Upgrading Sterile Neutrino Dark Matter to FImmP Using Scale Invariance

In this article we propose a class of extremely light feebly interacting massive particle, FI$m$Ps. They are combination of feebly interacting massive particle with scale invariance, by which DM stability, mass origin and relic density are inherently related. In the scale invariant version of the Standard Model (SM) with three right-handed neutrinos ($\nu$SISM), the lightest $N_1$ realizes the FI$m$P scenario. In this example scalar singlets, which are intrinsic to the $\nu$SISM, generate mass and relic density for this FI$m$P simultaneously. Moreover, they are badly needed for electroweak symmetry spontaneously breaking. Interestingly, a 7.1 keV $N_1$ with correct relic density, that can explain the recent 3.55 keV $X-$ray line, lies in the bulk parameter space of our model.Comment: journal version; title changed and presentation adjusted accordingly; 24 page

Bound States via Higgs Exchanging and Resonant Di-Higgs

The standard model (SM)-like Higgs boson $h$ has spin zero and light mass around weak scale, so it has the potential to mediate a new and relatively strong force for the particle $\phi$ in the new physics (NP) sector; then $\phi$ may form bound state $B_h$ via exchanging $h$. This phenomena may arise in a wide context, for instance composite Higgs, supersymmetry (SUSY) and radiative neutrino (or more widely in the models with a strong Higgs portal for triggering classical scale symmetry breaking or strong first-order phase transition). For illustration we focus on two typical examples, the stop/sbottom sector and an inert Higgs doublet. Furthermore, we point out that $B_h$ must give rise to a clear resonant di-Higgs signature, which recently has been extensively searched for at the large hadron collider (LHC). Moreover, Higgs radiative decay such as to di-photon probably will be significantly modified provided that $\phi$ is charged or/and colored.Comment: PLB version with minor correction

New Physics Opportunities in the Boosted Di-Higgs plus \ET Signature

The Higgs field in the standard model (SM) may couple to new physics sectors related with dark matter and/or massive neutrinos. In this paper we propose a novel signature, the boosted di-Higgs boson plus \ET (which is either a dark matter or neutrino), to probe those new physics sectors. In a large class of models, in particular the supersymmetric SMs and low scale seesaw mechanisms, this signature can play a key role. The signature has clear background, and at the $\sqrt s=$14 TeV high luminosity (HL-)LHC, we can probe it with production rate as low as $\sim$ 0.1 fb. We apply it to benchmark models, supersymmetry in the bino-Higgsino limit, the canonical seesaw model and little Higgs model, finding that masses of Higgsino, right-handed neutrino and heavy vector boson can be probed up to $\sim$ 500 GeV, 650 GeV and 900 GeV, respectively.Comment: Version to appear in PRL; major revision according to the referees' suggestion. The supplement file will be available from the e-journa

Highlights of Supersymmetric Hypercharge ±1\pm1 Triplets

The discovery of a standard model (SM)-like Higgs boson with a relatively heavy mass $m_h$ and hints of di-photon excess has deep implication to supersymmetric standard models (SSMs). We consider the SSM extended with hypercharge $\pm1$ triplets, and investigate two scenarios of it: (A) Triplets significantly couple to the Higgs doublets, which can substantially raise $m_h$ and simultaneously enhance the Higgs to di-photon rate via light chargino loops; (B) Oppositely, these couplings are quite weak and thus $m_h$ can not be raised. But the doubly-charged Higgs bosons, owing to the gauge group structure, naturally interprets why there is an excess rather than a deficient of Higgs to di-photon rate. Additionally, the pseudo Dirac triplet fermion is an inelastic non-thermal dark matter candidate. Light doubly-charged particles, especially the doubly-charged Higgs boson around 100 GeV in scenario B, are predicted. We give a preliminary discussion on their search at the LHC.Comment: JHEP version. Typos fixed, comments, references and acknowledge adde

Strong First Order EWPT and Strong Gravitational Waves in Z3Z_3-symmetric Singlet Scalar Extension

The nature of electroweak (EW) phase transition (PT) is of great importance. It may give a clue to the origin of baryon asymmetry if EWPT is strong first order. Although it is second order within the standard model (SM), a great many extensions of the SM are capable of altering the nature. Thus, gravitational wave (GW), which is supposed to be relics of strong first order PT, is a good complementary probe to new physics beyond SM (BSM). We in this paper elaborate the patterns of strong first order EWPT in the next to simplest extension to the SM Higgs sector, by introducing a $Z_3$-symmetric singlet scalar. We find that, in the $Z_3$-symmetric limit, the tree level barrier could lead to strong first order EWPT either via three or two-step PT. Moreover, they could produce two sources of GW, despite of the undetectability from the first-step strong first order PT for the near future GW experiments. But the other source with significant supercooling which then gives rise to $\alpha\sim{\cal O}(0.1)$ almost can be wholly covered by future space-based GW interferometers such as eLISA, DECIGO and BBO.Comment: references adde

The Nelson-Seiberg theorem revised

The well-accepted Nelson-Seiberg theorem relates R-symmetries to supersymmetry (SUSY) breaking vacua, and provides a guideline for SUSY model building which is the most promising physics beyond the Standard Model. In the case of Wess-Zumino models with perturbative superpotentials, we revise the theorem to a combined necessary and sufficient condition for SUSY breaking which can be easily checked before solving the vacuum. The revised theorem provides a powerful tool to construct either SUSY breaking or SUSY vacua, and offers many practicable applications in low energy SUSY model building and string phenomenology.Comment: 5 pages; v2: abstract and introduction revised; v3: condition of perturbative superpotentials added, JHEP published versio

Uncover Compressed Supersymmetry via Boosted Bosons from the Heavier Stop/Sbottom

A light stop around the weak scale is a hopeful messenger of natural supersymmetry (SUSY), but it has not shown up at the current stage of LHC. Such a situation raises the question of the fate of natural SUSY. Actually, a relatively light stop can easily be hidden in a compressed spectra such as mild mass degeneracy between stop and neutralino plus top quark. Searching for such a stop at the LHC is a challenge. On the other hand, in terms of the argument of natural SUSY, other members in the stop sector, including a heavier stop $\tilde{t}_2$ and lighter sbottom $\tilde{b}_1$ (both assumed to be left-handed-like), are also supposed to be relatively light and therefore searching for them would provide an alternative method to probe natural SUSY with a compressed spectrum. In this paper we consider quasi-natural SUSY which tolerates relatively heavy colored partners near the TeV scale, with a moderately large mass gap between the heavier members and the lightest stop. Then $W/Z/h$ as companions of $\tilde{t}_2$ and $\tilde{b}_1$ decaying into $\tilde{t}_1$ generically are well boosted, and they, along with other visible particles from $\tilde{t}_1$ decay, are a good probe to study compressed SUSY. We find that the resulting search strategy with boosted bosons can have better sensitivity than those utilizing multi-leptons.Comment: 19 pages, 6 figures, to appear in EPJ

New Avenues to Heavy Right-handed Neutrinos with Pair Production at Hadronic Colliders

In many models incorporating the type-I seesaw mechanism, the right-handed neutrino ($N$) couples to heavy vector/scalar bosons and thereby has resonant pair production. It barely receives attention thus far, however, it may provide the best avenue to probe TeV scale $N$ without requiring anomalously large mixing between $N$ and the active neutrino $\nu_L$. In this paper we explore the discovery prospects of (mainly heavy) $N$ pair production at the 14 TeV LHC and future 100 TeV $pp$ collider, based on the three signatures: 1) trilepton from $N(\rightarrow \ell W_\ell)N(\rightarrow \ell W_h)$ with $W_{\ell/h}$ the leptonically/hadronically decaying $W$; 2) boosted di-Higgs boson plus MET from $N(\rightarrow \nu_L h)N(\rightarrow \nu_L h)$; 3) a single boosted Higgs with leptons and MET from $N(\rightarrow \ell W_\ell)N(\rightarrow \nu_L h)$. At the 100 TeV collider, we also consider the situation when the Higgs boson is over boosted thus losing its jet substructure. Interpreting our tentative results in the benchmark model, the local $B-L$ model, we find that the (multi-) TeV scale $N$ can be probed at the (100) 14 TeV colliders.Comment: 34 pages, 8 figures, version to be published in Phys. Rev.