Dark photons as fractional cosmic neutrino masquerader

Recently, Weinberg proposed a Higgs portal model with a spontaneously broken global U(1) symmetry in which Goldstone bosons may be masquerading as fractional cosmic neutrinos. We extend the model by gauging the U(1) symmetry. This gives rise to the so-called dark photon and dark Higgs. The dark photons can constitute about 0.912 (0.167) to the effective number of light neutrino species if they decouple from the thermal bath before the pions become non-relativistic and after (before) the QCD transition. Restriction on the parameter space of the portal coupling and the dark Higgs mass is obtained from the freeze-out condition of the dark photons. Combining with the collider data constraints on the invisible width of the standard model Higgs requires the dark Higgs mass to be less than a few GeV

Dark Z implication for flavor physics

Dark Z /dark photon ( Z ′ ) is one candidate of dark force carrier, which helps to interpret the properties of dark matter (DM). Other than conventional studies of DM including direct detection, indirect detection and collider simulation, in this work we take flavor physics as a complementary approach to investigate the features of dark matter. We give an exact calculation of the new type of penguin diagram induced by Z ′ which further modifies the well-known X, Y, Z functions in penguin-box expansion. The measurement of rare decays B → K (*) μ + μ − and B s → μ + μ − at LHC, together with direct CP violation ε ′ /ε in K → ππ as well as K L → μ + μ − , are used to determine the parameter space. The size of coupling constant, however, is found to be O 1 $$\mathcal{O}(1)$$ which is much weaker than the known constraints

Breakdown of QCD factorization for P-wave quarkonium production at low transverse momentum

Quarkonium production at low transverse momentum in hadron collisions can be used to extract Transverse-Momentum-Dependent (TMD) gluon distribution functions, if TMD factorization holds there. We show that TMD factorization for the case of P-wave quarkonium with JPC=0++,2++ holds at one-loop level, but is violated beyond one-loop level. TMD factorization for other P-wave quarkonium is also violated already at one-loop level

Higgs pair production with SUSY QCD correction: revisited under current experimental constraints

We consider the current experimental constraints on the parameter space of the MSSM and NMSSM. Then in the allowed parameter space we examine the Higgs pair production at the 14 TeV LHC via $b\overline{b}$ → hh ( h is the 125 GeV SM-like Higg boson) with one-loop SUSY QCD correction and compare it with the production via gg → hh . We obtain the following observations: (i) For the MSSM the production rate of $b\overline{b}$ → hh can reach 50 fb and thus can be competitive with gg → hh , while for the NMSSM $b\overline{b}$ → hh has a much smaller rate than gg → hh due to the suppression of the $hb\overline{b}$ coupling; (ii) The SUSY-QCD correction to $b\overline{b}$ → hh is sizable, which can reach 45% for the MSSM and 15% for the NMSSM within the 1 σ region of the Higgs data; (iii) In the heavy SUSY limit (all soft mass parameters become heavy), the SUSY effects decouple rather slowly from the Higgs pair production (especially the gg → hh process), which, for M SUSY = 5 TeV and m A < 1 TeV, can enhance the production rate by a factor of 1.5 and 1.3 for the MSSM and NMSSM, respectively. So, the Higgs pair production may be helpful for unraveling the effects of heavy SUSY

Higgs phenomenology in the Minimal Dilaton Model after Run I of the LHC

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 one considers the ATLAS and CMS data separately, the MDM can explain each of them well, but refer to different parameter space due to the apparent difference in the two sets of data. If one considers the combined data of the LHC and Tevatron, however, the explanation given by the MDM is not much better than the SM, and the dilaton component in the 125-GeV Higgs is less than about 20 % at 2σ level. (ii) The current Higgs data have stronger constrains on the light dilaton scenario than on the heavy dilaton scenario. (iii) The heavy dilaton scenario can produce a Higgs triple self coupling much larger than the SM value, and thus a significantly enhanced Higgs pair cross section at hadron colliders. With a luminosity of 100 fb −1 (10 fb −1 ) at the 14-TeV LHC, a heavy dilaton of 400 GeV (500 GeV) can be examined. (iv) In the light dilaton scenario, the Higgs exotic branching ratio can reach 43 % (60 %) at 2σ (3σ) level when considering only the CMS data, which may be detected at the 14-TeV LHC with a luminosity of 300 fb −1 and the Higgs Factory

On the momentum dependence of the flavor structure of the nucleon sea

Difference between the u¯ and d¯ sea quark distributions in the proton was first observed in the violation of the Gottfried sum rule in deep-inelastic scattering (DIS) experiments. The parton momentum fraction x dependence of this difference has been measured over the region 0.02<x<0.35 from Drell–Yan and semi-inclusive DIS experiments. The Drell–Yan data suggested a possible sign-change for d¯(x)−u¯(x) near x∼0.3 , which has not yet been explained by existing theoretical models. We present an independent evidence for the d¯(x)−u¯(x) sign-change at x∼0.3 from an analysis of the DIS data. We further discuss the x -dependence of d¯−u¯ in the context of meson cloud model and the lattice QCD formulation

Explanation of the ATLAS Z-peaked excess in the NMSSM

Recently the ATLAS collaboration reported a 3σ excess in the leptonic- Z + jets + E T miss channel. This may be interpreted in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) by gluino pair production with the decay chain g ˜ → q q ¯ χ ˜ 2 0 → q q ¯ Z χ ˜ 1 0 $$\tilde{g}\to q\overline{q}{\tilde{\chi}}_2^0\to q\overline{q}Z{\tilde{\chi}}_1^0$$ , where χ ˜ 1 0 $${\tilde{\chi}}_1^0$$ and χ ˜ 2 0 $${\tilde{\chi}}_2^0$$ denote the lightest and the next-to-lightest neutralinos with singlino and bino as their dominant components respectively. After exploring the relevant parameter space of the NMSSM by considering the constraints from the ATLAS searches for jets + E T miss signals, we conclude that the NMSSM is able to explain the excess at 1 σ level with the number of the signal events reaching its measured central value in optimal cases, and the best explanation comes from a compressed spectrum such as m g ˜ ≃ 650 $${m}_{\tilde{g}}\simeq 650$$ GeV, m χ ˜ 2 0 ≃ 565 $${m}_{{\tilde{\chi}}_2^0}\simeq 565$$ and m χ ˜ 1 0 ≃ 465 $${m}_{{\tilde{\chi}}_1^0}\simeq 465$$ GeV. We also check the consistency of the ATLAS results with the null result of the CMS on- Z search. We find that under the CMS limits at 95% C.L., the event number of the ATLAS on- Z signal can still reach 11 in our scenario, which is about 1 . 2 σ away from the measured central value

An updated analysis of Inert Higgs Doublet Model in light of the recent results from LUX, PLANCK, AMS-02 and LHC

In light of the recent discovery by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) of a Higgs-like particle with a narrow mass range of 125–126 GeV, we perform an updated analysis on one of the popular scalar dark matter models, the Inert Higgs Doublet Model (IHDM). We take into account in our likelihood analysis of various experimental constraints, including recent relic density measurement, dark matter direct and indirect detection constraints as well as the latest collider constraints on the invisible decay width of the Higgs boson and monojet search at the LHC. It is shown that if the invisible decay of the standard model Higgs boson is open, LHC as well as direct detection experiments like LUX and XENON100 could put stringent limits on the Higgs boson couplings to dark matter. We find that the most favoured parameter space for IHDM corresponds to dark matter with a mass less than 100 GeV or so. In particular, the best-fit points are at the dark matter mass around 70 GeV where the invisible Higgs decay to dark matter is closed. Scalar dark matter in the higher mass range of 0.5–4 TeV is also explored in our study. Projected sensitivities for the future experiments of monojet at LHC-14, XENON1T and AMS-02 one year antiproton flux are shown to put further constraints on the existing parameter space of IHDM

SUSY induced top quark FCNC decay t→ch after Run I of LHC

In light of the Higgs discovery and the nonobservation of sparticles at the LHC, we revisit the supersymmetric theory (SUSY) induced top quark flavor-changing decay into the Higgs boson. We perform a scan over the relevant SUSY parameter space by considering the constraints from the Higgs mass measurement, the LHC search for SUSY, the vacuum stability, the precision electroweak observables as well as B→Xsγ . We make the following observations: (1) In the Minimal Supersymmetric Standard Model (MSSM), the branching ratio of t→ch can only reach 3.0×10-6 , which is about one order smaller than previous results obtained before the advent of the LHC. Among the considered constraints, the Higgs mass and the LHC search for sparticles are found to play an important role in limiting the prediction. (2) In the singlet extension of the MSSM, since the squark sector is less constrained by the Higgs mass, the branching ratio of t→ch can reach the order of 10-5 in the allowed parameter space. (3) The chiral-conserving mixings δLL and δRR may have remanent effects on t→ch in the heavy SUSY limit. In the MSSM with squarks above 3 TeV and gluino above 4 TeV and meanwhile the CP-odd Higgs boson mass around 1 TeV, the branching ratio of t→ch can still reach the order of 10-8 under the constraints

QCD corrections of all structure functions in transverse momentum dependent factorization for Drell-Yan processes

We study the one-loop correction in Transverse-Momentum-Dependent(TMD) factorization for Drell-Yan processes at small transverse momentum of the lepton pair. We adopt the so-called subtractive approach, in which one can systematically construct contributions for subtracting long-distance effects represented by diagrams. The perturbative parts are obtained after the subtraction. We find that the perturbative coefficients of all structure functions in TMD factorization at leading twist are the same. The perturbative parts can also be studied with scattering of partons instead of hadrons. In this way, the factorization of many structure functions can only be examined by studying the scattering of multi-parton states, where there are many diagrams. These diagrams have no similarities to those treated in the subtractive approach. As an example, we use existing results of one structure function responsible for Single-Spin-Asymmetry, to show that these diagrams in the scattering of multi-parton states are equivalent to those treated in the subtractive approach after using Ward identity