Observational limits on the high-energy neutrino background have been used to place general constraints on dark matter that annihilates only into standard model particles. Dark matter particles that annihilate into neutrinos will also inevitably branch into electromagnetic final states through higher-order tree and loop diagrams that give rise to charged leptons, and these charged particles can transfer their energy into photons via synchrotron radiation or inverse Compton scattering. In the context of effective field theory, we calculate the loop-induced branching ratio to charged leptons and show that it is generally quite large, typically >1%, when the scale of the dark matter mass exceeds the electroweak scale, M_W. For a branching fraction >3%, the synchrotron radiation bounds on dark matter annihilation are currently stronger than the corresponding neutrino bounds in the interesting mass range from 100 GeV to 1 TeV. For dark matter masses below M_W, our work provides a plausible framework for the construction of a model for "neutrinos only" dark matter annihilations.
We use classical or large Nc QCD to describe the mesons (pion, rho, omega) coming from proton-antiproton annihilation at rest as classical fields, which we then quantize as coherent states. This treatment gives a nearly parameter free account of the pion branching ratios in annihilation.
Recursive solution for a general homogeneous in time pure birth branching process with simultaneous production of any number of particles and with continuous evolution parameter is given. Calculational algorithm based on the use of Koenigs function and functional Schroder equation is described. It is shown that multiplicity distributions in e+e- annihilation into hadrons for c.m. energies up to 189 GeV are well described by the modified negative binomial distribution, explained by simple pure birth branching process without multiple simultaneous particle production. The energy dependence of th…
We give some remarks on the $\bar n p$-partial branching ratios in flight at low momenta of antineutron, measured by OBELIX collaboration. The comparison is made to the known branching ratios from the $p \bar p$-atomic states. The branching ratio for the reaction $\bar n p \to π^+π^0$ is found to be suppressed in comparison to what follows from the $ p \bar p$-data. It is also shown, that there is no so called dynamic I=0-amplitude suppression for the process $N\bar N \to K\bar K$.
With heavy quark limit and hierarchy approximation $λ_{QCD}\ll m_D\ll m_B$, we analyze the $B\to D^0\bar D^0$ and $B_s\to D^0\bar D^0$ decays, which occur purely via annihilation type diagrams. As a roughly estimation, we calculate their branching ratios and CP asymmetries in Perturbative QCD approach. The branching ratio of $B\to D^0\bar D^0$ is about $3.8\times10^{-5}$ that is just below the latest experimental upper limit. The branching ratio of $B_s\to D^0\bar D^0$ is about $6.8\times10^{-4}$, which could be measured in LHC-b. From the calculation, it could be found that this branching rat…
We give predictions for the branching ratios of several rare radiative B-decays which proceed only through weak annihilation mechanism. In addition to previous analysis we estimate the branching ratios of $\bar{B}^0_s\to D^{*0}γ$ and $B_c^-\toρ^-γ$ decays and obtain $2.87\cdot 10^{-9}$ and $2.59\cdot 10^{-7}$ for them correspondingly. The accuracy of the predictions is at the level of 20\%.
We calculate the branching ratios and CP asymmetries for B^0 to pi^+pi^-, B^+ to pi^+pi^0 and B^0 to pi^0pi^0 decays, in a perturbative QCD approach. In this approach, we calculate non-factorizable and annihilation type contributions, in addition to the usual factorizable contributions. We found that the annihilation diagram contributions are not very small as previous argument. Our result is in agreement with the measured branching ratio of B to pi^+pi^- by CLEO collaboration. With a non-negligible contribution from annihilation diagrams and a large strong phase, we predict a large direct CP …
The lighter top squark in supersymmetry can live long enough to form hadronic bound states if it has no kinematically allowed two-body decays that conserve flavor. In this case, scalar stoponium may be observable through its diphoton decay mode at the CERN Large Hadron Collider, enabling a uniquely precise measurement of the top-squark mass. The viability of the signal depends crucially on the branching ratio to diphotons. We compute the next-to-leading order QCD radiative corrections to stoponium annihilation decays to hadrons, photons, and Higgs scalar bosons. We find that the effect of thes…
We investigate the effect of unparticles in the pure annihilation type decays $B^- \to D_s^-ϕ$ and $ D_s^- K^{*0}$. Since these decays have only annihilation contributions their branching ratios are expected to be very small in the standard model and the direct CP asymmetry parameters to be zero. We find that due to the unparticle effect these branching ratios can be significantly enhanced from their standard model values. Furthermore, sizable nonzero direct CP violation could also be possible in these channels due to the presence of intrinsic CP conserving phase in the unparticle propagator.
With the perturbative QCD approach based on $k_T$ factorization, we study the pure annihilation type radiative decays $B^0 \to ϕγ$ and $B^0\to J/ψγ$. We find that the branching ratio of $B^0 \to ϕγ$ is $(2.7^{+0.3+1.2}_{-0.6-0.6})\times10^{-11}$, which is too small to be measured in the current $B$ factories of BaBar and Belle. The branching ratio of $B^0\to J/ψγ$ is $({4.5^{+0.6+0.7}_{-0.5-0.6}})\times10^{-7}$, which is just at the corner of being observable in the $B$ factories. A larger branching ratio $BR(B_s^0 \to J/ψγ) \simeq 5 \times 10^{-6}$ is also predicted. These decay modes will he…
The rare decays $B^+ \to D_s^{+} ϕ$, $B^0 \to D_s^{(*)-} K^+$ and $B^+ \to D_s^{(*)+} \bar{K}^0$ can occur only via annihilation type diagrams in the standard model. We calculate these decays in perturbative QCD approach. We found that the calculated branching ratio of $B^0 \to D_s^- K^+$ agree with the data which had been observed in the KEK and SLAC B factories. The decay $B^+ \to D_s^{(*)+} \bar K^0$ has a very small branching ratio at O ($10^{-8}$), due to the suppression from CKM matrix elements. The branching ratio of $B^+ \to D_s^+ ϕ$ is of order $10^{-7}$ which may be measured in the n…
We compute the cross section for the electromagnetic annihilation into charged leptons, and the electromagnetic scattering off nucleons, of spin-3/2 self-conjugate (Majorana) particles using the general form of the electromagnetic vertex function that was obtained previously for such particles. In addition to the restrictions imposed by common principles such as electromagnetic gauge invariance and hermiticity, the vertex function incorporates the restriction due to the Majorana condition as well as the particular properties related to the spinors in the Rarita-Schwinger representation, and is…
The rare decay $B^+ \to D_s^+ ϕ$ can occur only via annihilation type diagrams in the standard model. We calculate this decay in perturbative QCD approach with Sudakov resummation. We found that the branching ratio of $B^+ \to D_s^+ ϕ$ is of order $10^{-7}$ which may be measured in the near future by KEK and SLAC $B$ factories. The small branching ratio predicted in standard model makes this channel sensitive to new physics contributions.
In this paper, we calculate the branching ratio and direct CP asymmetry parameter of $B_c^{\pm}\to D^{0}K^{\pm}$ in the framework of perturbative QCD approach based on $k_T$ factorization. Besides the usual factorizable diagrams, both non-factorizable and annihilation type contributions are taken into account. We find that (a) the branching ratio is at the order of $10^{-5}$; (b) the tree annihilation diagrams and the penguin diagrams dominate the total contribution; and (c) the direct CP asymmetry is about 7%, which can be tested in the Large Hadron Collider beauty experiments (LHC-b) at CERN…
We analyzed the process of $B_s\rightarrow ρρ$ decay in QCD factorization (QCDF) and final state interaction (FSI) effects. In QCDF for this decay we have only the annihilation graph and we expected small Branching ratio. Then we considered FSI effect as a sizable correction where the intermediate states are $π^0π^0$, $π^+π^-$, $K^0\bar{K^0}$ and $K^+K^-$ mesons. To consider the amplitudes of these intermediate states, QCDF approach was used. The experimental branching ratio of $B_s\rightarrow ρρ$ is less than $3.20\times 10^{-4}$ and our result is $1.08 \times 10^{-9}$ and $3.29 \times10^{-4}…
The branching ratio for the rare two-body B_s -> rho gamma decay is calculated using the factorization assumption. This transition is dominated by the annihilation diagrams and, in principle, prone to receiving substantial contributions from new physics. We estimate Br(B_s -> rho gamma) = 1.6 x 10^-9 within the Standard Model and investigate the sensitivity of this decay mode to the effects of two new physics scenarios: vector quark model and supersymmetry. Our results indicate that the shift in branching ratio is at most around 10% with the addition of vector quarks and is negligibly small in…
In this work, we calculate the rare decays $B^0 \to D_s^{*-} K^+$ and $B^+ \to D_s^{*+} \bar{K}^0$ in perturbative QCD approach with Sudakov resummation. We give the branching ratio of $10^{-5}$ for $B^0 \to D_s^{*-}K^+$, which will be tested soon in $B$ factories. The decay $B^+ \to D_s^{*+} \bar{K}^0$ has a very small branching ratio at ${\cal O}(10^{-8})$, due to the suppression from CKM matrix elements $|V_{ub}^* V_{cd}|$. It may be sensitive to new physics contributions.
The rare decays $B_s^0\to D^\pm π^\mp$ and $\bar B_s^0\to D^\mp π^\pm$ can occur only via annihilation type diagrams in the standard model. In this paper, we calculate branching ratios of these decays in perturbative QCD approach ignoring soft final state interaction. From our calculation, we find that their branching ratios are at $\mathcal{O}(10^{-6})$ with large CP asymmetry, which may be measured in LHC-b experiment in future.
A conservative upper bound on the total dark matter (DM) annihilation rate can be obtained by constraining the appearance rate of the annihilation products which are hardest to detect. The production of neutrinos, via the process $χχ\to \barνν$, has thus been used to set a strong general bound on the dark matter annihilation rate. However, Standard Model radiative corrections to this process will inevitably produce photons which may be easier to detect. We present an explicit calculation of the branching ratios for the electroweak bremsstrahlung processes $χχ\to \barννZ$ and $χχ\to \barνe W$. …
In a class of low-energy supersymmetry models the photino is a natural dark matter candidate. We investigate the effects of post-freeze-out photino annihilations which can generate electromognetic cascades and lead to photo-destruction of $^4$He and subsequent overproduction of D and $^3$He. We also generalize our analysis to a generic dark matter component whose relic abundance is {\it not} determined by the cross section of the self-annihilations giving rise to electromagnetic showers.
We calculate, using unitarity, a lower bound on the branching ratio $χχ\to γγ$ and $χχ\to γZ$, where $χ$ is any halo dark matter particle that has $W^+W^-$ as one of the major annihilation modes. Examples of such particles are supersymmetric particles with a dominant Higgsino component, or heavy triplet neutrinos. A substantial branching ratio is found for the $γγ$ and $γZ$ modes. We estimate the strength of the monoenergetic $γ$ ray lines that result from such annihilations in the Galactic or LMC halos. (Latex file; 2 compressed uuencoded postscript figures available by anonymous ftp from van…
In this work, we calculate the {\it CP}-averaged branching ratios and the polarization fractions of the charmless hadronic $B_c \to A_2 A_3$ decays within the framework of perturbative QCD(pQCD) approach, where $A$ is either a light $^3P_1$ or $^1P_1$ axial-vector meson. These thirty two decay modes can occur through the annihilation topology only. Based on the perturbative calculations and phenomenological analysis, we find the following results: (a) the branching ratios of the considered thirty two $B_c\to A_2 A_3$ decays are in the range of $10^{-5}$ to $10^{-8}$; (b) $B_c\to a_1 b_1$, $\ov…
The continuum one-photon annihilation at psi(2S) in e+e- experiment is studied. Such contributions to the measured final state omega pi0 and pi+pi- at psi(2S) mass are estimated by phenomenological models. It is found that these contributions must be taken into account in the determination of branching ratios of psi(2S) --> omega pi0 and psi(2S) --> pi+ pi-, as well as other electromagnetic decay modes. The study reaches the conclusion that in order for BES to obtain the correct branching ratios on these decay modes, at least 10 inverse pb of data below the psi(2S) peak is needed.
Recently the branching ratios for $B^+\to K^+\bar K^0$ and $B^0 \to K^0 \bar K^0$ have been measured. Data indicate that the annihilation amplitudes in these decays are not zero. A non-zero annihilation amplitude plays an important role in CP violation for $B^+\to π^+ K^0, K^+ \bar K^0$. Using the measured branching ratios for these decays, we show that there is an absolute bound of 5% for the size of CP asymmetry in $B^+\to π^+ K^0$ from a relation between the amplitudes of these decays. The size of CP asymmetry in $B^+ \to K^+\bar K^0$ can, however, be as large as 90%. Future experimental da…
With the known branching ratios of psi(2S) to pi+pi- and psi(2S) to K+K-, the branching ratio of psi(2S) to K0short K0long is calculated as a function of the relative phase between the strong and the electromagnetic amplitudes of the psi(2S) decays. The study shows that the branching ratio of psi(2S) to K0short K0long is sensitive to the relative phase and a measurement of the K0short K0long branching ratio will shed light on the relative phase determination in psi(2S) to 0- 0- decays.
In the reaction of the antiproton-deuteron electromagnetic annihilation pbar + d --> e+e-n the value of the invariant mass M of the (e+e-) pair can be near or below the (pbar p) mass even for enough high momentum of incident antiproton. This allows to access the proton electromagnetic form factors in the time-like region of q^2 near the (pbar p) threshold. We estimate the cross section dsigma(pbar + d --> e+e-n)/dM for an antiproton beam momentum of 1.5 GeV/c. We find that near the (pbar p) threshold this cross section is about 1 pb/MeV. The case of heavy nuclei target is also discussed. Eleme…
Contrary to the reaction pbar + p --> e+ e- with a high momentum incident antiproton on a free target proton at rest, in which the invariant mass M of the (e+ e-) pair is necessarily much larger than the (pbar p) mass, in the reaction pbar + d --> n e+ e- the value of M can take values near or below the (pbar p) mass. In the antiproton-deuteron electromagnetic annihilation, this allows to access the proton electromagnetic form factors in the time-like region of q^2 near the (pbar p) threshold. We estimate the cross section dsigma(pbar +d --> e+ e- n)/dM for an antiproton beam momentum of 1.5 G…
By assuming that the scalar meson $K_0^*(1430)$ belongs to the first excited states or the lowest lying ground states, we study the pure annihilation-type decays $B \to K_0^{*\pm}(1430)K^{(*)\mp}$ in the QCD factorization approach. Within the standard model, the branching fractions are at the order of $10^{-8}-10^{-7}$, which is possible to be measured in the ongoing LHCb experiment or forthcoming Belle-II experiment. We also study these decays in the family non-universal $Z^\prime$ model. The results show that if $m_{Z^\prime}\approx 600\mathrm{GeV}$ ($ζ=0.02$), both the branching fractions a…
We study charmless pure annihilation type radiative B decays within the QCD factorization approach. After adding the vertex corrections to the naive factorization approach, we find that the branching ratios of $\bar{B}^0_d\toϕγ$, $\bar{B}^0_s\toρ^0γ$ and $\bar{B}^0_s\toωγ$ within the standard model are at the order of $\mathcal{O}(10^{-12})$, $\mathcal{O}(10^{-10})$ and $\mathcal{O}(10^{-11})$, respectively. The smallness of these decays in the standard model makes them sensitive probes of flavor physics beyond the standard model. To explore their physics potential, we have estimated the contr…
In this work, within the QCD factorization approach, we investigate the branching fractions and CP asymmetries of decays $B \to K_0^*(1430)ρ$ and $B \to K_0^*(1430)ϕ$ under two different scenarios both in the standard model and the family nonuniversal $Z^\prime$ model. We find that the annihilation terms play crucial roles in these decays and lead to the main uncertainties. For decays $B^- \to \bar K_0^{*-} (1430)ρ^0 (ω)$, the new $Z^\prime$ boson could change branching fractions remarkably. However, for other decays, its contribution might be clouded by large uncertainties from annihilations.…
We study the large-order asymptotic behavior of the perturbation series for short-distance coefficients in the NRQCD factorization formulas for the decays J/psi --> e^+e^- and eta_c --> gamma gamma. The short-distance coefficients of the leading matrix elements are calculated to all orders in the large-N_f limit. We find that there is a universal Borel resummable renormalon associated with the cancellation of the Coulomb singularity in the short-distance coefficients. We verify that the ambiguities in the short-distance coefficients from the first infrared renormalon are canceled by ambiguitie…
The two-body mesonic $B$ decays induced only via a single $W$-exchange or annihilation quark diagram, such as $B^-_u\rightarrow D^{(*)-}_sK^{(*)0}$ and $\bar{B}^0_d\rightarrow D^{(*)+}_sK^{(*)-}$, are analyzed in the factorization approximation. We estimate the branching ratios for those transitions into two pseudoscalar mesons, and find them to be negligibly small. The significant effect of final-state rescattering is illustrated by taking $B^-_u\rightarrow D^-\bar{K}^0$ for example.
We estimate the electromagnetic decay rates of $χ_{c0}\rightarrow γγ$ and $χ_{c2}\rightarrowγγ$ by taking into account both relativistic and QCD radiative corrections. The decay rates are derived in the Bethe-Salpeter formalism and the QCD radiative corrections are included in accordance with factorization assumption. Using a QCD-inspired interquark potential, we obtain relativistic BS wavefunctions of $χ_{c0}$ and $χ_{c2}$ by solving BS equations for the corresponding $^{2S+1}L_J$ states. Our numerical result for the ratio $R=\frac{Γ(χ_{c0}\rightarrowγγ)}{Γ(χ_{c2} \rightarrowγγ)}$ is about $1…
Energy injected into the Cosmic Microwave Background at redshifts z<10^6 will distort its spectrum permanently. In this paper we discuss the distortion caused by annihilations of relic particles. We use the observational bounds on deviations from a Planck spectrum to constrain a combination of annihilation cross section, mass, and abundance. For particles with (s-wave) annihilation cross section, <σ|v|>=σ_0, the bound is f[(σ_0/6e-27cm^3/s)(Ω_{X\bar{X}}h^2)^2]/(m_X/MeV)<0.2, where m_X is the particle mass, Ω_{X\bar{X}} is the fraction of the critical density the particle and its antiparticle c…
A self-consistent global fitting method based on the Markov Chain Monte Carlo technique to study the dark matter (DM) property associated with the cosmic ray electron/positron excesses was developed in our previous work. In this work we further improve the previous study to include the hadronic branching ratio of DM annihilation/decay. The PAMELA $\bar{p}/p$ data are employed to constrain the hadronic branching ratio. We find that the 95% ($2σ$) upper limits of the quark branching ratio allowed by the PAMELA $\bar{p}/p$ data is $\sim 0.032$ for DM annihilation and $\sim 0.044$ for DM decay res…
We study the rare decays $B^+ \to D^{(*)+}K^{(*)0}$, which can occur only via annihilation type diagrams in the standard model. We calculate all of the four modes, $B \to PP, VP, PV, VV$, in the framework of perturbative QCD approach and give the branching ratios of the order about $10^{-6}$.
We consider regions of the parameter space of the Minimal Supersymmetric Standard Model (MSSM) with bino-like neutralino dark matter in which a large fraction of the total dark matter annihilation cross section in the present era arises from annihilation to final states with monoenergetic photons. The region of interest is characterized by light sleptons and heavy squarks. We find that it is possible for the branching fraction to final states with monoenergetic photons to be comparable to that for continuum photons, but in those cases the total cross section will be so small that it is unlikel…
Spherical gravitational collapse of a cold gas of annihilating particles involves a competition between the free-fall rate $\propto\sqrtρ$ and the (s-wave) annihilation rate $\proptoρ$. Thus, there is a critical density $\rhoann$ above which annihilation proceeds faster than free fall. Gravitational collapse of a cloud of (initial) mass $M$ to a black hole is only possible if $3/32πG^3M^2\lesssim\rhoann$, or $M\gtrsim\Mann\equiv (3/32πG^3\rhoann)^{1/2}$. For a particle mass $m$ and freeze-out temperature $T_f=m/x_f$, the minimum black hole mass is $\Mann\approx 10^{10}\msun \times(x_f\sqrt{g_\…
Heavy-hadron chiral perturbation theory (HH$χ$PT) is applied to the decays of the even-parity charmed strange mesons, D_{s0}(2317) and D_{s1}(2460). Heavy-quark spin symmetry predicts the branching fractions for the three electromagnetic decays of these states to the ground states D_s and D_s^* in terms of a single parameter. The resulting predictions for two of the branching fractions are significantly higher than current upper limits from the CLEO experiment. Leading corrections to the branching ratios from chiral loop diagrams and spin-symmetry violating operators in the HH$χ$PT Lagrangian …
We study the {\it CP}-averaged branching fractions and the {\it CP}-violating asymmetries in the pure annihilation decays of $B_s^0 \to a_0^+ a_0^-$ and $B_d^0 \to K_0^{*+} K_0^{*-}$, where $a_0\;[K_0^*]$ denotes the scalar $a_0(980)$ and $a_0(1450)$ [$K_0^*(800) ( {\rm or}\; κ)$ and $K_0^*(1430)$], with the perturbative QCD factorization approach under the assumption of two-quark structure for the $a_0$ and $K_0^*$ states. The numerical results show that the branching ratios of the $B_d^0 \to K_0^{*+} K_0^{*-}$ decays are in the order of $10^{-6}$, while the decay rates of the $B_s^0 \to a_0^…
We study the possible indirect neutrino signal from dark matter annihilations inside the solar interior for relatively light dark matter masses in the O(10) GeV range. Due to their excellent energy reconstruction capabilities, we focus on the detection of this flux in liquid argon or magnetized iron calorimeter detectors, proposed for the next generation of far detectors of neutrino oscillation experiments and neutrino telescopes. The aim of the study is to probe the ability of these detectors to determine fundamental properties of the dark matter nature such as its mass or its relative annihi…
The rare decays $B^0 \to D_s^- K^+$ and $B^+ \to D_s^+ \bar{K}^0$ can occur only via annihilation type diagrams in the standard model. We calculate these decays in perturbative QCD approach. We found that the calculated branching ratio of $B^0 \to D_s^- K^+$ agreed with the data which had been observed in the KEK and SLAC $B$ factories. While the decay $B^+ \to D_s^+ \bar{K}^0$ has a very small branching ratio at ${\cal O}(10^{-8})$, due to the suppression from CKM matrix elements $|V_{ub}^* V_{cd}|$.
The mixing between nonstrange and strange quark wavefunctions in the $ω$ and $ϕ$ mesons leads to a small predicted branching ratio $\b(D_s^+ \to ωe^+ ν_e) = {\cal O}(10^{-4})(δ/3.34^\circ)^2$, where $δ$ is the mixing angle. The value $δ= -3.34^\circ$ is obtained in a mass-independent analysis, while a mass-dependent analysis gives $δ= -0.45^\circ$ at $m(ω)$ and $-4.64^\circ$ at $m(ϕ)$. Measurement of this branching ratio thus can tell whether the decay is dominated by $ϕ$--$ω$ mixing, or additional nonperturbative processes commonly known as "weak annihilation" (WA) contribute. The role of WA …
Experimental data suggest the existence of a minimal length scale in annihilation process for the reaction e+e- --> gamma gamma (gamma). Nonlinear electrodynamics coupled to gravity and satisfying the weak energy condition predicts, for an arbitrary gauge invariant lagrangian, the existence of a spinning charged electromagnetic soliton asymptotically Kerr-Newman for a distant observer with a gyromagnetic ratio g=2. Its internal structure includes an equatorial disk of de Sitter vacuum which has properties of a perfect conductor and ideal diamagnetic, and displays superconducting behavior withi…
In this paper, we study nonleptonic charmless B decays to two light pseudoscalar mesons within the frame of QCD factorization, including the contributions from the chirally enhanced power corrections and weak annihilation. Predictions for the CP-averaged branching ratios and CP-violating asymmetries are given. Within the reasonable range of the parameters, we find that our predictions for the branching ratios of B -> PP are consistent with the present experimental data. But because of the logarithmic divergences at the endpoints in the hard spectator scatterings and weak annihilation, there ar…
The electromagnetic radiation by quark-gluon plasma in strong magnetic field is calculated. The contributing processes are synchrotron radiation and one--photon annihilation. It is shown that in relativistic heavy--ion collisions at RHIC and LHC synchrotron radiation dominates over the annihilation. Moreover, it constitutes a significant part of all photons produced by the plasma at low transverse momenta; its magnitude depends on the plasma temperature and the magnetic field strength. Electromagnetic radiation in magnetic field is probably the missing piece that resolves a discrepancy between…
The CLAS detector was used to obtain the first ever measurement of the electromagnetic decay of the $Σ^{*+}(1385)$ from the reaction $γp \to K^0 Σ^{*+}(1385)$. A real photon beam with a maximum energy of 3.8 GeV was incident on a liquid-hydrogen target, resulting in the photoproduction of the kaon and $Σ^*$ hyperon. Kinematic fitting was used to separate the reaction channel from the background processes. The fitting algorithm exploited a new method to kinematically fit neutrons in the CLAS detector, leading to the partial width measurement of $250.0\pm56.9(stat)^{+34.3}_{-41.2}(sys)$ keV. A U…
An upper limit on the total annihilation cross section of dark matter (DM) has recently been derived from the observed atmospheric neutrino background. We show that comparable bounds are obtained for DM masses around the TeV scale by observations of the diffuse gamma-ray flux by EGRET, because electroweak bremsstrahlung leads to non-negligible electromagnetic branching ratios, even if DM particles only couple to neutrinos at tree level. A better mapping and the partial resolution of the diffuse gamma-ray background into astrophysical sources by the GLAST satellite will improve this bound in th…
We have computed the branching ratios of the exclusive pseudoscalar (vector) + tensor modes that are allowed in the decays of the B_c meson. The dominant spectator and annihilation contributions in those decays are evaluated using the factorization hypothesis. We find that some of these decay channels, such as B_c --> (ρ^-, D_s^{*-}, D_s^{-})χ_{c2} and B_c^ -->π^- \bar{B_{s2}^{*0}}, have branching ratios of the order of 10^{-4}, which seems to be at the reach of forthcoming experiments at the LHC. The inclusive branching fraction of the two-body B_c decays involving tensor particles is approxi…
In the standard model the two-body charmless hadronic $B_c$ meson decays can occur via annihilation diagrams only. In this work, we studied the $B_c \to PP, PV/VP,VV$ decays by employing the perturbative QCD (pQCD) factorization approach. From our calculations, we find that (a) the pQCD predictions for the branching ratios of the considered $B_c$ decays are in the range of $10^{-6}$ to $10^{-8}$; (b) for $B_c \to PV/VP, VV$ decays, the branching ratios of $ΔS= 0$ decays are much larger than those of $ΔS =1$ ones because the different Cabibbo-Kobayashi-Maskawa(CKM) factors are involved; (c) ana…
We investigate the radiative $B_{c} \to D_{s1} γ$ transition in the framework of QCD sum rules. In particular, we calculate the transition form factors responsible for this decay in both weak annihilation and electromagnetic penguin channels using the quark condensate, mixed and two-gluon condensate diagrams as well as propagation of the soft quark in the electromagnetic field as non-perturbative corrections. These form factors are then used to estimate the branching ratios of the channels under consideration. The total branching ratio of the $B_{c} \to D_{s1} γ$ transition is obtained to be i…
In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study the annihilation channel in antiproton nucleon collisions with production of a single charged or neutral pion and a lepton-antilepton pair. These reactions allow to access nucleon and axial electromagnetic form factors in time-like region and offer a unique possibility to study the kinematical region below two nucleon threshold. The differential cross section in an experimental set-up where the pion is fully detected is given with explicit dependence on the relevant nucleon form factors. The possibility …
We calculate the branching ratios of pure annihilation type decays $B^0\rightarrow D_{s}^{-}K_{2}^{*+}$ and $B_s\rightarrow \bar{D}a_{2}$ using the perturbative QCD approach based on $k_T$ factorization. The branching ratios are predicted to be $(60.6_{-16.5\,-10.4\,-2.1}^{+17.3\,+4.3\,+3.2}) \times 10^{-6}$ for $B^0\rightarrow D_{s}^{-}K_{2}^{*+}$, $(1.1_{-0.4\,-0.2\,-0.1}^{+0.4\,+0.1\,+0.1})\times 10^{-6}$ for $B_s\rightarrow \bar{D}a_{2}^{0}$ and $(2.3_{-0.8\,-0.4\,-0.1}^{+0.8\,+0.2\,+0.1})\times 10^{-6}$ for $B_{s}\rightarrow D^{-}a_{2}^{+}$. They are large enough to be measured in the ong…
Based on the S-matrix approach, we introduce a modified formula for the $π^{\pm}$ electromagnetic form factor which describes very well the experimental data in the energy region $2m_π \leq \sqrt{s} \leq 1.1$ GeV. Using the CVC hypothesis we predict $B(\tpp) = (24.75 \pm 0.38)\% $, in excellent agreement with recent experiments.
The precision measurements of the cosmic microwave background power spectrum put a strong constraint on the dark matter annihilation cross section since the electromagnetic energy injection by the dark matter annihilation affects the ionization history of the universe. In this paper, we update our previous simulation code for calculating the ionization history with the effect of dark matter annihilation by including Helium interactions and improving the precision of calculations. We give an updated constraint on the annihilation cross section and mass of dark matter using the modified RECFAST …
We study the fluxes of neutrinos from annihilations of dark matter particles in the Sun and the Earth. We give the spectra of all neutrino flavors for the main known annihilation channels: nu-antinu, b-bbar, tau-taubar, c-cbar, light quarks, ZZ, W^+W^-. We present the appropriate formalism for computing the combined effect of oscillations, absorptions, nu_tau-regeneration. Total rates are modified by an O(0.1--10) factor, comparable to astrophysical uncertainties, that instead negligibly affect the spectra. We then calculate different signal topologies in neutrino telescopes: through-going muo…
It was recently argued by Hooper and Goodenough [arXiv:1010.2752] that the excess gamma ray emission from within 1-2 degrees of the galactic center can be well-described by annihilation of ~8 GeV dark matter particles into tau pairs. I show that such a dark matter signal can be obtained naturally in the lepton-specific two-Higgs-doublet model extended by a stable singlet scalar dark matter candidate. The favored parameter region prefers a light Higgs state (below 200 GeV) with enhanced couplings to leptons and sizable invisible branching fraction. Part of the favored region leads to invisible …
