Search

The $W$ boson mass is one of the most important electroweak precision observables for testing the Standard Model or its extensions. The very recent measured $W$ boson mass at CDF shows about $7\sigma$ deviations from the SM prediction, which may challenge the internal consistency of the SM. By performing the global electroweak fit with the new $W$-boson, we present the new values of the oblique parameters: $S = 0.06 \pm 0.10$, $T= 0.11 \pm 0.12$, $U=0.13 \pm 0.09$, or $S=0.14 \pm 0.08$, $T= 0.26 \pm 0.06$ with $U =0$ and the corresponding correlation matrices, which strongly indicates the need for the non-degenerate multiplets beyond the SM. As a proof-of-concept, we show that the new results can be accommodated in the two-Higgs doublet model, where the charged Higgs boson has to be either heavier or lighter than both two heavy neutral Higgs bosons. Therefore, searching for these non-SM Higgs bosons will provide a complementary way to test the new physics for the $W$ boson mass anomaly., Comment: two columns, 10 pages, 8 figures

In the type-I two-Higgs-doublet model, existing theoretical and experimental constraints still permit the light charged Higgs boson with a mass below the top quark mass. We present a complete roadmap for the light charged Higgs boson at the LHC through the comprehensive phenomenology study, focusing on the normal scenario where the lighter \textit{CP}-even Higgs boson is the observed Higgs boson. In type-I, it is challenging to simultaneously accommodate the light mass of the charged Higgs boson and the constraints from theory, electroweak precision data, Higgs data, $b\to s \gamma$, and direct search bounds. Consequently, the parameter space is extremely curtailed, which predicts somewhat definite phenomenological signatures. We find that the mass of the pseudoscalar Higgs boson, $M_A$, is the most crucial factor in the phenomenology of the charged Higgs boson. If $M_A$ is light, the charged Higgs boson decays mainly into $A W^\pm$. When $M_A$ is above the $A W^\pm$ threshold, the dominant decay mode is into $ \tau^\pm \nu$. Over the whole viable parameter space, we study all the possible production and decay modes of charged Higgs bosons at the LHC, and suggest three efficient channels: (i) $pp \to H^+ H^-\to [\tau \nu] [\tau \nu]$; (ii) $pp \to HA/HH/AA \to H^\pm W^\mp H^\pm W^\mp \to [\tau \nu] [\tau \nu] W W$; (iii) $pp \to H^+ H^-\to [b \bar b W ] [b \bar b W ] $. Based on the sophisticated signal-background analyses including detector simulation, we showed that the significance of the first final state is large, that of the second one is marginal around three, but the third one suffers from huge $t\bar t$ related backgrounds., Comment: The final version to appear in PRD

The 2→3 scattering of longitudinal vector bosons (VBS) has been proven to be a complementary channel to measure the Higgs self-couplings in the Standard Model (SM) and the SM effective field theory (SMEFT) at colliders. We perform the first comprehensive study of all main 2→3 VBS processes at high-energy muon colliders, especially including background analysis. The main contributing channels turn out to be the scattering of W+W−→W+W−h, ZZh, and hhh. We obtain the constraints on c6 and cΦ1 which are the Wilson coefficients of the dimension-6 operators relevant for Higgs self-couplings in the SMEFT. With the center-of-mass energies of 10 TeV and 30 TeV, we find the expected sensitivity to the coefficients c6/Λ2 and cΦ1/Λ2 can reach the level of 0.01 TeV−2. The tightest constraints come from the hhh channel, while the constraints from WWh are also comparable. Our results crucially depend on selecting the longitudinal polarizations for the final W and Z bosons. We then study how the sensitivities change by varying the efficiency of tagging longitudinal polarizations, and find that the significance remains consistently high.

We perform a comprehensive analysis for the light scalar dark matter (DM)in the Inert two Higgs doublet model (i2HDM) with compressed mass spectra, small mass splittings among three $\mathbb{Z}_2$ odd particles---scalar $S$, pseudo-scalar $A$, and charged Higgs $H^\pm$. In such a case, the co-annihilation processes play a significant role to reduce DM relic density. As long as a co-annihilation governs the total interaction rate in the early universe, a small annihilation rate is expected to reach a correct DM relic density and its coupling $\lambda_S$ between DM pair and Higgs boson shall be tiny. Consequently, a negligible DM-nucleon elastic scattering cross section is predicted at the tree-level. In this work, we include the one-loop quantum corrections of the DM-nucleon elastic scattering cross section. We found that the quartic self-coupling $\lambda_2$ between $\mathbb{Z}_2$ odd particles indeed contributes to the one-loop quantum correction and behaves non-trivially for the co-annihilation scenario. Interestingly, the parameter space, which is allowed by the current constraints considered in this study, can predict the DM mass and annihilation cross section at the present compatible with the AMS-02 antiproton excess. The parameter space can be further probed at the future high luminosity LHC., Comment: 41 pages, JHEP accepted version

Recently, Altmannshofer, Dror and Gori (2022) claimed there is a four-point interaction, $W$-$\ell$-$\nu$-$a$, in electroweak-violating scenario of axion-like particle (ALP) and lepton interactions which plays a critical role in searching for ALPs from $\pi^{\pm}$, $K^{\pm}$ mesons and $W$ boson decays because of the novel energy enhancements. Inspired by this interesting finding, we first propose new t-channel processes, $e^{+}e^{-}\rightarrow\nu_e a\bar{\nu_e}$ and $e^{-}p\rightarrow\nu_e a j$, for electrophilic ALPs ($e$ALPs) which also involve $W$-$\ell$-$\nu$-$a$ four-point interaction and have obvious energy enhancement behaviors in their cross sections when the collision energy is increasing. On the other hand, heavier $e$ALPs mainly decay to a photon pair induced by the chiral anomaly instead of an electron-positron pair. Therefore, studies of these t-channel processes with a photon pair plus missing energy at $e^+ e^-$ and $ep$ colliders open a new door to search for $e$ALPs at high energy colliders. The proposed search strategies are not only aiming to generate a larger production rate of ALPs, but also trying to distinguish electroweak-violating ALP-lepton interactions from electroweak-preserving ones., Comment: 16 pages, 12 figures, 5 tables. Comments are welcome

Many extensions of the standard model (SM) predict the existence of axion-like particles and/or dark Higgs in the sub-GeV scale. Two new sub-GeV particles, a scalar and a pseudoscalar, produced through the Higgs boson exotic decays, are investigated. The decay signatures of these two new particles with highly collimated photons in the final states are discriminated from the ones of SM backgrounds using the Convolutional Neural Networks and Boosted Decision Trees techniques. The sensitivities of searching for such new physics signatures at the Large Hadron Collider are obtained.

In this work, we reanalyze the multi-component strongly interacting massive particle (mSIMP) scenario using an effective operator approach. As in the single-component SIMP case, the total relic abundance of mSIMP dark matter (DM) is determined by the coupling strengths of $3 \to 2$ processes achieved by a five-point effective operator. Intriguingly, we notice that there is an irreducible $2 \to 2$ process induced by the corresponding five-point interaction in the dark sector, which would reshuffle the mass densities of SIMP DM after the chemical freeze-out. We dub this DM scenario as reshuffled SIMP ($r$SIMP). Given this observation, we then numerically solve the coupled Boltzmann equations including the $3 \to 2$ and $2 \to 2$ processes to get the correct yields of $r$SIMP DM. It turns out that the masses of $r$SIMP DM must be nearly degenerate for them to contribute sizable abundances. On the other hand, we also introduce effective operators to bridge the dark sector and visible sector via a vector portal coupling. Notably, we find that the reshuffled mechanism in the $r$SIMP scenario is sensitive to the size of the DM self-interacting cross section., Comment: 8 pages, 3 figures, 3 tables, the title changed. Matches the version published in Phys.Dark Univ

Recently, we have witnessed two hints of physics beyond the standard model: A 3.3$\sigma$ local excess ($M_{A_0} = 52$ GeV) in the search for $H_0\to A_0 A_0\to b\bar{b}\mu^{+}\mu^{-}$ and a 4.2$\sigma$ deviation from the SM prediction in the $(g-2)_\mu$ measurement. The first excess was found by the ATLAS Collaboration using 139 fb$^{-1}$ data at $\sqrt{s}=13$ TeV. The second deviation is a combination of the results from the Brookhaven E821 and the recently reported Fermilab E989 experiment. We attempt to explain these deviations in terms of a renormalizable simplified dark matter model. Inspired by the null signal result from dark matter (DM) direct detection, we interpret the possible new particle, $A_0$, as a pseudoscalar mediator connecting DM and the standard model. On the other hand, a new vector-like muon lepton can explain these two excesses at the same time while contributiong to the DM phenomenology., Comment: 28 pages, 8 figures. Recasting of SR5L added and figures updated accordingly. More references added. v3: Matches published version

The inelastic dark matter model is one kind of popular models for the light dark matter (DM) below $O(1)$ GeV. If the mass splitting between DM excited and ground states is small enough, the co-annihilation becomes the dominant channel for thermal relic density and the DM excited state can be long-lived at the collider scale. We study scalar and fermion inelastic dark matter models for $ {\cal O}(1) $ GeV DM at Belle II with $ U(1)_D $ dark gauge symmetry broken into its $Z_2$ subgroup. We focus on dilepton displaced vertex signatures from decays of the DM excited state. With the help of precise displaced vertex detection ability at Belle II, we can explore the DM spin, mass and mass splitting between DM excited and ground states. Especially, we show scalar and fermion DM candidates can be discriminated and the mass and mass splitting of DM sector can be determined within the percentage of deviation for some benchmark points. Furthermore, the allowed parameter space to explain the excess of muon $(g-2)_\mu$ is also studied and it can be covered in our displaced vertex analysis during the early stage of Belle II experiment., Comment: 42 pages, 13 figures, and 5 tables, version published in JHEP

Same-sign charged Higgs pair production via vector-boson scattering is a useful probe of the mass spectrum among the heavier scalar, pseudoscalar, and charged Higgs bosons in two-Higgs-doublet models. It has been shown that the production cross section scales as the square of the mass difference $\Delta m = (m_{H^0} - m_{A^0})$ in the alignment limit $(\cos(\beta - \alpha)=0)$. We study the potential measurement of this same-sign charged Higgs pair production at the high-luminosity LHC (HL-LHC) and the proposed 27 TeV $pp$ collider, with emphasis in the decay channel $H^\pm H^\pm \to (W^\pm A^0 ) (W^\pm A^0)$, which is in general the dominant mode when the charged Higgs mass is above the $W^\pm A^0$ threshold. We also examine the current allowed parameter space taking into account the theoretical constraints on the model, the electroweak precision measurements, $B$ decays, and direct searches in the $H^\pm \to \tau^\pm \nu_\tau$ and $H^\pm \to W ^\pm A^0 \to (\ell^\pm\nu_{\ell} ) (\mu \mu)$., Comment: Published version

The model of heavy neutral leptons (HNLs) is one of the well-motivated models beyond the standard model from both theoretical and phenomenological point of views. It is an indispensable ingredient to explain the puzzle of tiny neutrino masses and the origin of the matter-antimatter asymmetry in our Universe, based on the models in which the simplest type-I seesaw mechanism can be embedded. The HNL with a mass up to the electroweak scale is an attractive scenario which can be readily tested in present or near-future experiments including the LHC. In this work, we study the decay rates of HNLs and find the sensitive parameter space of the mixing angles between the active neutrinos and HNLs. Since there are fewer collider studies of the mixing between ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ and HNL in literature compared with those of ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ for the HNL of mass in the electroweak scale, we focus on the channel $pp\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}(*)}+X\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}}N+X$ to search for HNLs at the LHC 14 TeV. The targeted signature consists of three prompt charged leptons, which include at least two tau leptons. After the signal-background analysis, we further set sensitivity bounds on the mixing $|{U}_{\ensuremath{\tau}N}{|}^{2}$ with ${M}_{N}$ at high-luminosity LHC (HL-LHC). We predict the testable bounds from HL-LHC can be stronger than the previous LEP constraints and electroweak precision data (EWPD), especially for ${M}_{N}\ensuremath{\lesssim}50\text{ }\text{ }\mathrm{GeV}$ can reach down to $|{U}_{\ensuremath{\tau}N}{|}^{2}\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$.

There are two kinds of new physics effects on non-resonant di-Higgs process from gluon fusion, non-SM Higgs trilinear self-coupling $\lambda_{hhh}$ or new colored particles running in the loop. With the aim of disentangling different new physics contributions, we study their characteristics in the kinematic distributions. Assuming that the total cross section is observed to be about three times as large as the SM expectation, we consider the cases of $\lambda_{hhh}/\lambda_{hhh}^{\rm SM} =-0.5, 5.5$ as well as a new physics model with heavy vectorlike quarks in a type-II two Higgs double model, called the VLQ-2HDM. A reasonable benchmark point is suggested in the exact wrong-sign limit, where the opposite sign between the up-type VLQ and down-type VLQ couplings to the Higgs boson causes the cancellation of their contributions to the single-Higgs production from gluon fusion. Because of the threshold effects from the heavy VLQs in the loop, the VLQ-2HDM accommodates the bumps in the distributions of the invariant mass of the Higgs boson pair ($M_{hh}$) and the transverse momentum of a Higgs boson ($p_T^h$). The positions of two bumps are closely related as $ M_{hh} \simeq 2 M_{\rm VLQ}$ and $p_T^h \simeq M_{\rm VLQ}$. In addition, the bumps located at the heavy VLQ mass naturally lift up the $M_{hh}$ and $p_T^h$ distributions into high-mass and high-$p_T^h$ regions. On the other hand, the non-SM Higgs trilinear coupling cases have the distributions shift into low $ M_{hh}$ and $p_T^h$ regions. Therefore, the kinematic region with high $M_{hh}$ and high $p_T^h$ will be a smoking-gun signal for the VLQ-2HDM. Full HL-LHC simulations for the di-Higgs signals are also performed, confirming that the $b \bar{b} b \bar{b}$ final state can distinguish the VLQ-2HDM., Comment: References are added: 29 pages with 8 figures

In this paper we study sneutrino dark matter in a recently proposed supersymmetric electroweak-scale inverse seesaw model, in which the majority of the sneutrino dark matter particle is a mixture of the right-handed sneutrino $\tilde{N}^c$ and the singlet field $\tilde{S}$. The scalar field $X$ responsible for the generation of neutrino masses can simultaneously play a crucial role for sneutrino annihilation in the early Universe via the pseudoscalar mediator $A_X$ into neutrinos. We focus here on the dominant annihilation channels and provide all the formulas together with analytic estimates in order to identify the relevant parameters. Furthermore, we show that the direct detection scattering cross section is many orders of magnitude below the current limits, and estimate the indirect detection annihilation rate, which is only a few orders of magnitude below the current limits., Comment: 24 pages, 8 figures, and 2 tables. https://sarah.hepforge.org/trac/wiki/inverse-Seesaw-SUSY-EW, v2: correspond to published version

Motivated by a local $3.2-3.4$ sigma resonance in $WH$ and $ZH$ in the ATLAS Run 2 data, we attempt to interpret the excess in terms of a $W'$ boson in a $SU(2)_1 \times SU(2)_2 \times U(1)_X$ model. We stretch the deviation from the alignment limit of the Equivalence Theorem, so as to maximize $WH$ production while keeping the $WZ$ production rate below the experimental limit. We found a viable though small region of parameter space that satisfies all existing constraints on $W' \to jj, t \bar b, WZ$, as well as the precision Higgs data. The cross section of $W' \to WH$ that we obtain is about $5-6$ fb., 14 pages, 2 figures

We perform the most up-to-date comprehensive signal-background analysis for Higgs-pair production in $HH\ensuremath{\rightarrow}b\overline{b}\ensuremath{\gamma}\ensuremath{\gamma}$ channel at the HL-LHC and HL-100 TeV hadron collider, with the goal of probing the self-coupling ${\ensuremath{\lambda}}_{3H}$ of the Higgs boson which is normalized to its standard-model value of 1. We simulate all the standard-model signal and background processes and emphasize that the $ggH(\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})$ background has been overlooked in previous studies. We find that, even for the most promising channel $HH\ensuremath{\rightarrow}b\overline{b}\ensuremath{\gamma}\ensuremath{\gamma}$ at the HL-LHC with a luminosity of $3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, the significance is still not high enough to establish the Higgs self-coupling at the standard-model (SM) value. Instead, we can only constrain the self-coupling to $\ensuremath{-}1.0l{\ensuremath{\lambda}}_{3H}l7.6$ at 95% confidence level after considering the uncertainties associated with the top-Yukawa coupling and the estimation of backgrounds. Here we also extend the study to the HL-100 TeV hadron collider. With a luminosity of $3\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$, we find there exists a bulk region of $2.6\ensuremath{\lesssim}{\ensuremath{\lambda}}_{3H}\ensuremath{\lesssim}4.8$ in which one cannot pin down the trilinear coupling. Otherwise, one can measure the coupling with a high precision. At the SM value, for example, we show that the coupling can be measured with about 20% accuracy. While assuming $30\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$, the bulk region reduces to $3.1\ensuremath{\lesssim}{\ensuremath{\lambda}}_{3H}\ensuremath{\lesssim}4.3$, and the trilinear coupling can be measured with about 7% accuracy at the SM value.

We present the MadAnalysis 5 implementation and validation of the ATLAS-SUSY-2018-04 search. This ATLAS analysis targets direct stau production in events with two hadronic tau leptons, and probes 139 fb[Formula: see text] of LHC proton–proton collisions at a center-of-mass energy of 13 TeV. The validation of our re-implementation relies on a comparison of our cutflow predictions with the auxiliary material and official results provided by the ATLAS collaboration in the context of two supersymmetry-inspired simplified benchmark models in which the Standard Model is extended by a neutralino and a stau decaying into a tau lepton and a neutralino. A first scenario focuses on very light staus, whereas a second one addresses heavier staus. Our predictions have been found to agree with ATLAS official cutflows at the level of 6–8% in the heavy stau scenario, and exhibit a larger discrepancy (of 15–50%) in the light stau scenario. This disagreement is however considered as not too significant, as both ATLAS and MadAnalysis 5 predictions come with large Monte Carlo numerical uncertainties.

Recently a gauged two Higgs doublet model, in which the two Higgs doublets are embedded into the fundamental representation of an extra local $SU(2)_H$ group, is constructed. Both the new gauge bosons $Z^\prime$ and $W^{\prime (p,m)}$ are electrically neutral. While $Z^\prime$ can be singly produced at colliders, $W^{\prime (p,m)}$, which is heavier, must be pair produced. We explore the constraints of $Z^\prime$ using the current Drell-Yan type data from the Large Hadron Collider. Anticipating optimistically that $Z^\prime$ can be discovered via the clean Drell-Yan type signals at high luminosity upgrade of the collider, we explore the detectability of extra heavy fermions in the model via the two leptons/jets plus missing transverse energy signals from the exotic decay modes of $Z^\prime$. For the $W^{\prime (p,m)}$ pair production in a future 100 TeV proton-proton collider, we demonstrate certain kinematical distributions for the two/four leptons plus missing energy signals have distinguishable features from the Standard Model background. In addition, comparisons of these kinematical distributions between the gauged two Higgs doublet model and the littlest Higgs model with T-parity, the latter of which can give rise to the same signals with competitive if not larger cross sections, are also presented., 39 pages, 23 figures, 7 tables and two new appendixes, to appear in EPJC

Suppose a heavy neutral Higgs or scalar boson H is discovered at the LHC, it is important to investigate its couplings to the standard model particles as much as possible. Here in this work we attempt to probe the CP-even and CP-odd couplings of the heavy Higgs boson to a pair of top quarks, through the decay $$ H\to t\overline{t}\to b{W}^{+}\overline{b}{W}^{-} $$ H → t t ¯ → b W + b ¯ W − . We use the helicity-amplitude method to write down the most general form for the angular distributions of the final-state b quarks and W bosons. We figure out that there are 6 types of angular observables and, under $$ \mathrm{C}\mathrm{P}\tilde{\mathrm{T}} $$ C P T ˜ conservation, one-dimensional angular distributions can only reveal two of them. Nevertheless, the H couplings to the $$ t\overline{t} $$ t t ¯ pair can be fully determined by exploiting the one-dimensional angular distributions. A Higgs-boson mass of 380 GeV not too far above the $$ t\overline{t} $$ t t ¯ threshold is illustrated with full details. With a total of 104 events of $$ H\to t\overline{t}\to b{W}^{+}\overline{b}{W}^{+} $$ H → t t ¯ → b W + b ¯ W + , one can determine the couplings up to 10-20% uncertainties.

In this paper we propose a novel supersymmetric inverse seesaw model which has only one additional $Z_6$ symmetry. The field content is minimal to get a viable neutrino spectrum at tree-level. Interestingly, the inverse seesaw scale in our model is related to the scale of electroweak symmetry breaking. Due to that origin we are less biased about hierarchies and discuss three different types of the inverse seesaw mechanism with different phenomenologies. We can successfully reproduce neutrino masses and mixing and our model is consistent with current bounds on neutrinoless double beta decay, non-unitarity of the PMNS matrix and charged lepton flavor violation., Comment: 20 pages, 1 figure; version published in JHEP

A muon jet ($\mu$-jet) is a very special feature that consists of a cluster of collimated muons from the decay of a fast moving light particle of mass about $\mathcal{O}$(1 GeV). We will use this feature to search for very light particles from rare decays of the Higgs boson. For such a small angular separation of muons which might come from a long-lived particle, both ATLAS and CMS could have the displaced-vertexing-reconstruction capability. We use two simple models of the Higgs-portal type to explore the possibilities of event topologies with two $2\mu$-jets, one $2\mu$-jet $\&$ one $4\mu$-jet, and two $4\mu$-jets in the final state at LHC-14. We also summarize existing constraints on these models., Comment: v3: 38 pages, 16 figures, accepted version by PRD

We study the associated production of a charged Higgs boson with a bottom quark and a light quark at the LHC via p p \to H^\pm\,b\,j in the Two Higgs Doublet Models (2HDMs). Using the effective W approximation, we show that there is exact cancellation among various Feynman diagrams in high energy limit. This may imply that the production of charged Higgs can be significantly enhanced in the presence of large mass differences among the neutral Higgs bosons via W^\pm-Higgs fusion in the p p \to H^\pm\,b\,j process. Particularly, we emphasize the potential enhancement due to a light pseudoscalar boson $A$, which is still allowed by the current data by which we explicitly calculate the allowed regions in (M_A,\,\tan\beta) plane, and show that the production cross section can be as large as 0.1 pb for large $\tan\beta$. We also show that the transverse momentum distribution of the b quark can potentially distinguish the W^\pm-A fusion diagram from the top diagram. Finally, we point out further enhancement when we go beyond the 2HDMs., Comment: 25 pages, 9 pdf figures, Matches the published JHEP version

Higgs-boson pair production is well known being capable to probe the trilinear self-coupling of the Higgs boson, which is one of the important ingredients of the Higgs sector itself. Pair production then depends on the top-quark Yukawa coupling $g_t^{S,P}$, Higgs trilinear coupling $\lambda_{3H}$, and a possible dim-5 contact-type $ttHH$ coupling $g_{tt}^{S,P}$, which may appear in some higher representations of the Higgs sector. We take into account the possibility that the top-Yukawa and the $ttHH$ couplings involved can be CP violating. We calculate the cross sections and the interference terms as coefficients of the square or the 4th power of each coupling $(g_t^{S,P}, \lambda_{3H}, g_{tt}^{S,P})$ at various stages of cuts, such that the desired cross section under various cuts can be obtained by simply inputing the couplings. We employ the $H H \to \gamma\gamma b \bar b$ decay mode of the Higgs-boson pair to investigate the possibility of disentangle the triangle diagram from the box digram so as to have a clean probe of the trilinear coupling at the LHC. We found that the angular separation between the $b$ and $\bar b$ and that between the two photons is useful. We obtain the sensitivity reach of each pair of couplings at the 14 TeV LHC and the future 100 TeV pp machine. Finally, we also comment on using the $b\bar b \tau^+ \tau^-$ decay mode in Appendix., Comment: v3: 50 pages, 24 figures: 1 new CPV scenario and 3 new figures are added; v4: published version, title changed in the journal version

Motivated by the di-photon resonance recently reported by the ATLAS and CMS collaborations at $\sqrt{s} =13$ TeV, we interpret the resonance as a scalar boson $X (750)$ in hidden-valley-like models. The scalar boson $X$ can mix with the standard model Higgs boson and thus can be produced via gluon fusion. It then decays into a pair of very light hidden particles $Y$ of sub-GeV, each of which in turn decays to a pair of collimated $ \pi^{0} $'s, and these two $ \pi^{0} $'s decay into photons which then form photon-jets. A photon-jet ($ \gamma $-jet) is a special feature that consists of a cluster of collinear photons from the decay of a fast moving light particle (sub-GeV). Because these photons inside the photon-jet are so collimated that it cannot be distinguished from a single photon, and so in the final state of the decay of $X(750)$ a pair of photon-jets look like a pair of single photons, which the experimentalists observed and formed the 750 GeV di-photon resonance. Prospects for the LHC Run-2 about other new and testable features are also discussed., Comment: v2: 23 pages, 7 figures, more discussion on constraints of X and Y bosons, accepted version by PRD; v1: 19 pages, 7 figures

Associated production of the Higgs boson with a single top quark proceeds through Feynman diagrams, which are either proportional to the hWW, top-Yukawa, or the bottom-Yukawa couplings. It was shown in literature that the interference between the top-Yukawa and the gauge-Higgs diagrams can be significant, and thus the measurement of the cross sections can help pin down the sign and the size of the top-Yukawa coupling. Here we perform a detailed study with full detector simulations of such a possibility at the LHC-14 within the current allowed range of hWW and top-Yukawa couplings, using h-> b b-bar, \gamma\gamma, \tau+ \tau-, ZZ* -> 4 l modes. We found that the LHC-14 has the potential to distinguish the size and the sign of the top-Yukawa coupling. Among the channels the h-> b b-bar mode mode provides the best chance to probe the signal, followed by the h -> \gamma\gamma\ mode, which has the advantage of a narrow reconstructed mass peak. We also pointed out that the spatial separation among the final-state particles has the potential in differentiating among various values of the top-Yukawa coupling., Comment: 28 pages, 13 figures; a comment about NLO correction is added, references added; match the published version

More evidences have now been collected at the Large Hadron Collider suggesting the new 125 - 126 GeV boson is likely the long sought Higgs boson in the standard model. One pressing question continued being asked by theorists is whether this Higgs boson is a lone player responsible for the full electroweak symmetry breaking. Current data still allow room for additional Higgs bosons or some other UV physics that may play a partial role in electroweak symmetry breaking as well. We use the WW scattering to investigate such a possibility, using the two-Higgs-doublet model as a prototype. The WW scattering becomes strong when the extra Higgs bosons are very heavy. We study the sensitivity of the partially strong WW scattering signals at the 13 TeV Large Hadron Collider.

Motivated by the excess in the diphoton production rate of the Higgs boson at the Large Hadron Collider (LHC), we investigate the possibility that one of the $CP$-even Higgs bosons of the extra $U(1)$ extended minimal supersymmetric standard model can give a consistent result. We scan the parameter space for a standard-model-like Higgs boson such that the mass is in the range of 124--127 GeV and the production rate $\ensuremath{\sigma}B$ of the $W{W}^{*}$, $Z{Z}^{*}$ modes is consistent with the standard model (SM) values, while that of $\ensuremath{\gamma}\ensuremath{\gamma}$ is enhanced relative to the SM value. We find that the SM-like Higgs boson is mostly the lightest $CP$-even Higgs boson and it has a strong mixing with the second lightest one, which is largely singletlike. The implications on $Z\ensuremath{\gamma}$ production rate and properties of the other Higgs bosons are also studied.

The recent observation of three events by the CDMS II experiment can be interpreted as a 8.6 GeV dark matter scatters elastically with the nucleons inside the silicon detectors with a spin-independent cross section of 1.9 x 10^-41 cm^2. We employ the effective dark matter interaction approach to fit to the interpreted cross section, and make predictions for monojet and monophoton production at the LHC with the fitted parameters. We show that some of the operators are already ruled out by current data while the others can be further probed in the upcoming 14 TeV run of the LHC., Comment: 13 pages. arXiv admin note: text overlap with arXiv:1201.3402