Recent claims of a line in the Fermi-LAT photon spectrum at 130 GeV are suggestive of dark matter annihilation in the galactic center and other dark matter-dominated regions. If the Fermi feature is indeed due to dark matter annihilation, the best-fit line cross-section, together with the lack of any corresponding excess in continuum photons, poses an interesting puzzle for models of thermal dark matter: the line cross-section is too large to be generated radiatively from open Standard Model annihilation modes, and too small to provide efficient dark matter annihilation in the early universe. We discuss two mechanisms to solve this puzzle and illustrate each with a simple reference model in which the dominant dark matter annihilation channel is photonic final states. The first mechanism we employ is resonant annihilation, which enhances the annihilation cross-section during freezeout and allows for a sufficiently large present-day annihilation cross section. Second, we consider cascade annihilation, with a hierarchy between p-wave and s-wave processes. Both mechanisms require mass near-degeneracies and predict states with masses closely related to the dark matter mass; resonant freezeout in addition requires new charged particles at the TeV scale.
Indications for a gamma-ray line(s) signal towards the Galactic center at an energy of about 130 GeV have been recently presented. While dark matter annihilations are a viable candidate for this signal, it is generally expected that such a flux would be correlated to a gamma-ray component with continuum energy spectrum due to dark matter pair annihilating into other Standard Model particles. We use the gamma-ray data from the inner 10 x 10 degree window to derive limits for a variety of DM annihilation final states. Extending the window of observation, we discuss bounds on the morphological sh…
There is evidence for a 130 GeV gamma-ray line at the Galactic Center in the Fermi Large Area Telescope data. Dark matter candidates that explain this feature should also annihilate to Standard Model particles, resulting in a continuous spectrum of photons. To study this continuum, we analyze the Fermi data down to 5 GeV, restricted to the inner 3 degrees of the Galaxy. We place a strong bound on the ratio of continuum photons to monochromatic line photons that is independent of uncertainties in the dark matter density profile. The derived constraints exclude neutralino dark matter as an expla…
We study the most recently observed excited $B_{c}$ states with the Dyson-Schwinger equation and the Bethe-Salpeter equation approach of continuum QCD. The obtained $M_{B^+_{c}(2S)}=6.813(16)\text{GeV}$, $M_{B^{*+}_{c}(2S)}=6.841(18)\text{GeV}$ and the mass splitting $M_{B_c^+(2S)}-M^{\text{rec}}_{B_c^{*+}(2S)} \approx 0.039 \text{GeV}$ agree with the observations very well. Moreover we predict the leptonic decay constant $f_{B^+_{c}(2S)}=-0.165(10)\text{GeV}$, $f_{B^{*+}_{c}(2S)}=-0.161(7)\text{GeV}$ respectively.
The new scalar resonance contribution to the 750 GeV diphoton excess observed at the LHC 13 TeV necessarily interferes with the continuum background in the $gg\to γγ$. The interference has two considerable effects: (1) enhancing or suppressing diphoton signal rate due to the imaginary-part interference and (2) distorting resonance shape due to the real-part interference. From the best-fit study of two benchmark models (two Higgs doublets with $\sim$50 GeV widths and a singlet scalar with 5 GeV width, both extended with vector-like fermions), we find that the resonance contribution to the 750 G…
We compute charm and bottom quark masses in the quenched approximation and in the continuum limit of lattice QCD. We make use of a step scaling method, previously introduced to deal with two scale problems, that allows to take the continuum limit of the lattice data. We determine the RGI quark masses and make the connection to the MSbar scheme. The continuum extrapolation gives us a value m_b^{RGI} = 6.73(16) GeV for the b-quark and m_c^{RGI} = 1.681(36) GeV for the c-quark, corresponding respectively to m_b^{MSbar}(m_b^{MSbar}) = 4.33(10) GeV and m_c^{MSbar}(m_c^{MSbar}) = 1.319(28) GeV. The …
Using the soft-pion theorem and the assumption on the final-state interactions, we include the contribution of $DK$ continuum into the QCD sum rules for $D_{sJ}(2317)$ meson. We find that this contribution can significantly lower the mass and the decay constant of $D_s(0^+)$ state. For the value of the current quark mass $m_c(m_c)=1.286 {\rm GeV}$, we obtain the mass of $D_s(0^+)$ $M=2.33 \pm 0.02 {\rm GeV}$ in the interval $s_0=7.5-8.0 {\rm GeV}^2$, being in agreement with the experimental data, and the vector current decay constant of $D_s(0^+)$ $f_0=0.128 \pm 0.013 {\rm GeV}$, much lower th…
An analysis of the Fermi gamma ray space telescope data has recently revealed a resolved gamma-ray feature close to the galactic center which is consistent with monochromatic photons at an energy of about 130 GeV. If interpreted in terms of dark matter (DM) annihilating into γγ(γZ, γh), this would correspond to a DM particle mass of roughly 130 GeV (145 GeV, 155 GeV). The rate for these loop-suppressed processes, however, is larger than typically expected for thermally produced DM. Correspondingly, one would generically expect even larger tree level production rates of standard model fermions …
We generalize the recently proposed continuum dark matter model to the case where the dark matter consists of a spin-$1/2$ or spin-$1$ gapped continuum. We construct simple continuum analogs of weakly interacting massive particles annihilating through the $Z$ portal. We discuss all existing experimental constraints, with the strongest bounds arising from indirect detection and limits on continuum decays from the cosmic microwave background. Our models are phenomenologically viable for gap scales of $60$-$200$ GeV (spin-$1/2$) and $35$-$90$ GeV (spin-$1$), owing to the strong kinematic suppress…
The viability of neutralino dark matter as an explanation of the 130 GeV gamma ray signal from the Galactic Center recently observed by the Fermi Large Area Telescope is examined. It is found that the signal can be compatible with a sharp feature from internal bremsstrahlung from a mostly bino dark matter particle of mass around 145 GeV, augmented by a contribution from annihilation into gamma+Z via a small wino admixture. This scenario circumvents the problematic overproduction of lower energy continuum photons that plague line interpretations of this signal. Sleptons approximately degenerate…
We compute the strange and the average up/down quark masses in the quenched approximation of lattice QCD, by using the O(a)-improved Wilson action and operators and by implementing the non-perturbative renormalization. Our computation is performed at four values of the lattice spacing, from which we could extrapolate to the continuum limit. Our final result for the strange quark mass (in the MSbar scheme) is ms(2 GeV) = (106 +/- 2 +/- 8) MeV. For the average up/down quark mass we have ml(2 GeV) = (4.4 +/- 0.1 +/- 0.4) MeV. The ratio ms/ml = (24.3 +/- 0.2 +/- 0.6).
We study a two Higgs doublet model augmented by a scalar dark matter particle that provides an excellent fit to the LHC Higgs data and the Fermi-LAT 135 GeV line. The heavy CP-even Higgs boson, which predominantly mediates annihilation and scattering, must have a coupling to weak gauge bosons at or below percent level to suppress the continuum gamma-ray spectrum below the limit from the Fermi-LAT data and the anti-proton spectrum constrained by the PAMELA data. Discovering or excluding this CP-even Higgs boson at the LHC with a mass between 265 and 280 GeV and an enhanced diphoton branching ra…
We present new results for the amplitude $A_2$ for a kaon to decay into two pions with isospin $I=2$: Re$A_2 = 1.50(4)_\mathrm{stat}(14)_\mathrm{syst}\times 10^{-8}$ GeV; Im$A_2 = -6.99(20)_\mathrm{stat}(84)_\mathrm{syst}\times 10^{-13}$ GeV. These results were obtained from two ensembles generated at physical quark masses (in the isospin limit) with inverse lattice spacings $a^{-1}=1.728(4)$ GeV and $2.358(7)$ GeV. We are therefore able to perform a continuum extrapolation and hence largely to remove the dominant systematic uncertainty from our earlier results, that due to lattice artefacts. …
We present a quenched lattice QCD calculation of the αand βparameters of the proton decay matrix element. The simulation is carried out using the Wilson quark action at three values of the lattice spacing in the range a\approx 0.1-0.064 fm to study the scaling violation effect. We find only mild scaling violation when the lattice scale is determined by the nucleon mass. We obtain in the continuum limit, |α(NDR,2GeV)|=0.0090(09)(^{+5}_{-19})GeV^3 and |β(NDR,2GeV)|=0.0096(09)(^{+6}_{-20})GeV^3 with αand βin a relatively opposite sign, where the first error is statistical and the second is due to…
Recent radio observations have obtained stringent constraints for annihilating dark matter. In this article, we use the radio continuum spectral data of the Large Magellanic Cloud (LMC) to analyze the dark matter annihilation signals. We have discovered a slightly positive signal of dark matter annihilation with a $1.5σ$ statistical significance. The overall best-fit dark matter mass is $m_{\rm DM} \approx 90$ GeV, annihilating via $b\bar{b}$ channel. We have also constrained the $3σ$ lower limits of dark matter mass with the standard thermal dark matter annihilation cross section for the $e^+…
We use lattice QCD simulations, with MILC gluon configurations and HISQ c-quark propagators, to make very precise determinations of moments of charm-quark pseudoscalar, vector and axial-vector correlators. These moments are combined with new four-loop results from continuum perturbation theory to obtain several new determinations of the MSbar mass of the charm quark and of the MSbar coupling. We find m_c(3GeV)=0.986(10)GeV, or, equivalently, m_c(m_c)=1.268(9)GeV, both for n_f=4 flavors; and alpha_msb(3GeV,n_f=4)=0.251(6), or, equivalently, alpha_\msb(M_Z,n_f=5)=0.1174(12). The new mass agrees …
Using the results of several quenched lattice simulations, we predict the value of the strange and charm quark masses in the continuum at the next-to-leading order, $m^{\overline{MS}}_s(μ=2\,\, \rm{GeV})= (127 \pm 18)\,\, \rm{MeV}$ and $m^{\overline{MS}}_{ch}(μ=2 \,\,\rm{GeV})=(1.47 \pm 0.28)\,\, \rm{GeV}$. The errors quoted above have been estimated by taking into account the original statistical error of the lattice results and the uncertainties coming from the matching of the lattice to the continuum theory. A detailed presentation of the relevant formulae at the next-to-leading order and a…
We present physical results obtained from simulations using 2+1 flavors of domain wall quarks and the Iwasaki gauge action at two values of the lattice spacing $a$, ($a^{-1}$=\,1.73\,(3)\,GeV and $a^{-1}$=\,2.28\,(3)\,GeV). On the coarser lattice, with $24^3\times 64\times 16$ points, the analysis of ref.[1] is extended to approximately twice the number of configurations. The ensembles on the finer $32^3\times 64\times 16$ lattice are new. We explain how we use lattice data obtained at several values of the lattice spacing and for a range of quark masses in combined continuum-chiral fits in or…
We show that decaying axino dark matter with R-parity violation can explain the observed excess of the 130GeV gamma-ray line from the Galactic center in the Fermi data. The branching fraction of the axino decay into monochromatic photons can be O(1), and constraints from continuum gamma-rays and the anti-proton flux are ameliorated. The Peccei-Quinn scale of $O(10^{13}-10^{14})$\,GeV and the R-parity violation parameter of $O(10^{-12}-10^{-11})$ are cosmologically favored.
We propose a novel mechanism enabling us to have a continuum bump as a signature of gamma-ray excess in indirect detection experiments of dark matter (DM), postulating a generic dark sector having (at least) two DM candidates. With the assumption of non-zero mass gap between the two DM candidates, the heavier one directly communicates to the partner of the lighter one. Such a partner then decays into a lighter DM particle along with an "axion-like" particle (ALP) or dark "pion", which subsequently decays into a pair of photons, via a more-than-one step cascade decay process. Since the cascade …
We study the effect of interference between the Standard Model Higgs boson resonance and the continuum background in the process gamma gamma -> H -> b b-bar at a photon collider. Taking into account virtual gluon exchange between the final-state quarks, we calculate the leading corrections to the height of the resonance for the case of a light (m_H < 160 GeV) Higgs boson. We find that the interference is destructive and around 0.1--0.2% of the peak height, depending on the mass of the Higgs and the scattering angle. This suppression is smaller by an order of magnitude than the anticipated expe…
Scattering of sub-GeV dark matter (DM) particles with hydrogen atoms is studied in this paper. The interactions of DM with electrons and nucleons are both included and formulated in a general framework based on nonrelativistic effective field theory. On the assumption of same dark matter coupling strengths, it is found that DM-electron interactions dominate the inelastic atomic transitions to discrete excited states and ionization continuum around the threshold regions, and DM-nucleon interactions become more important with increasing energy and dominate in elastic scattering. The conclusion s…
We present a study of the compatibility of some current models of the diffuse Galactic continuum gamma rays with EGRET data. A set of regions sampling the whole sky is chosen to provide a comprehensive range of tests. The range of EGRET data used is extended to 100 GeV. The models are computed with our GALPROP cosmic-ray propagation and gamma-ray production code. We confirm that the "conventional model" based on the locally observed electron and nucleon spectra is inadequate, for all sky regions. A conventional model plus hard sources in the inner Galaxy is also inadequate, since this cannot e…
A Lattice QCD study of $p-Λ$ scattering in continuum and chiral limits
Shanghai Normal University（上海师范大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心）；School of Physics, Peking University（北京大学物理学院）
The $ϕ^4_3$ model at finite temperature is simulated on the lattice. For fixed $N_t$ we compute the transition line for $N_s \to \infty$ by means of Finite Size Scaling techniques. The crossings of a Renormalization Group trajectory with the transition lines of increasing $N_t$ give a well defined limit for the critical temperature in the continuum. By considering different RG trajectories, we compute $T^c/g$ as a function of the renormalized parameters.
