilaton can mix with the SM Higgs boson, leading to an interesting interplay between direct and indirect constraints. A possibility that the dilaton acts as a portal to a dark sector is also…
A new particle at around 125 GeV has been observed at the LHC, which we show could be identified with the techni-dilaton (TD) predicted in the walking technicolor and thus should be an evidence of walking technicolor. The TD is a pseudo Nambu-Goldstone boson for the approximate scale symmetry spontaneously broken by techni-fermion condensation, with its lightness being ensured by the approximate scale invariance of the walking technicolor. We test the goodness-of-fit of the TD signatures using the presently available LHC data set, and show that the 125 GeV TD is actually favored by the current…
We analyze the decays to muons of a light dilaton produced via vector boson fusion at the LHC. We investigate models in which the electroweak symmetry breaking is triggered by a spontaneously broken, approximately conformal sector. Taking into account the possibility of shifts in the dilaton Yukawa couplings to muons, we find a rather promising scenario for the conformal model search in the channel, with the possibility for a dilaton discovery at a delivered luminosity of 100 fb-1 at the LHC or, alternatively, for an extension of the exclusion zone in the model parameter space, until now fixed…
We consider the Higgs-dilaton(radion) system using the trace of energy-momentum tensor ($T_{~μ}^μ$) with the full Standard Model (SM) gauge symmetry $G_{\rm SM} \equiv SU(3)_c \times SU(2)_L \times U(1)_Y$, and find out that the resulting phenomenology for the Higgs-dilaton(radion) system is distinctly different from the earlier studies based on the $T_{~μ}^μ$ with the unbroken subgroup $H_{\rm SM} \equiv SU(3)_c \times U(1)_{\rm em}$ of $G_{\rm SM}$. After electroweak symmetry breaking (EWSB), the SM Higgs boson and dilaton(radion) will mix with each other, and there appear two Higgs-like sca…
Techni-dilaton (TD) is predicted in walking technicolor (WTC) arising as a pseudo Nambu-Goldstone boson associated with the approximate scale symmetry spontaneously broken by techni-fermion condensation. The TD mass is therefore smaller than those of other techni-hadrons on order of several TeVs, small enough to be within reach of the current LHC search. We present a new method to derive the TD couplings directly from the Ward-Takahashi identities, which enables us to explicitly calculate the quantities relevant to the TD LHC signatures. To set definite benchmarks, we take one-doublet and one-…
The Minimal Dilaton Model (MDM) extends the Standard Model (SM) by a singlet scalar, which can be viewed as a linear realization of general dilaton field. This new scalar field mixes with the SM Higgs field to form two mass eigenstates with one of them corresponding to the 125 GeV SM-like Higgs boson reported by the LHC experiments. In this work, under various theoretical and experimental constrains, we perform fits to the latest Higgs data and then investigate the phenomenology of Higgs boson in both the heavy dilaton scenario and the light dilaton scenario of the MDM. We find that: (i) If on…
Confront a dilaton model with the LHC measurements
School of Physics Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Center for Future High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理前沿中心）
We explore the potential for the discovery of a dilaton $\mathcal{O}(200-500)$ GeV in a classical scale/conformal invariant extension of the Standard Model by investigating the size of the corresponding breaking scale $Λ$ at the LHC, extending a previous analysis. In particular, we address the recent bounds on $Λ$ derived from Higgs boson searches. We investigate if such a dilaton can be produced via gluon-gluon fusion, presenting rates for its decay either into a pair of Higgs bosons or into two heavy gauge bosons, which can give rise to multi-leptonic final states. A detailed analysis via PY…
We study a scenario in which the dilaton, a pseudo-Goldstone boson of the spontaneous breaking of conformal symmetry, provides a portal between dark matter and the visible sector. We consider the low-energy description of the theory in which the dilaton mixes with the Standard Model Higgs boson, thereby predicting a second scalar at or above the weak scale. We derive the collider and dark matter constraints on the corresponding parameter space and find that existing experimental data point towards the decoupling limit in which the CFT scale is well above the electroweak scale. Moreover, the th…
We analyse the current status of the dilaton domination scenario in the MSSM and its singlet extensions taking into account the measured value of the Higgs mass, the relic abundance of dark matter and constraints from SUSY searches at the LHC. We find that in the case of the MSSM the requirement of a dark matter relic abundance in accord with observation severely restricts the allowed parameter space, implying an upper bound on the superpartner masses which makes it fully testable at LHC-14. In singlet extensions with a large singlet-MSSM coupling $λ$ as favoured by naturalness arguments the c…
Five-dimensional geometries with a linearly varying dilaton background arise as gravity duals of TeV Little String Theories (LSTs) and provide a solution of the hierarchy problem through extra dimensions. The unique Kaluza-Klein graviton spectrum has a mass gap on the order of the dilaton slope followed by a closely spaced discretum of states. We study in detail the graviton phenomenology in this scenario, allowing the dilaton slope to vary from the MeV to the TeV scale. When the dilaton slope is large enough so that individual KK resonances can be resolved at the LHC, several of them can be d…
Motivated by the bulk mixing $ξR_5 H^{\dagger}H$ between a massive radion and a bulk scalar Higgs in warped extra dimensions, we construct an effective four dimensional action that---via the AdS/CFT correspondence---describes the most general mixing between the only light states in the theory, the dilaton and the Higgs. Due to conformal invariance, once the Higgs scalar is localized in the bulk of the extra-dimension the coupling between the dilaton and the Higgs kinetic term vanishes, implying a suppressed coupling between the dilaton and massive gauge bosons. We comment on the implications o…
We consider a strongly interacting twin Higgs (SITH) model where an ultraviolet completion of twin Higgs mechanism is realized by a strongly coupled approximately scale invariant theory. Besides the Standard Model (SM) and twin sectors, the low energy effective theory contains a relatively light scalar called a dilaton --- the pseudo Goldstone boson of spontaneously broken scale invariance. The dilaton provides a unique portal between the SM and twin sectors whose phenomenology could provide an important probe of the twin Higgs mechanism. As a concrete example, we consider a holographic twin H…
Walking technicolor predicts a light composite scalar, techni-dilaton, arising as a pseudo Nambu-Goldstone boson for the approximate scale symmetry spontaneously broken by techni-fermion condensation. We show that a light techni-dilaton with mass of around 125 GeV can explain presently observed excesses particularly in the di-photon decay channel at LHC.
In light of the recent 750 GeV diphoton excesses reported by the ATLAS and CMS collaborations, we investigate the possibility of explaining this excess using the Minimal Dilaton Model. We find that this model is able to explain the observed excess with the presence of additional top partner(s), with same charge as the top quark, but with mass in the TeV region. First, we constrain model parameters using in addition to the 750 GeV diphoton signal strength, precision electroweak tests, single top production measurements, as well as Higgs signal strength data collected in the earlier runs of the …
We try to interpret the 750 GeV diphoton excess in the Minimal Dilaton Model, which extends the SM by adding one linearized dilaton field and vector-like fermions. We first show by analytic formulae in this framework that the production rates of the $γγ$, $gg$, $Zγ$, $ZZ$, $WW^\ast$, $t\bar{t}$ and $hh$ signals at the $750 {\rm GeV}$ resonance are only sensitive to the dilaton-Higgs mixing angle $θ_S$ and the parameter $η\equiv v N_X/f$, where $f$ is the dilaton decay constant and $N_X$ denotes the number of the fermions. Then we scan the two parameters by considering various theoretical and e…
We explore discovery signatures of techni-dilaton (TD) at LHC. The TD was predicted long ago as a composite pseudo Nambu-Goldstone boson (pNGB) associated with the spontaneous breaking of the approximate scale symmetry in the walking technicolor (WTC). Being pNGB, whose mass arises from the explicit scale-symmetry breaking due to the dynamical mass generation, the TD should have a mass MTD lighter than other techni-hadrons, say MTD \simeq 600GeV for the typical WTC model, which is well in the discovery range of the ongoing LHC experiment. We develop a spurion method of nonlinear realization to…
We present discovery signatures of techni-dilaton (TD) at LHC. The TD was predicted long ago as a pseudo Nambu-Goldstone boson (pNGB) associated with the spontaneous breaking of the approximate scale symmetry in the walking technicolor (WTC) (initially dubbed "scale-invariant technicolor"). Being pNGB, the TD should have a mass M_TD lighter than other techni-hadrons like techni-rho meson; It has recently been estimated to be M_TD ~= 500-600 GeV for the typical WTC model, which is well in the discovery range of the ongoing LHC experiment. Noting that all the TD couplings to the standard model (…
Whether an additional light scalar exists is an interesting topic beyond the Standard Model (SM), while nowadays we do not know exactly physics beyond the SM in the low mass region, e.g., the Atlas and CMS collaborations get inconsistent results at around 95 GeV in searching for light resonances in diphoton channel. Considering these, we study a light scalar in the Minimal Dilaton Model (MDM). Under the theoretical and latest experimental constraints, we sort the surviving samples into two scenarios according to the diphoton rate of the light scalar: the large-diphoton scenario (with $/SM\gtrs…
A holographic model of probe quarkonia is presented, where the dynamical gravity-dilaton background is adjusted to the thermodynamics of 2 +1 flavor QCD with physical quark masses. The quarkonia action is modified to account for a systematic study of the heavy-quark mass dependence. We focus on the $J/ψ$ and $Υ$ spectral functions and relate our model to heavy quarkonia formation as a special aspect of hadron phenomenology in heavy-ion collisions at LHC.
It has been pointed out recently that the presence of dilaton field in the early Universe can dilute the neutralino dark matter (DM) abundance, if Universe is not radiation dominated at DM decoupling, due to its dissipative-like coupling to DM. In this scenario two basic mechanisms compete, the modified Hubble expansion rate tending to increase the relic density and a dissipative force that tends to decrease it. The net effect can lead to an overall dramatic decrease of the predicted relic abundance, sometimes by amounts of the order of O(10^2) or so. This feature is rather generic, independen…
We discuss the presence of a light dilaton in Conformal Field Theories deformed by a single scalar operator, in the holographic realization consisting of confining Renormalization Group flows. Then, we apply this formalism to study the extension of the Standard Model with a light dilaton in a 5D warped model. We study the spectrum of scalar and vector perturbations, compare the model predictions with Electroweak Precision Tests and find the corresponding bounds for the lightest modes. Finally, we analyze the possibility that the Higgs resonance found at the LHC be a dilaton.
The 125 GeV boson is quite consistent with the Higgs boson of the Standard Model (SM), but there is a challenge from Anderson whether this particle is in the Lagrangian. As LHC Run 2 takes its final year of running, we ought to reflect and make sure we have gotten everything right. The ATLAS and CMS combined Run 1 analysis claims 5.4$σ$ measurement of vector boson fusion (VBF) production that is consistent with SM, which seemingly refutes Anderson. However, to verify the source of electroweak symmetry breaking (EWSB), we caution that VBF measurement is too important for us to be imprudent in a…
We consider the model containing a dilaton vs Higgs boson in the nearly conformal sector (NCS). The potential of a dilaton in NCS is linearly rising with distances. The light scalar dilaton would be one of the best candidates to explain the LHC data in recent discovery of a Higgs-like resonance at 125 GeV.
A number of candidate theories beyond the standard model (SM) predict new scalar bosons below the TeV region. Among these, the radion, which is predicted in the Randall-Sundrum model, and the dilaton, which is predicted in spontaneous scale symmetry breaking, have very similar couplings to those of the SM Higgs boson, and it is very difficult to differentiate these three spin-0 particles in the expected signals of the Higgs boson at the LHC and Tevatron. We demonstrate that the observation of the ratio sigma(gamma gamma)/sigma(WW) gives a simple and decisive way, independently of the values of…
We re-examine the feasibility of the higgs-like particle discovered at the LHC being a dilaton: the Goldstone boson of spontaneous breaking of scale invariance. We review the expected phenomenological deviations from the SM higgs and compare with other Goldstone higgs scenarios, with particular emphasis on double higgs production.
We analyze the existence of a dilaton in gauge theories with approximate infrared conformal symmetry. To the extent that these theories are governed in the infrared by an approximate fixed point (walking), the explicit breaking of the conformal symmetry at these scales is vanishingly small. If confinement and spontaneous chiral-symmetry breaking set in at some infrared scale, the resultant breaking of the approximate conformal symmetry can lead to the existence of a dilaton with mass parametrically small compared to the confinement scale, and potentially observable at the LHC.
Both the ATLAS and CMS experiments at the LHC have reported the observation of the particle of mass around 125GeV which is consistent to the Standard Model (SM) Higgs boson, but with an excess of events beyond the SM expectation in the diphoton decay channel at each of them. There still remains room for a logical possibility that we are not seeing the SM Higgs but something else. Here we introduce the minimal dilaton model in which the LHC signals are explained by an extra singlet scalar of the mass around 125GeV that slightly mixes with the SM Higgs heavier than 600GeV. When this scalar has a…
We find that a holographic walking technicolor model has a limit ("conformal limit") where the techni-dilaton (TD) becomes an exactly massless Nambu-Goldstone boson of the scale symmetry with its nonzero finite decay constant F_phi /= 0, which naturally realizes a light TD, say at 125 GeV, near the limit. In such a light TD case, we find that F_phi is uniquely determined by the techni-pion decay constant F_pi independently of the holographic parameters: F_phi/F_pi ~= sqrt{2 N_TF}, with N_TF being the number of techni-fermions. We show that the holographic TD is consistent with a new boson at 1…
We study very light dilaton, arising from a scale-invariant ultraviolet theory of the Higgs sector in the standard model of particle physics. Imposing the scale symmetry below the ultraviolet scale of the Higgs sector, we alleviate the fine-tuning problem associated with the Higgs mass. When the electroweak symmetry is spontaneously broken radiatively à la Coleman-Weinberg, the dilaton develops a vacuum expectation value away from the origin to give an extra contribution to the Higgs potential so that the Higgs mass becomes naturally around the electroweak scale. The ultraviolet scale of the H…
We analyze in detail the phenomenology of a model of dynamical electroweak symmetry breaking inspired by walking technicolor, by using the techniques of the bottom-up approach to holography. The model admits a light composite scalar state, the dilaton, in the spectrum. We focus on regions of parameter space for which the mass of such dilaton is 125 GeV, and for which the bounds on the precision electroweak parameter S are satisfied. This requires that the next-to-lightest composite state is the techni-rho meson, with a mass larger than 2.3 TeV. We compute the couplings controlling the decay ra…
We consider the minimal Standard Model as an effective low-energy description of an unspecified fundamental theory with spontaneously broken conformal symmetry. The effective theory exhibits classical scale invariance which manifest itself through the dilaton field. The mass of the dilaton is generated via the quantum scale anomaly at two-loop level and is proportional to the techically stable hierarchy between the electroweak scale and a high energy scale given by a dilaton vacuum expectation value. We find that a generic prediction of this class of models is the existence of a very light dil…
We investigate the properties of the radion in the 5D linear dilaton model arising from Little String Theory. A Goldberger-Wise type mechanism is used to stabilise a large interbrane distance, with the dilaton now playing the role of the stabilising field. We consider the coupled fluctuations of the metric and dilaton fields and identify the physical scalar modes of the system. The wavefunctions and masses of the radion and Kaluza-Klein modes are calculated, giving a radion mass of order the curvature scale. As a result of the direct coupling between the dilaton and Standard Model fields, the …
The non-minimal Higgs-gravity coupling, $ξH^\dagger H R$, can play an interesting role in particle physics. We utilize the available LHC Run-2 data to obtain the bound on the coupling $ξ$ and discuss the prospects of constraining it at CEPC, FCC-ee and ILC. Also, we investigate its implication on the naturalness.
We investigate the Higgs-strahlung production process e^+ e^- \to Z h at the future Higgs factory such as TLEP by including radiative corrections in the Minimal Dilaton Model (MDM), which extends the SM by one singlet scalar called dilaton. We consider various theoretical and experimental constraints on the model, and perform fits to the Higgs data taken from ATLAS, CMS and CDF+D0. Then for the 1σsurviving samples, we calculate the MDM predictions on the inclusive production rate σ(e^+e^-\to Zh) at the 240-GeV Higgs factory, and also the signal rates of e^+e^-\to Zh with the Higgs boson decayi…
Among various supersymmetric (SUSY) standard models, the gravity mediation model with a neutralino LSP and the gauge mediation model with a very light gravitino are attractive from the cosmological view point. These models have different scales of SUSY breaking and their underlying physics in high energy is quite different. However, if the sparticles' decay into the gravitino is prompt in the latter case, their collider signatures can be similar: multiple jets and missing transverse momentum. In this paper, we study the discrimination between these models in minimal cases at the LHC based on t…
A Higgs-like dilaton owns couplings that differ from those of the Standard Model Higgs and of a generic Composite Higgs. The complete bosonic basis for a Higgs-like dilaton is presented at the first subleading order. A comparison with the Standard Model, the Standard Model Effective Field Theory and the generic Lagrangian for the minimal $SO(5)/SO(4)$ Composite Higgs model is performed. Observables that can disentangle the different hypotheses are identified.
Effective Field Theory Description of Light Dilaton
Peking University（北京大学）；Zhengzhou University（郑州大学）；Center for High Energy Physics, Peking University（北京大学高能物理中心）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Hangzhou Institute for Advanced Study, UCAS（中国科学院大学杭州高等研究院）
We propose simple freeze-in models where the observed dark matter abundance is explained via the decay of an electrically charged and/or coloured parent particle into Feebly Interacting Massive Particles (FIMP). The parent particle is long-lived and yields a wide variety of LHC signatures depending on its lifetime and quantum numbers. We assess the current constraints and future high luminosity reach of these scenarios at the LHC from searches for heavy stable charged particles, disappearing tracks, displaced vertices and displaced leptons. We show that the LHC constitutes a powerful probe of …
