Kunio Kaneta, Yann Mambrini, Keith A. Olive
We compare dark matter production from the thermal bath in the early universe with its direct production through the decay of the inflaton. We show that even if dark matter does not possess a direct coupling with the inflaton, Standard Model loop processes may be sufficient to generate the correct relic abundance.
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Muon pair production in exclusive radiative decays $χ_{cJ}\to J/ψμμ$, $χ_{bJ}\toΥμμ$ are considered. We present numerical values of the branching fractions and distributions over various kinematical variables.
Some results of a calculation of electroweak radiative corrections to $W$ and $Z$ boson production in hadronic collisions are presented.
We present the radiative corrections to off-shell $W$-pair production, as calculated within the double-pole approximation.
QED radiative effects are considered in the case of measurement of spin-density matrix elements of diffractive $ρ$-meson electroproduction. Large radiative correction for $r^5_{00}$ is found in the kinematics of collider experiments at HERA.
We briefly describe the RacoonWW approach to calculate radiative corrections to e+ e- -> W W -> 4 fermions and present numerical results for the total W-pair production cross section at LEP2.
We study the impact of beam polarization on radiative neutralino production e+e- \to χ^0_1 χ^0_1 photon at the International Linear Collider. We show that longitudinal polarized beams significantly enhance the signal and simultaneously reduce the Standard Model background from radiative neutrino production e+e- \to ν\barνphoton. We point out that the radiative production of neutralinos could be the only accessible SUSY particles, if neutralinos, charginos, sleptons, as well as squarks and gluinos are too heavy to be pair-produced in the first stage of the ILC at sqrt{s} = 500 GeV.
We present some results of a new calculation of the O(alpha) electroweak radiative corrections to W boson production at hadron colliders with special emphasis on the transverse mass distribution.
We show that radiative corrections to chargino production in electron-positron annihilation with polarized beams can be large especially in the case of right handed electrons. In addition, there is some dependency on the squark masses that allows us to extract information about the squark spectrum from the chargino production.
We give an overview of the problems and developments associated with the calculation of radiative corrections to off-shell gauge-boson pair production in e^+ e^- collisions.
The status of precision calculations for the processes e+e- --> WW --> 4 fermions is reviewed, paying particular attention to questions of gauge invariance and recent progress concerning photonic radiative corrections.
Radiative W production at hadron colliders is an important testing ground for the Standard Model. We consider W gamma gamma production which is sensitive to the quartic WW gamma gamma coupling. Furthermore the Standard Model amplitude for this process contains a radiation zero. We present a calculation of the NLO QCD corrections for W gamma gamma production at the LHC.
We present a \lq\lq theorem" which quantifies, for inclusive processes, the level of suppression of the radiative interference effects between the production and decay stages of heavy {\it unstable} particles. The theorem, which is based on very general physical arguments, is applicable to all orders in the coupling.
We calculate the strong radiative corrections to the process p pbar -> W(->e nu) g^*(->b bbar). At the Tevatron this process is the largest background to the associated Higgs boson production p pbar -> W(-> e nu) H(-> b bbar). The calculation is based on the subtraction procedure, and the corrections are found to be significant.
We discuss the O(alpha) electroweak radiative corrections to W boson production at the Tevatron and their effect on the W boson mass extracted by experiment. The results of a new calculation of the O(alpha) corrections are presented and compared with those of a previous calculation. We also briefly discuss the O(alpha) corrections to Z boson production at the Tevatron and two-photon radiation in W and Z events.
Radiative Corrections to $W$ Pair Production and effects of finite width of the $W$ bosons are studied using the Monte Carlo {\tt WOPPER}. As an example the influence of QED radiative corrections on the reconstruction of the $W$ helicities at LEP 200 and a future 500 GeV $e^+ e^-$ collider is discussed.
Process of muon (pion) pair production with small invariant mass in the electron-positron high-energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Dell-Yan picture for differential cross section is valid in the charge-even experimental set-up. Radiative corrections both for electron block and for final state block are taken into account.
O(α) QED radiative corrections to neutral current deep inelastic production of heavy quarks are calculated in the leading log approximation and compared with the corresponding corrections assuming a massless charm parton. Besides the inclusive case, corrections to the semi-inclusive d^3σ/dx dy dz and the effect of z-cuts are studied. In the latter case, the massless corrections differ from the correct massive radiative corrections to deep inelastic heavy quark production by about 40%-10% for 0.2\lesssim z \lesssim 0.5.
Using a bound-state model of weakly bound gluons for glueballs made of two gluons and a natural generalization of the perturbative QCD formalism for exclusive hadronic processes, we present results for glueball production in radiative J/psi, Upsilon decays into several possible glueball states, including L \not= 0 ones. We perform a detailed phenomenological analysis, presenting results for the more favored experimental candidates and for decay angular distributions.
We report on the effect that one-loop radiative corrections to the chargino pair production cross section has on the determination of the fundamental parameters of the theory. We work in the context of electron-positron colliders with sqrt(s)=500 GeV. We conclude that the inclusion of these corrections is crucial in precision measurements, specially at large and small values of tan(beta).
An alternative calculation of the lowest order electroweak radiative corrections to the single W-boson production in hadron-hadron collision in the framework of the quark parton model without any absorption of the collinear quark singularity into the parton distributions is carried out. Numerical analysis under Tevatron and LHC kinematic conditions is performed.
We study the production of the lightest neutralinos in the radiative process $e^+e^- \to \tildeχ^0_1 \tildeχ^0_1γ$ in low energy supersymmetric models for the International Linear Collider energies with longitudinally polarized electron and positron beams. For this purpose we consider the case of nonminimal supersymmetric standard model as well as the case of minimal supersymmetric standard model. At the first stage of a linear collider, with $\sqrt{s} =500$ GeV, the radiative production of the lightest neutralinos may be a viable channel to study supersymmetric partners of the Standard Model …
We study radiative neutralino production e^+e^- \to \tildeχ^0_1 \tildeχ^0_1γat the linear collider with longitudinally polarised beams. We consider the Standard Model background from radiative neutrino production e^+e^- \to ν\barνγ, and the supersymmetric radiative production of sneutrinos e^+e^- \to \tildeν\tildeν^\ast γ, which can be a background for invisible sneutrino decays. We give the complete tree-level formulas for the amplitudes and matrix elements squared. In the Minimal Supersymmetric Standard Model, we study the dependence of the cross sections on the beam polarisations, on the pa…
Higgs boson mass sum rules of supersymmetric models offer attractive targets for precision tests at future muon colliders. These sum rules involve the gauge boson masses as well as the masses of the Higgs boson states which can be precisely measured in the $s$-channel production process at a muon collider. These measurements can sensitively probe radiative corrections to the Higgs boson masses as well as test for CP-violation and nonminimality of the Higgs sector.
We study the production of the lightest neutralinos in the radiative process $e^+e^- \to \tildeχ^0_1 \tildeχ^0_1γ$ in supersymmetric models with grand unification. We consider models wherein the standard model gauge group $SU(3)_c \times SU(2)_L \times U(1)_Y$ is unified into the grand unified gauge groups SU(5), or SO(10). We study this process at energies that may be accessible at a future International Linear Collider. We compare and contrast the dependence of the signal cross section on the grand unified gauge group, and different representations of the grand unified gauge group, into whic…
Contributions from the reaction e+e- --> pi+pi- e+e- to the pion form factor measurement via radiative return method are discussed basing on the results of a Monte Carlo generator (EKHARA). The generator contains contributions from the initial and final state emission of a e+e- pair from e+e- --> pi+pi- production diagrams and the pi+pi- pair production from space-like and time-like Bhabha diagrams. A detailed study is performed for the Phi- factory energy. Tests of the generation procedure are also presented.
We report on QCD radiative corrections to the process, p\bar{p} to Zb\bar{b} in the approximation in which the b-quark is considered massless. The implementation of this process in the general purpose Monte Carlo program MCFM is discussed in some detail. These results are used to investigate backgrounds to Higgs boson production in the ZH channel. We investigate the Higgs mass range (100 GeV < m_H < 130 GeV) for the Tevatron running at sqrt{s}=2 TeV.
For the envisioned high precision measurement of the W boson mass at the Tevatron and LHC it is crucial that the theoretical predictions for the W and Z production processes are under control. We briefly summarize the status of the electroweak radiative corrections to p p(pbar) -> W -> l nu and p p(pbar) -> Z,gamma -> l+ l- (l=e,mu), and present some numerical results.
We compute the next-to-leading order corrections in $α_s$ to prompt diphoton production in association with a jet at hadron colliders. We use a next-to-leading order general-purpose partonic Monte Carlo event generator that allows the computation of a rate differential in the produced photons and hadrons.
The process of the muon (pion) pair production with small invariant mass in the electron--positron high--energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Drell--Yan picture for differential cross section is valid in the charge--even experimental set--up. Radiative corrections both for electron block and for final state block are taken into account.
Large scale calculation for the radiative corrections required for the current and future collider experiments can be done automatically using the GRACE-LOOP system. Here several results for e+e- --> 3-body processes are presented including e+e- --> e+e-H and e+e- --> nu nubar gamma.
We present the LL final state radiative effects for the exact O(alpha) YFS exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte Carlo event generator methods. The respective event generator, version 1.12 of the program YFSWW3, wherein both Standard Model and anomalous triple gauge boson couplings are allowed, generates n(γ) radiation both from the initial state and from the intermediate W+ W- and generates the LL final state W decay radiative effects. Sample Monte Carlo data are illustrated.
Radiative corrections to gauge boson and Higgs production computed recently using soft-collinear effective theory (SCET) require the one-loop high-scale matching coefficients in the standard model. We give explicit expressions for the matching coefficients for the effective field theory (EFT) operators for q qbar -> VV and q qbar -> phi^+ phi for a general gauge theory with an arbitrary number of gauge groups. The group theory factors are given explicitly for the standard model, including both QCD and electroweak corrections.
We study one loop electroweak corrections to the production of a pair of charged Higgs bosons through an intermediate $Z$-boson or photon. In particular, we consider the effects of graphs with top and bottom quarks and squarks in the loop within the context of the Minimal Supersymmetric Model. We find that the corrections can be considerable, and typically are of the order of 10\% to 20\%.
Muon pair production through the radiative return is of importance for a measurement of the hadronic production cross section in two ways: it provides an independent calibration and it may give rise to an important background for a measurement of the pion form factor. With this motivation the Monte Carlo event generator PHOKHARA is extended to include next-to-leading order radiative corrections to the reaction $e^+e^-\to μ^+μ^-γ$. Furthermore, virtual ISR corrections to FSR from pions are introduced, which extends the applicability of the generator into a new kinematical regime. Finally, the e…
The O(α) electroweak radiative corrections to the process pp, ppbar\to W \to\ell^\pmν(\ell=e,μ) are calculated. The O(α) corrections can be decomposed into separately gauge invariant contributions to the W boson production and decay processes. Factorizing the collinear singularity associated with initial state photon radiation into the parton distribution functions, we find that initial state corrections have a significantly smaller effect than final state radiative corrections. We study in detail the effect of electroweak radiative corrections on a number of interesting observables: the W tra…
Electroweak one-loop radiative corrections to the process e^+ e^- -> t tbar are revisited. Two groups from Karlsruhe and Bielefeld/Zeuthen performed independent calculations of both (virtual and soft) QED contributions and weak virtual corrections. For the angular distribution an agreement of at least eight digits for the weak corrections and of at least seven digits for additional photonic corrections is established.
We study how the scalar f_0(980) and a_0(980) states are produced in the two-photon collisions and radiative decays of the phi meson through unitarized Born amplitudes with the charged pion and kaon loops followed by S-wave meson-meson scattering amplitudes. We found in a previous paper that f_0(980) is generated as the bound state resonance, but a_0(980) as the cusp, and find herre that the nature of the generation of both states is consistent with the features of the production processes.
We analyze the impact of electron and positron beam polarization on radiative neutralino production at the International Linear Collider (ILC). We focus on three different mSUGRA scenarios in turn at the Higgs strahlung threshold, the top pair production threshold, and at $\sqrt{s} =500\GeV$. In these scenarios at the corresponding $\sqrt{s}$, radiative neutralino production is the only supersymmetric production mechanism which is kinematically allowed. The heavier neutralinos, and charginos as well as the sleptons, squarks and gluinos are too heavy to be pair produced. We calculate the signal…
We apply the newly developed NRQCD factorization formula to analyze the exclusive production of the fully-charmed tetraquark $T_{4c}$ plus a hard photon at $B$ factory. For simplicity, in this work we have concentrated on the associated production of the $0^{++}$ and $2^{++}$ tetraquarks with a photon. With some rough estimates about the size of the unknown nonperturbative NRQCD matrix elements, we predict the production rates of these types of exclusive channels at $\sqrt{s}=10.6$ GeV and also assess their observation prospect at {\tt Belle 2} experiment.
We study the production of the lightest neutralinos in the radiative process $e^+e^- \to \tildeχ^0_1 \tildeχ^0_1γ$ in low energy supersymmetric models for the International Linear Collider energies. This includes the minimal supersymmetric standard model as well as its extension with an additional chiral Higgs singlet superfield, the nonminimal supersymmetric standard model. We compare and contrast the dependence of the signal cross section on the parameters of the neutralino sector of the minimal and nonminimal supersymmetric standard model. We also consider the background to this process com…
The effect of virtual electroweak corrections to $e^+e^- \rightarrow t \bar{t}$ and the contribution of the radiation processes $e^+e^- \rightarrow t\bar{t}Z, t\bar{t}H$ to the inclusive top pair production cross section and forward-backward asymmetry are discussed in the high energy regime.
We study the production of the lightest neutralinos in the process $e^+ e^- \rightarrow χ_1^0 χ_1^0 γ$ in supersymmetric grand unified models for the International Linear Collider Energies with longitudinally polarized beams. We consider cases where the standard model gauge group is unified into the grand unified gauge groups SU(5), or SO(10). We have carried out a comprehensive study of this process in the SU(5) and SO(10) grand unified theories which includes the QED radiative corrections. We compare and contrast the dependence of the signal cross section on the grand unified gauge group, an…
One-loop radiative corrections to the production cross section of a pair of light charginos in e+e- colliders are calculated within the MSSM. Top and bottom quarks and squarks are considered in the loops, and they are renormalized using the MS-bar scheme. If the center of mass energy is equal to 192 GeV, positive corrections typically of 10% to 15% are found when the squark mass parameters are equal to 1 TeV.
Processes of electron-positron annihilation into charged pions and kaons are considered. Radiative corrections are taken into account exactly in the first order and within the leading logarithmic approximation in higher orders. A combined approach for accounting exact calculations and electron structure functions is used. An accuracy of the calculation can be estimated about 0.2%.
The presented paper is devoted to theoretical analysis of charmonium mesons $η_c$, $J/ψ$, $χ_{c0,1,2}$, and $h_c$ production in exclusive radiative $Z$ boson decays in the frameworks of Nonrelativistic Chromodynamic and amplitude expansion on the light-cone. In the framework of light-cone expansion amplitudes and widths of all processes are described with one universal relation. It is interesting to note that from this relation it follows automatically which component of $Z$ boson (either vector or axial) gives contribution to the width of the particular decay. It is shown that the effect of i…
The lowest order radiative correction to the differential cross-section of process of muon pair production with emission of hard photon at high energy electron-positron annihilation are calculated. Taking into account the emission of additional soft and hard photon the cross-section can be put in the form of Drell-Yan process in leading logarithmical approximation. Applying the crossing transformation we obtain the cross section of radiative electron-muon high-energy scattering process. Virtual and soft photon emission contributions of non-leading form are tabulated for several typical kinemat…
We calculate the MSSM $O(α)$ corrections to the main production processes of strong top pair production at the upgraded Tevatron and at the LHC. In exploring the potential of future hadron colliders for performing electroweak precision physics we study their effects on the total hadronic cross sections, the invariant $t\bar t$ mass distributions and give first results for parity violating asymmetries in the production of left and right handed top quarks.
The results of a complete one-loop calculation for the production of chargino pairs in electron-positron collisions, including the option of polarized beams, are presented. The calculation has been performed in the on-shell renormalization scheme. Applications to the integrated cross section, to the forward-backward asymmetry for unpolarized beams, and to the left-right asymmetry show that the higher-order effects have a sizeable influence on the theoretical predictions and therefore should be properly taken into account for detailed studies in the MSSM.
We present the full ${\cal O}(α_{ew})$ electroweak radiative corrections to the Higgs-boson production in association with $Z^0$-boson pair at an electron-positron linear collider(LC) in the standard model. We analyze the dependence of the full one-loop corrections on the Higgs-boson mass $m_{H}$ and colliding energy $\sqrt{s}$. We find that the corrections significantly suppress the Born cross section, and the ${\cal O}(α_{ew})$ electroweak radiative corrections are generally between 1.0% and -15% in our chosen parameter space, which should be taken into consideration in the future precise ex…
A parton shower method for the photonic radiative correction is applied to the single W-boson production processes. The energy scale for the evolution of the parton shower is determined so that the correct soft-photon emission is reproduced. Photon spectra radiated from the partons are compared with those from the exact matrix elements, and show a good agreement. Possible errors due to a inappropriate energy-scale selection or due to the ambiguity of energy scale determination are also discussed, particularly for the measurements on triple gauge-couplings.
We study radiative corrections to chargino production at linear colliders with polarised electron beams. We calculate the one-loop corrected cross-sections for polarised electon beams due to three families of quarks and squarks, working in the $\bar{MS}$ scheme, extending our previous calculation of the unpolarised cross-section with one-loop corrections due to the third family of quarks and squarks. In some cases we find rather large corrections to the tree-level cross-sections. For example for the case of right-handed polarised electrons and large $\tan β$ the corrections can be of order 30%…
We present the contributions from all types of one-loop corrections to the scattering amplitude for the pair production of polarized charginos or neutralinos from polarized electron-positron annihilation. The contributions are classified in terms of ``prototypes'' distinguished by the number of particles inside the loops and their spins. The results are quoted in terms of the Veltman-Passarino functions in terms of general couplings and internal masses. The results can therefore be applied to any supersymmetric extension of the Standard Model or indeed to any polarized fermion pair production …
This paper presents the high-precision theoretical predictions for $e^+e^- \to l^-l^+$ scattering. Calculations are performed using the {\tt SANC} system. They take into account complete one-loop electroweak radiative corrections as well as longitudinal polarization of initial beams. Reaction observables are obtained using the helicity amplitude method with taking into account initial and final state fermion masses. Numerical results are given for the center-of-mass energy range $\sqrt{s}=250-1000$ GeV with various degrees of polarization.
The naive implementation of finite width effects in processes involving unstable particles can violate gauge invariance. For the example of radiative $W$ production and decay, $q\bar q' \to \ellνγ$, at tree level, it is demonstrated how gauge invariance is restored by including the imaginary part of triangle graphs in addition to resumming the imaginary contributions to the $W$ vacuum polarization. Monte Carlo results are presented for the Fermilab Tevatron.
If in a supersymmetric model, the lightest chargino is nearly degenerate with the lightest neutralino, the former can decay into the latter alongwith a soft pion (or a lepton-neutrino pair). Near degeneracy of the chargino and neutralino masses can cause the other decay products (the pion or the lepton) to be almost invisible. Photon-photon colliders offer a possibility of clean detection of such an event through a hard photon tag.
We demonstrate that the results of the complete first order calculation of the non-factorizable QED corrections to the single-inclusive cross-sections for $e^+e^- \to W^+W^- \to 4$ fermions could be very well reproduced by a simple physically motivated ansatz. The latter allows to take into account effectively the screening role of the non-Coulomb radiative mechanisms by introducing a dampening factor in front of the width-dependent part of the known first-order Coulomb correction, the so-called screened-Coulomb ansatz.
The full $\mathcal{O}(α)$ electroweak radiative corrections to $t \bar{t} γ$ and $e^-e^+γ$ productions at the International Linear Collider (ILC) are presented in this paper. The computation is performed with the help of GRACE-Loop system. In the physical results, we discuss on the cross section, electroweak corrections, and the top quark forward-backward asymmetry ($A_{FB}$) which are the function of the center-of-mass energy.
For energies relevant to future linear colliders, \sqrt{s} >~ 500 GeV, the WW fusion channel dominates the Higgs boson production cross section e+e- -> \barννh^0. We have calculated the one-loop corrections to this process due to fermion and sfermion loops in the context of the MSSM. As a special case, the contribution of the fermion loops in the SM has also been studied. In general, the correction is negative and sizeable of the order of 10%, the bulk of it being due to fermion loops.
Radiative corrections to processes that involve the production and subsequent decay of unstable particles are complex due to various theoretical and practical problems. The so-called double-pole approximation offers a way out of these problems. This method is applied to the reaction $e^{+}e^{-} \to W^{+}W^{-} \to 4 $fermions, which allows us to address all the key issues of dealing with unstable particles, like gauge invariance, interactions between different stages of the reaction, and overlapping resonances. Within the double-pole approximation the complete $\OO(α)$ electroweak corrections a…
In this work, we investigate the production of $X_b$ in the process $Υ(5S,6S)\to γX_b$, where $X_b$ is assumed to be the counterpart of $X(3872)$ in the bottomonium sector as a $B {\bar B}^*$ molecular state. We use the effective Lagrangian based on the heavy quark symmetry to explore the rescattering mechanism and calculate their production ratios. Our results have shown that the production ratios for the $Υ(5S,6S) \to γX_b$ are orders of $10^{-5}$ with reasonable cutoff parameter range $α\simeq 2\sim 3$. The sizeable production ratios may be accessible at the future experiments like forthcom…
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