Search

If fermionic dark matter (DM) is stabilized by dark U(1) gauge symmetry that is spontaneously broken into its subgroup Z2, the particle contents of the model becomes very rich: DM and excited DM, both of them are Majorana fermions, as well as two dark force mediators, dark photon and dark Higgs boson are naturally present due to the underlying dark gauge symmetry. In this paper, we study the DM bound state formation processes within this scenario, assuming both dark photon and dark Higgs are light mediators and including the effects of excited DM. The Goldstone boson contributions to the potential matrix in the Schrödinger equations are found to be important. The emissions of a longitudinal vector boson (or somehow equivalently a Goldstone boson) during the DM bound state formations are crucial to induce a significant reannihilation process, reducing the dark matter relic abundance. Most of the stringent constraints for this kind of dark matter considered in the literature are simply evaded.

Multi-component dark matter scenarios are studied in the model with U(1)X dark gauge symmetry that is broken into its product subgroup Z2 × Z3 á la Krauss-Wilczek mechanism. In this setup, there exist two types of dark matter fields, X and Y, distinguished by different Z2 × Z3 charges. The real and imaginary parts of the Z2-charged field, XR and XI, get different masses from the U(1)X symmetry breaking. The field Y, which is another dark matter candidate due to the unbroken Z3 symmetry, belongs to the Strongly Interacting Massive Particle (SIMP)-type dark matter. Both XI and XR may contribute to Y’s 3 → 2 annihilation processes, opening a new class of SIMP models with a local dark gauge symmetry. Depending on the mass difference between XI and XR, we have either two-component or three-component dark matter scenarios. In particular two- or three-component SIMP scenarios can be realised not only for small mass difference between X and Y, but also for large mass hierarchy between them, which is a new and unique feature of the present model. We consider both theoretical and experimental constraints, and present four case studies of the multi-component dark matter scenarios.

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

We investigate a model of dark sector based on non-Abelian $SU(2{)}_{D}$ gauge symmetry. This dark gauge symmetry is broken into discrete ${Z}_{2}$ via vacuum expectation values of two real triplet scalars, and an $SU(2{)}_{D}$ doublet Dirac fermion becomes ${Z}_{2}$---odd particles whose lighter component makes stable dark matter candidate. The standard model and dark sector can be connected via the scalar mixing and the gauge kinetic mixing generated by higher dimensional operators. We then discuss relic density of dark matter and implications to collider physics in the model. The most unique signatures of this model at the LHC would be the dark scalar (${\mathrm{\ensuremath{\Phi}}}_{1}^{{(}^{\ensuremath{'}})}$) productions where it subsequently decays into: (1) a fermionic dark matter (${\ensuremath{\chi}}_{l}$) and a heavy dark fermion (${\ensuremath{\chi}}_{h}$) pair, ${\mathrm{\ensuremath{\Phi}}}_{1}^{{(}^{\ensuremath{'}})}\ensuremath{\rightarrow}{\overline{\ensuremath{\chi}}}_{l}{\ensuremath{\chi}}_{h}({\overline{\ensuremath{\chi}}}_{h}{\ensuremath{\chi}}_{l})$, followed by ${\ensuremath{\chi}}_{h}$ decays into ${\ensuremath{\chi}}_{l}$ and non-Abelian dark gauge bosons (${X}_{i}$'s) which decays into SM fermion pair ${\overline{f}}_{\mathrm{SM}}{f}_{\mathrm{SM}}$ resulting in the reaction $pp\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Phi}}}_{1}^{{(}^{\ensuremath{'}})}\ensuremath{\rightarrow}{\overline{\ensuremath{\chi}}}_{h}{\ensuremath{\chi}}_{l}({\overline{\ensuremath{\chi}}}_{l}{\ensuremath{\chi}}_{h})\ensuremath{\rightarrow}{f}_{\mathrm{SM}}{\overline{f}}_{\mathrm{SM}}{\ensuremath{\chi}}_{l}{\overline{\ensuremath{\chi}}}_{l}$, (2) a pair of ${X}_{i}$'s followed by ${X}_{i}$ decays into a DM pair or the SM fermions resulting in the reaction, $pp\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Phi}}}_{1}^{{(}^{\ensuremath{'}})}\ensuremath{\rightarrow}{X}_{i}{X}_{i}\ensuremath{\rightarrow}{\overline{\ensuremath{\chi}}}_{l}{\ensuremath{\chi}}_{l}{f}_{\mathrm{SM}}{\overline{f}}_{\mathrm{SM}}$ or even number of ${f}_{\mathrm{SM}}{\overline{f}}_{\mathrm{SM}}$ pairs.

The recently reported result from XENON1T experiment indicates that there is an excess with $3.5\sigma$ significance in the electronic recoil events. Interpreted as new physics, new sources are needed to account for the electronic scattering. We show that a dark fermion $\psi$ with mass about $ \mathcal{O}\left(10\right)$ MeV from semi-annihilation of $Z_3$ dark matter $X$ and subsequent decay of a dark gauge boson $V_\mu$ may be responsible for the excess. The relevant semi-annihilation process is $X+X\rightarrow \overline{X}+V_\mu (\rightarrow \psi + \overline{\psi})$, in which the final $\psi$ has a box-shape energy spectrum. The fast-moving $\psi$ can scatter with electron through an additional gauge boson that mixes with photon kinetically. The shape of the signals in this model can be consistent with the observed excess. The additional interaction with proton makes this model testable in future searches for nucleus recoil as well. Because of the lightness of invisible particle introduced, this scenario requires non-standard cosmology to accommodate the additional radiation component., Comment: 19 pages, 4 figures, published version

We propose a new portal coupling to dark matter by taking advantage of the nonminimally coupled portal sector to the Ricci scalar. Such a portal sector conformally induces couplings to the trace of the energy-momentum tensor of matters including highly secluded dark matter particles. The portal coupling is so feeble that dark matter is produced by freeze-in processes of scatterings and/or the decay of the mediator. We consider two concrete realizations of the portal: conformally induced Higgs portal and conformally induced mediator portal. The former case is compatible with the Higgs inflation, while the latter case can be tested by dark matter direct detection experiments., Comment: 16 pages, 5 figures, version accepted by PRD

Recently XENON1T Collaboration announced that they observed some excess in the electron recoil energy around a 2-3 keV. We show that this excess can be interpreted as exothermic scattering of excited dark matter (XDM), $XDM + e_{atomic} \rightarrow DM + e_{free}$ on atomic electron through dark photon exchange. We consider DM models with local dark $U(1)$ gauge symmetry that is spontaneously broken into its $Z_2$ subgroup by Krauss-Wilczek mechanism. In order to explain the XENON1T excess with the correct DM thermal relic density within freeze-out scenario, all the particles in the dark sector should be light enough, namely $\sim O(100)$ MeV for scalar DM and $\sim O(1-10)$ MeV for fermion DM cases. And even lighter dark Higgs $\phi$ plays an important role in the DM relic density calculation: $X X^\dagger \rightarrow Z' \phi$ for scalar DM ($X$) and $\chi \bar{\chi} \rightarrow \phi \phi$for fermion DM ($\chi$) assuming $m_{Z'} > m_\chi$. Both of them are in the $p$-wave annihilation, and one can easily evade stringent bounds from Planck data on CMB on the $s$-wave annihilations, assuming other dangerous $s$-wave annihilations are kinematically forbidden., Comment: References and a plot updated. Additional discussions on Neff

We consider a Z' model where the Z' boson couples only to up and top quarks. As a simple setup, one can consider a family-dependent $U(1)'$ symmetry, under which only right-handed up-type quarks are charged. After symmetry breaking, the right-handed quarks mix with each other and top flavor-changing neutral currents (FCNCs) mediated by the Z' boson can be generated at tree level. We take into account several processes to probe the top FCNCs, and find that the same sign top quark pair production or the triple top quark production is the most capable of testing the top FCNCs. We also consider a few non-FCNC processes to probe the Z' boson, for example, dijet production at the LHC., 21 pages, 11 figures, version published in PRD, detector simulation added

In this review, I describe a class of dark matter (DM) models where DM is either stable due to unbroken dark gauge symmetries, or long-lived due to accidental global symmetries resulting from the underlying dark gauge symmetries. Within these models, I discuss various topics on DM in the context of particle and astroparticle physics and cosmology: DM thermal relic density and (in)direct detection, Higgs inflation assisted with Higgs portal interaction, dark radiation (DR), DM-DR interaction and suppression of the matter power spectrum at large k, strong first order phase transition and gravitational wave production, etc.. Especially I emphasize the importance of dark gauge symmetries, unitarity and renormalizability, and the limitation of the DM effective field theory (EFT) or simplified models for DM searches at high energy colliders, including the role of dark Higgs boson and dark gauge bosons.

We study the Dark Matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with $\sqrt{s} = 500$ GeV. In such models, the DM pair is produced in association with a $Z$ boson. In case the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying $Z$ boson provides a better search sensitivity than the signal with leptonically decaying $Z$ boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling $g_\chi$ is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator $H_2$. And the spin discriminating from scalar DM is always promising while it is difficult to discriminate from vector DM. As for $g_\chi$ approaching the perturbative limit, benchmark points with the mediator $H_2$ in the full mass region of interest are discoverable. And the spin discriminating from both the scalar and fermion DM are quite promising., Comment: 26 pages, 9 figures, version accepted for publication in EPJC

Some interpretations of $$ {R}_{D^{\left(\ast \right)}} $$ R D ∗ anomaly in B meson decay using leptoquark (LQ) models can also generate top quark decays through Flavor Changing Neutral Current (FCNC). In this work we focus on two LQs, i.e. scalar S 1 and vector U 1 which are both singlet under the SU(2) L gauge group in the Standard Model (SM). We investigate their implications on the 3-body top FCNC decays t → cℓ i ℓ j at tree level and the 2-body t → cV at one-loop level, with ℓ being the SM leptons and V = γ, Z, g being the SM gauge bosons. We utilize the 2σ parameter fitting ranges of the LQ models and find that Br(t → cℓ i ℓ j ) at tree level can reach $$ \mathcal{O} $$ O (10−6) and Br(t → cV) at one-loop level can reach $$ \mathcal{O} $$ O (10−10). Some quick collider search prospects are also analyzed.

We study the discovery and discriminating prospects of the Higgs portal dark matter (DM) models for scalar, fermion and vector DM at the ILC with $\sqrt{s}=500$ GeV and at proton-proton (pp) collider with $\sqrt{s}=100$ TeV. For the singlet scalar DM, the mediator is just the Standard Model (SM) Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. At the 500 GeV ILC, the DM pair is dominantly produced in association with a Z boson. The distributions of DM pair invariant mass can be reconstructed. It is used as the main handle for discriminating the DM spin. At the 100 TeV $p$-$p$ collider, we consider the $t\bar{t} +$ DM associated production in dileptonic final states. The two dimensional distributions of missing transverse energy and polar angle difference between two leptons are used for a discrimination of the spin nature of DM.

It was proposed recently that different chiralities of the dark matter (DM) fermion under a broken dark U(1) gauge group can lead to distinguishable signatures at the LHC through shower patterns, which may reveal the mass origin of the dark sector. We study this subject further by examining the dark shower of two simplified models, the dubbed Chiral Model and the Vector Model. We derive a more complete set of collinear splitting functions with power corrections, specifying the helicities of the initial DM fermion and including the contribution from an extra degree of freedom, the dark Higgs boson. The dark shower is then implemented with these splitting functions, and the new features resulting from its correct modelling are emphasized. It is shown that the DM fermion chirality can be differentiated by measuring dark shower patterns, especially the DM jet energy profile, which is almost independent of the DM energy., Comment: 18 pages, 6 figures

In this article, I review a class of electroweak (EW)-scale dark-matter (DM) models where DM stability or longevity is the result of underlying dark gauge symmetries: (i) DM is stable because of unbroken local dark gauge symmetry or topology, or (ii) it is long-lived due to the accidental global symmetry of underlying dark gauge theories. Compared with the usual phenomenological dark matter models (including DM effective field theory (EFT) or simplified DM models), there are new particles in addition to DM, namely, dark gauge boson(s), dark Higgs bosons and sometimes excited dark matter, and their interactions are completely fixed by the local gauge principle. The idea of singlet portals, including the Higgs portal, can thermalize DM very efficiently so that this DM could easily be thermal DM. I also discuss the limitation of the usual DM effective field theory or simplified DM models with only unbroken $SU(3)_{\rm color} \times U(1)_{\rm em}$ gauge symmetry in the context of Higgs portal DM models and emphasize the importance of the full SM gauge symmetry and renormalizability, especially for DM searches at high-energy colliders.

We discuss the 750 GeV diphoton excess at the LHC@13TeV in the framework of leptophobic U(1)$^\prime$ model inspired by $E_6$ grand unified theory (GUT). In this model, the Standard Model (SM) chiral fermions carry charges under extra U(1)$^\prime$ gauge symmetry which is spontaneously broken by a U(1)$^\prime$-charged singlet scalar ($\Phi$). In addition, extra quarks and leptons are introduced to achieve the anomaly-free conditions, which is a natural consequence of the assumed $E_6$ GUT. These new fermions are vectorlike under the SM gauge group but chiral under new U(1)$^\prime$, and their masses come entirely from the nonzero vacuum expectation value of $\Phi$ through the Yukawa interactions. Then, the CP-even scalar $h_\Phi$ from $\Phi$ can be produced at the LHC by the gluon fusion and decay to the diphoton via the one-loop diagram involving the extra quarks and leptons, and can be identified as the origin of diphoton excess at 750 GeV. In this model, $h_\Phi$ can decay into a pair of dark matter particles as well as a pair of scalar bosons, thereby a few tens of the decay width may be possible., Comment: 21 pages, 4 figures. Published version

We construct the minimal dark matter models in the left–right symmetric extensions of the standard model (SM), where the gauge symmetry SU ( 3 ) C × SU ( 2 ) L × SU ( 2 ) R × U ( 1 ) B − L is broken into its subgroup SU ( 3 ) C × U ( 1 ) em by nonzero VEVs of a SU ( 2 ) R doublet H R and a SU ( 2 ) L × SU ( 2 ) R bidoublet H . A possible candidate of dark matter is explored in the framework of minimal dark matter considering SU ( 2 ) L , R multiplet scalar bosons and fermions. Then we focus on SU ( 2 ) R quintuplet fermions with B − L charges 0, 2 and 4 as the minimal dark matter candidates and investigate their phenomenology. We show that the dark matter in the model can provide observed relic density with 2 TeV W ′ boson which is motivated by the ATLAS diboson excess and CMS eejj excess. The possible mass of dark matter is predicted for each B − L charge. We then estimate the scattering cross section of dark matter with nucleon and production cross section of charged components in the quintuplets at the LHC.

We study the discovery and discriminating prospects of the Higgs portal dark matter (DM) models for scalar, fermion and vector DM and their extensions in proton-proton ($pp$) collisions. The $t\bar{t}+$DM associated production in dileptonic final states is considered, in which the stransverse mass of two leptons is found to be effective in suppressing the Standard Model backgrounds along with the missing transverse energy and the angle between two leptons. The distributions of missing transverse energy and polar angle between two leptons are used for a discrimination of the spin nature of DM. For the proposed benchmark points, the discovery/exclusion can be made with an integrated luminosity less than 1 ab$^{-1}$ given a 1\% systematic uncertainty, while the spin discrimination require integrated luminosity of a few O(10) ab$^{-1}$ given a 0.5\% systematic uncertainty. The DM phenomenology is also discussed. A consistent DM candidate can be obtained either by extending our model where the Higgs portal couples to excited dark states that decay into DM, or modifying the coupling form into pseudoscalar., 25 pages, 13 figures; discussions of systematic uncertainty added; matches the published version

We consider a standard model extension equipped with a dark sector where the $U(1)_X^{}$ Abelian gauge symmetry is spontaneously broken by the dark Higgs mechanism. In this framework, we investigate patterns of the electroweak phase transition as well as those of the dark phase transition, and examine detectability of gravitational waves (GWs) generated by such strongly first order phase transition. It is pointed out that the collider bounds on the properties of the discovered Higgs boson exclude a part of parameter space that could otherwise generate detectable GWs. After imposing various constraints on this model, it is shown that GWs produced by multi-step phase transitions are detectable at future space-based interferometers, such as LISA and DECIGO, if the dark photon is heavier than 25 GeV. Furthermore, we discuss the complementarity of dark photon searches or dark matter searches with the GW observations in these models with the dark gauge symmetry., Comment: 23 pages, 22 figures, version published in Journal of High Energy Physics

We consider a light dark matter candidate which is produced by the freeze-out mechanism with $3\rightarrow2$ annihilations, the so called Strongly Interacting Massive Particles (SIMPs). SIMPs are identified as dark pions in dark chiral perturbation theory (ChPT) where both light mass and strong coupling needed for SIMPs can be realized by strong dynamics. In QCD-like theories with $SU(3)_L \times SU(3)_R /SU(3)_V$ flavor symmetry, including dark vector mesons in the hidden local symmetry scheme, we illustrate that dark vector mesons unitarize the dark ChPT efficiently, thus determine the correct relic density condition within the validity of the dark ChPT., 9 pages, 4 figures, Title changed, Accepted to Physical Review D

Dark pion is the one of the most natural and realistic model to make $3 \rightarrow 2$ contact interactions among models of the Strongly Interacting Massive Particle (SIMP). In this model, there is a perturbativity problem to satisfy the relic density with the self-annihilation. So we show the perturbativity problem can be alleviated and the SIMP pion model become more realistic by including dark vector mesons., Comment: 4 pages, 2 figures, Prepared for the proceedings of the ICHEP 2018, International conference on high energy physics, 4-11 July 2018

In the supersymmetric models with low scale supersymmetry (SUSY) breaking where the gravitino mass is around keV, we show that the 3.5 keV $X-$ray lines can be explained naturally through several different mechanisms: (I) A keV scale dark gaugino plays the role of sterile neutrino in the presence of bilinear $R-$partiy violation. Because the light dark gaugino obtains Majorana mass only via gravity mediation, it is a decaying warm dark matter (DM) candidate; (II) Compressed cold DM states, whose mass degeneracy is broken by gavity mediated SUSY breaking, emit such a line via the heavier one decay into the lighter one plus photon(s). A highly supersymmetric dark sector may readily provide such kind of system; (III) Light axino, whose mass again is around the gravitino mass, decays to neutrino plus gamma in the $R-$partiy violating SUSY. Moreover, we comment on dark radiation from dark gaugino., Journal version

In this work we consider a real scalar dark matter $S$ interacting only with $SU(2)_L$ singlet Up-type quarks $U_i=u_R,c_R,t_R$ via a vector-like fermion $\psi$ which has the same quantum number as $U_i$. The DM-nucleon scattering can proceed through both $h$-mediated Higgs portal (HP) and $\psi$-mediated vector-like portal (VLP), in which HP can receive sizable radiative corrections through the new fermions. We first study the separate constraints on the new Yukawa couplings $y_i$ and find that the constraints of XENON1T results are strong on $y_1$ from VLP scattering and on $y_3$ from its radiative contributions to HP scattering. Since both DM-light quark interactions and HP have been well studied in the existing literature, we move forward to focus on DM-heavy quark interactions. Since there is no valence $c,t$ quark inside nucleons at $\mu_{\rm had}\sim 1$ GeV, $y_2,y_3$ interactions are manifested in DM-gluon scattering at loop level. We find that renormalization group equation (RGE) and heavy quark threshold effects are important if one calculates the DM-nucleon scattering rate $\sigma^{\rm SI}_{p}$ at $\mu_{\rm had}\sim 1\, {\rm GeV}$ while constructing the effective theory at $\mu_{\rm EFT}\sim m_Z$. For the benchmarks $y_3=0.5, y_2=0.5, 1, 3$, combined results from $\Omega_{\rm DM} h^2\simeq 0.12$, XENON1T, Fermi-LAT, 13 TeV LHC data have almost excluded $m_S, Comment: 30 pages, 11 figures, JCAP published version

We study an extended Standard Model with a gauged ${\mathrm{U}(1)}^{\ensuremath{'}}$ flavor symmetry, motivated not only by the fermion mass hierarchy but also by the excesses in $B\ensuremath{\rightarrow}{K}^{(*)}ll$ reported by the LHCb collaborations. The ${\mathrm{U}(1)}^{\ensuremath{'}}$ charges are assigned to quarks and leptons in a flavor-dependent manner, and flavored Higgs doublets are also introduced in order to detail the Yukawa couplings at the renormalizable level. Then, the fermion mass hierarchy is realized by the vacuum alignment of the Higgs doublets. In this model, flavor-changing currents involving the gauge boson of ${\mathrm{U}(1)}^{\ensuremath{'}}$ and the scalars generated by the Higgs doublets are predicted and the observables in the $B\ensuremath{\rightarrow}{K}^{(*)}ll$ process possibly deviate from the Standard Model predictions. We study the possibility that these new flavor-changing interactions can explain the excesses in the $B\ensuremath{\rightarrow}{K}^{(*)}ll$ process, and we derive some predictions for the other flavor-violating processes based on the analysis. We specifically investigate the $\mathrm{\ensuremath{\Delta}}F=2$ processes and the other $B$ decays: e.g., $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ and $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\ensuremath{\nu}$, where the deviations are reported by the Belle and BABAR collaborations.

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 added

We propose a scenario to generate flavor violating ${Z}^{\ensuremath{'}}$ interactions at one-loop level by introducing $U(1{)}_{\ensuremath{\mu}\ensuremath{-}\ensuremath{\tau}}$ gauge symmetry, extra vectorlike quark doublets ${Q}_{a}^{\ensuremath{'}}$, and a singlet scalar $\ensuremath{\chi}$. Both ${Q}_{a}^{\ensuremath{'}}$ and $\ensuremath{\chi}$ are charged under $U(1{)}_{\ensuremath{\mu}\ensuremath{-}\ensuremath{\tau}}$ and carry odd dark ${Z}_{2}$ parity. Assuming that $\ensuremath{\chi}$ is the dark matter (DM) of the Universe and imposing various constraints from a dark matter search, flavor physics, and a collider search for ${Q}_{a}^{\ensuremath{'}}$, one can show that radiative corrections to $b\ensuremath{\rightarrow}s{Z}^{\ensuremath{'}*}\ensuremath{\rightarrow}s{l}^{+}{l}^{\ensuremath{-}}$ involving ${Q}_{a}^{\ensuremath{'}}$ and $\ensuremath{\chi}$ can induce $\mathrm{\ensuremath{\Delta}}{C}_{9}\ensuremath{\sim}\ensuremath{-}1$, which can resolve the LHCb anomalies related with $B\ensuremath{\rightarrow}{K}^{(*)}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$. Therefore, both DM and $B$ physics anomalies can be accommodated in the model.

We revisit the sensitivity study of the Tokai-to-Kamioka-and-Korea (T2KK) and Tokai-to-Kamioka-and-Oki (T2KO) proposals where a water Cerenkov detector with the 100 kton fiducial volume is placed in Korea ($L = 1000$ km) and Oki island ($L = 653$ km) in Japan, respectively, in addition to the Super-Kamiokande for determination of the neutrino mass hierarchy and leptonic CP phase ($\delta_{CP}$). We systematically study the running ratio of the $\nu_\mu$ and $\bar{\nu}_\mu$ focusing beams with dedicated background estimation for the $\nu_e$ appearance and $\nu_\mu$ disappearance signals, especially improving treatment of the neutral current $\pi^0$ backgrounds. Using a $\nu_\mu$ - $\bar{\nu}_\mu$ beam ratio between 3 : 2 and 2.5 : 2.5 (in unit of $10^{21}$POT with the proton energy of 40 GeV), the mass hierarchy determination with the median sensitivity of 3 - 5 $\sigma$ by the T2KK and 1 - 4 $\sigma$ by the T2KO experiment are expected when $\sin^2\theta_{23} = 0.5$, depending on the mass hierarchy pattern and CP phase. These sensitivities are enhanced (reduced) by $30\%$ - $40\%$ in $\Delta \chi^2$ when $\sin^2\theta_{23} = 0.6\, (0.4)$. The CP phase is measured with the uncertainty of $20^\circ$ - $50^\circ$ by the T2KK and T2KO using the $\nu_\mu$ - $\bar{\nu}_\mu$ focusing beam ratio between 3.5 : 1.5 and 1.5 : 3.5. These findings indicate that inclusion of the $\bar{\nu}_\mu$ focusing beam improves the sensitivities of the T2KK and T2KO experiments to both the mass hierarchy determination and leptonic CP phase measurement simultaneously with the preferred beam ratio being between 3 : 2 - 2.5 : 2.5 ($\times 10^{21}$POT).

We propose an interesting framework for asymmetric scalar dark matter (ADM), which has novel collider phenomenology in terms of an unstable ADM bound state (ADMonium) produced via Higgs portals. ADMonium is a natural consequence of the basic features of ADM: the (complex scalar) ADM is charged under a dark local $U(1)_d$ symmetry which is broken at a low scale and provides a light gauge boson $X$. The dark gauge coupling is strong and then ADM can annihilate away into $X$-pair effectively. Therefore, the ADM can form bound state due to its large self-interaction via $X$ mediation. To explore the collider signature of ADMonium, we propose that ADM has a two-Higgs doublet portal. The ADMonium can have a sizable mixing with the heavier Higgs boson, which admits a large cross section of ADMonium production associated with $b\bar b$. The resulting signature at the LHC depends on the decays of $X$. In this paper we consider a case of particular interest: $pp\ra b\bar b+ {\rm ADMonium}$ followed by ${\rm ADMonium}\ra 2X\ra 2e^+e^-$ where the electrons are identified as (un)converted photons. It may provide a competitive explanation to heavy di-photon resonance searches at the LHC., PRD version; major revision in terms of the referee's reports; building a new model to avoid the strong DM direct detection constraint; new references added

We propose a novel particle physics model in which vector dark matter (VDM) and dark radiation (DR) originate from the same non-Abelian dark sector. We show an illustrating example where dark $SU(3)$ is spontaneously broken into $SU(2)$ subgroup by the nonzero vacuum expectation value of a complex scalar in fundamental representation of $SU(3)$. The massless gauge bosons associated with the residual unbroken $SU(2)$ constitute DR and help to relieve the tension in Hubble constant measurements between $\textit{Planck}$ and Hubble Space Telescope. In the meantime, massive dark gauge bosons associated with the broken generators are VDM candidates. Intrinsically, this non-Abelian VDM can interact with non-Abelian DR in the cosmic background, which results in a suppressed matter power spectrum and leads to a smaller $\sigma_8$ for structure formation., Comment: 17 pages, 6 figures, updated discussions; Published version

We propose a predictive radiative seesaw model at one-loop level with a flavor dependent gauge symmetry $U(1)_{xB_3-xe-\mu+\tau}$ and Majorana fermion dark matter. For the neutrino mass matrix, we obtain an $A_1$ type texture (with two zeros) that provides us several predictions such as the normal ordering for the neutrino masses. We analyze the constraints from lepton flavor violations, relic density of dark matter, and collider physics for the new $U(1)_{xB_3-xe-\mu+\tau}$ gauge boson. Within the allowed region, the LHCb anomalies in $B\rightarrow K^* \mu^+ \mu^-$ and $B\rightarrow K \ell^+ \ell^-$ with $\ell=e$ or $\mu$ can be resolved, and such $Z'$ could be also observed at the LHC., Comment: 17 pages, 3 figures, 2 tables, published version

We consider a minimal renormalizable and gauge invariant dark matter (DM) model, in which the singlet fermion DM has only axial couplings to a new pseudoscalar mediator. The mixing between the pseudoscalar mediator and the standard model (SM) Higgs boson induces the interactions between the DM and SM particles. The DM candidate in this model can provide the correct thermal relic density and evades all direct detections, while it can produce observable signals in indirect detection experiments due to its large annihilation cross section. A comparative study for DM phenomenology at the LHC is conducted for models with scalar mediators that have either scalar or pseudoscalar couplings to SM particles and the DM. We find that the three scenarios have distinguishable features in scalar decay branching ratio, DM pair production cross section as well as the signal reaches at the LHC. The LHC searches for some visible signals related to the scalar sector are also discussed., Comment: 9 pages, 8 figures; to appear in Phys. Rev. D

In the light of recent possible tensions in the Hubble constant $H_0$ and the structure growth rate $\sigma_8$ between the Planck and other measurements, we investigate a hidden-charged dark matter (DM) model where DM interacts with hidden chiral fermions, which are charged under the hidden SU(N) and U(1) gauge interactions. The symmetries in this model assure these fermions to be massless. The DM in this model, which is a Dirac fermion and singlet under the hidden SU(N), is also assumed to be charged under the U(1) gauge symmetry, through which it can interact with the chiral fermions. Below the confinement scale of SU(N), the hidden quark condensate spontaneously breaks the U(1) gauge symmetry such that there remains a discrete symmetry, which accounts for the stability of DM. This condensate also breaks a flavor symmetry in this model and Nambu-Goldstone bosons associated with this flavor symmetry appear below the confinement scale. The hidden U(1) gauge boson and hidden quarks/Nambu-Goldstone bosons are components of dark radiation (DR) above/below the confinement scale. These light fields increase the effective number of neutrinos by $\delta N_{\rm eff}\simeq 0.59$ above the confinement scale for $N=2$, resolving the tension in the measurements of the Hubble constant by Planck and Hubble Space Telescope if the confinement scale is $\lesssim 1$ eV. DM and DR continuously scatter with each other via the hidden U(1) gauge interaction, which suppresses the matter power spectrum and results in a smaller structure growth rate. The DM sector couples to the Standard Model sector through the exchange of a real singlet scalar mixing with the Higgs boson, which makes it possible to probe our model in DM direct detection experiments. Variants of this model are also discussed, which may offer alternative ways to investigate this scenario., Comment: 20 pages, 4 figures; v2: version accepted for publication in PLB

We consider the Higgs-dilaton(radion) system using the trace of energy-momentum tensor ($T_{~\mu}^\mu$) 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 $T_{~\mu}^\mu$ 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 scalar bosons and the Higgs-dilaton mixing changes the scalar phenomenology in interesting ways. The signal strengths for the $gg$-initiated channels could be modified significantly compared with the SM predictions due to the QCD scale anomaly and the Higgs-dilaton(radion) mixing, whereas anomaly contributions are almost negligible for other channels. We also discuss the self-couplings and the signal strengths of the $126$ GeV scalar boson in various channels and possible constraints from the extra light/heavy scalar boson. The Higgs-dilaton(radion) system considered in this work has a number of distinctive features that could be tested by the upcoming LHC running and at the ILC., Comment: Minor corrections, including a few new figures, version appearing in Physics Letters B

We consider dark matter physics in a model for the dark sector with extra dark U(1)X gauge symmetry. The dark sector is composed of exotic fermions that are charged under both dark U(1)X and the standard model SU(3)C×U(1)Y gauge groups, as well as standard model singlet complex scalarsand X with nonzero U(1)X charge. In this model, there are two dark matter candidates−a scalar and a fermion−both of which are stabilized by accidental Z2 symmetry. Their thermal relic density, and direct and indirect detection constraints are discussed in detail and we search for the parameter space of the model accommodating dark matter observations. We also discuss constraints from diphoton resonance searches associated with the scalar field which breaks the dark U(1)X, in a way consistent with dark matter physics. In addition, implications for collider physics are discussed, focusing on the production cross section of the scalar boson.

In this talk, I describe a class of electroweak (EW) scale dark matter (DM) models where its stability or longevity are the results of underlying dark gauge symmetries: stable due to unbroken local dark gauge symmetry or topology, or long-lived due to the accidental global symmetry of dark gauge theories. Compared with the usual phenomenological dark matter models (including DM EFT or simplified DM models), DM models with local dark gauge symmetries include dark gauge bosons, dark Higgs bosons and sometimes excited dark matter. And dynamics among these fields are completely fixed by local gauge principle. The idea of singlet portals including the Higgs portal can thermalize these hidden sector dark matter very efficiently, so that these DM could be easily thermal DM. I also discuss the limitation of the usual DM effective field theory or simplified DM models without the full SM gauge symmetry, and emphasize the importance of the full SM gauge symmetry and renormalizability especially for collider searches for DM., Comment: Proceeding for DSU2015, Corfu 2015, CosPA 2015 with similar titles. arXiv admin note: text overlap with arXiv:1503.05412