What kind of New Physics, if any, we expect to discover at the LHC? I will try to address this formidable question by re-formulating it as follows: is the breaking of the electroweak symmetry strong or weak ?
Composite Higgs models generically predict the existence of heavy spin-1 resonances with the same quantum numbers as electroweak gauge bosons. The effective lagrangian description of these resonances is presented, pointing out the origin of their interactions with SM matter fields and the resulting LHC phenomenology. Search strategies for spin-1 resonances are discussed, mentioning possible advantages offered by boosted decay products. The impact of interactions between spin-1 resonances and fermion resonances, crucial for the proper interpretation of LHC searches, is pointed out.
If the di-photon excess at 750 GeV hinted by the 2015 data at the LHC is explained in terms of a scalar resonance participating in the breaking of the electro-weak symmetry, this resonance must be accompanied by other scalar states for perturbative unitarity in vector boson scattering to be preserved. The simplest set-up consistent with perturbative unitarity and with the data of the di-photon excess is the Georgi-Machacek model.
Neutrino mass generation through the Higgs mechanism not only suggests the need to reconsider the physics of electroweak symmetry breaking from a new perspective, but also provides a new theoretically consistent and experimentally viable paradigm. We illustrate this by describing the main features of the electroweak symmetry breaking sector of the simplest type-II seesaw model with spontaneous breaking of lepton number. After reviewing the relevant "theoretical" and astrophysical restrictions on the Higgs sector, we perform an analysis of the sensitivities of Higgs boson searches at the ongoin…
The recent muon $g-2$ result from Fermilab combined with the Brookhaven result, strongly points to new physics beyond the Standard Model which can be well described by the electroweak sector of supersymmetry if the masses of the sleptons and some of the electroweak gauginos are in the few hundred GeV range. However, the Higgs boson mass measurement at 125 GeV indicates a mass scale for squarks which lies in the few TeV region indicating a split mass spectrum between squarks and sleptons. This apparent puzzle is resolved in a natural way in gluino-driven radiative breaking of the electroweak sy…
Combining anomaly with $Z^\prime$ mediation allows us to solve the tachyonic problem of the former and avoid fine tuning in the latter. This model includes an extra $U(1)^\prime$ gauge symmetry and extra singlet scalar $S$ which provides a solution to the `$μ$ problem' of the Minimal Supersymmetric Standard Model (MSSM). The low-energy particle spectrum is calculated from the UV inputs using the Renormalization Group Equations. The benchmark points considered in the original model, suggested before the Higgs discovery, predicted a Higgs mass heavier than the generic MSSM value. In 2012, the Hi…
We revisit the constraints on the parameter space of the Minimal Supersymmetric Standard Model (MSSM), from charge and color breaking minima in the light of information on the Higgs from the LHC so far. We study the behavior of the scalar potential keeping two light sfermion fields along with the Higgs in the pMSSM framework and analyze the stability of the vacuum. We find that for lightest stop $\lesssim 1$ TeV and small $μ\lesssim 500$ GeV, the absolute stability of the potential can be attained only for $|X_{t}| \lesssim \sqrt{ 6 m_{\tilde{t}_1} m_{\tilde{t}_2}}$. The bounds become stronger…
Low-scale supersymmetry breaking scenario in which the breaking scale is around TeV has been discussed as a possibility to obtain a large Higgs mass and to moderate the fine tuning problem. A characteristic feature is that the hidden sector would be accessible at colliders in such a scenario. In this paper, we investigate the phenomenology of sgoldstino which is the scalar component of the goldstino superfield. We present partial widths and branching ratios for sgoldstinos decaying to final states involving Higgs bosons and sparticles which have not been discussed in detail so far.
Supersymmetry and supergravity extend the standard model by introducing a new symmetry between fermions and bosons. Experimental data imply that supergravity must be broken. Among several mechanisms of supersymmetry breaking, gravity mediated supersymmetry breaking is central in this thesis. These mechanisms have the main feature to generate the so-called soft SUSY breaking terms. Recently, new solutions have been identified, leading to the usual soft breaking terms together with additional hard breaking terms. These new solutions are characterized by a new singlet chiral superfield with a non…
Discovering New Gauge Bosons of Electroweak Symmetry Breaking at LHC-8
我们研究了8 TeV大型强子对撞机(LHC-8)的物理潜力,在其2012年运行期间发现了一大类扩展规范模型或额外维模型,其低能行为可以用SU(2)^2 x U(1)规范结构很好地表示。我们分析了这类模型,发现在LHC-8的组合积分亮度为40-60/fb的情况下,当与Z玻色子一起产生时,可以发现W规范玻色子的第一个新的卡鲁扎-克莱因模式,其质量高达约370-400 GeV。
We propose a new way of breaking the Goldstone symmetry in composite Higgs models, restoring the global symmetry in the mixings between the elementary and composite fermions by completing the former to full representations of this symmetry. The Goldstone symmetry is in turn broken softly by vector-like mass terms in the {\it elementary} sector only. The resulting softened explicit breaking allows for a light Higgs boson, as found at the LHC, and a heavy top quark, without the need of light top partners around the Goldstone scale $f \sim {\rm TeV} \ll m_{\rm comp.}$, which remain elusive at the…
In a supersymmetric extension of the Standard Model of particle physics (SM) with low scale of supersymmetry breaking, sgoldstino of (sub)TeV mass can be observed at the Large Hadron Collider (LHC) as a peak in diboson mass spectra. Moreover, as a singlet with respect to the SM gauge group, scalar sgoldstino can mix with the SM-like Higgs boson and interfere in all neutral channels providing with the promising signatures of new physics if superpartners are heavy. Sgoldstino couplings to the SM particles are determined by the pattern of soft supersymmetry breaking parameters. Here we concentrat…
The electroweak symmetry breaking (EWSB) mechanism is still an undecided question in particle physics. We propose to utilize the single top quark and Higgs associated production ($th$), $Zh$ production via gluon fusion at the LHC to probe the couplings between the Higgs and the gauge bosons and further to test the EWSB. We demonstrate that the $th$ and $gg\to Zh$ productions are sensitive to the relative sign of couplings ($ht\bar{t}$, $hWW$) and ($ht\bar{t}$, $hZZ$), respectively. We find that the relative sign between $hWW$ and $hZZ$ couplings could be fully determined after combining the pr…