共查询到20条相似文献,搜索用时 31 毫秒
1.
G.J. Gounaris J. Layssac P.I. Porfyriadis F.M. Renard 《The European Physical Journal C - Particles and Fields》1999,10(3):499-513
We study the helicity amplitudes and the observables of the process at high energy. As in the case of the process studied before, the relevant diagrams in the standard model (SM) involve W, charged-quark, and lepton loops, while in SUSY we also have contributions from charginos and charged-sfermion or Higgs-loop
diagrams. Above 250 GeV, the dominant SM amplitudes are themselves dominated by the W loop, and as for , they are helicity conserving and almost purely imaginary. We discuss the complementary information provided by for the identification of possible nonstandard effects. This process, together with , should provide very useful information on the nature of possible new physics particles, above the threshold of their direct
production.
Received: 26 April 1999 / Published online: 8 September 1999 相似文献
2.
G.J. Gounaris J. Layssac P.I. Porfyriadis F.M. Renard 《The European Physical Journal C - Particles and Fields》2000,13(1):79-97
We study the helicity amplitudes of the process in the Standard Model at high energy. These amplitudes receive contributions from the W and charged quark and lepton loops, analogous to those encountered in the cases studied before. But also receives contributions from the Higgs s-channel poles involving the effective Higgs- vertex. At energies , the amplitudes in all three processes are mainly helicity-conserving and almost purely imaginary; which renders them a very
useful tool in searching for New Physics. As an example, a SUSY case is studied, and the signatures due to the virtual effects
induced by a chargino-, charged slepton- or a lightest stop-loop in , are explored. These signatures, combined with the analogous ones in and , should help identifying the nature of possible New Physics particles.
Received: 3 September 1999 / Published online: 3 February 2000 相似文献
3.
We give explicit expressions for the amplitudes associated with the supersymmetric (SUSY) contributions to the process in the context of SUSY extensions of the standard model (SM) with non-universal soft SUSY breaking terms. From experimental
data we deduce limits on the squark mass insertions obtained from different contributions (gluinos, neutralinos and charginos).
Received: 20 April 2001 / Revised version: 14 December 2001 / Published online: 5 April 2002 相似文献
4.
G.J. Gounaris P.I. Porfyriadis F.M. Renard 《The European Physical Journal C - Particles and Fields》2001,19(1):57-76
If the standard model (SM) Higgs particle is sufficiently heavy, then its contribution to should be largely imaginary, interfering with the also predominantly imaginary SM “background” generated by the W loop. For standard model Higgs masses in the region GeV, this interference is found to be constructive and increasing the Higgs signal. In the minimal SUSY case an interference
effect should also appear for the contribution of the heavier CP-even neutral Higgs boson , provided it is sufficiently heavy. The effect is somewhat reduced, though, by the smallness of the width and the and ZZ branching ratios. The interference is again found to be constructive for part of the parameter space corresponding to sfermion
masses at the TeV scale and maximal stop mixing. For both the SM and the SUSY case, regions of the parameter space exist,
though, where the interference may be destructive. It is therefore essential to take these effects into account when searching
for possible scalar Higgs-like candidates. To this aim, we present the complete analytic expressions for both resonance and
background amplitudes.
Received: 20 October 2000 / Revised version: 5 January 2001 / Published online: 23 February 2001 相似文献
5.
J. Fujimoto T. Ishikawa M. Jimbo T. Kaneko T. Kon Y. Kurihara M. Kuroda Y. Shimizu Y. Yasui 《Pramana》2007,69(5):943-946
We report the recent development on the SUSY calculations with the help of GRACE system. GRACE/SUSY/1LOOP is the computer
code which can generate Feynman diagrams in the MSSM automatically and compute one-loop amplitudes in the numerical way. We
present new results of various two-body decay widths and chargino pair production at ILC (international linear collider) at
one-loop level.
相似文献
6.
Xiao-Gang He Jusak Tandean G. Valencia 《The European Physical Journal C - Particles and Fields》2009,64(4):681-687
We evaluate one-loop diagrams in the unitary gauge that contribute to flavor-changing neutral current (FCNC) transitions involving
two and four fermions. Specifically, we deal with penguin and box diagrams arising within the standard model (SM) and in nonrenormalizable
extensions thereof with anomalous couplings of the W boson to quarks. We show explicitly in the SM the subtle cancellation among divergences from individual unitary-gauge contributions
to some of the physical FCNC amplitudes and derive expressions consistent with those obtained using R
ξ gauges in the literature. Some of our results can be used more generally in certain models involving fermions and gauge bosons
which have interactions similar in form to those we consider. 相似文献
7.
S. Fajfer P. Singer J. Zupan 《The European Physical Journal C - Particles and Fields》2003,27(2):201-218
We present a calculation of the rare decay modes and in the framework of the standard model. For the short distance part we have derived QCD corrections to the Wilson coefficients
involved, including C9. The latter is found to be strongly suppressed by the corrections, leading to diminished values for the branching ratios in the 10-10 range. Within SM the exclusive decays are dominated by long distance effects. Non-resonant contributions are estimated using
heavy quark and chiral symmetries to be at the level of , compared to the contributions arising from , with . The total SM branching ratio is predicted to be in the range (1-. We also consider contributions coming from MSSM with and without R parity conservation. The effects from MSSM are significant only for the R parity violating case. Such contributions enhance the branching ratio to , based on appropriately allowed values for C9 and C10. This selects as a possible probe of new physics.
Received: 25 October 2002 / Published online: 24 January 2003 相似文献
8.
Eri Asakawa Jun-ichi Kamoshita Akio Sugamoto Isamu Watanabe 《The European Physical Journal C - Particles and Fields》2000,14(2):335-345
We present the effects of heavy CP-even (H) and CP-odd (A) Higgs bosons on the production cross section of the process
at the energy around the mass poles of the Higgs bosons. It is found that interference between H and A with small mass gap, as well as the ones between Higgs bosons and continuum, contributes to the cross section, if the photon
beams are polarized and if we observe the helicity of the top quarks. It is demonstrated in the framework of the minimal supersymmetric
extension of the standard model that the H and A contributions can be sizable at future colliders for small values of . The methods to measure the CP-parity of the Higgs boson are also presented. The statistical significance of detecting the Higgs signals and measuring the
Higgs CP-parity is evaluated.
Received: 16 December 1999 / Revised version: 30 January 2000 / Published online: 6 April 2000 相似文献
9.
Including contributions of scale-dependent vacuum expectation values, we derive new analytic formulas and obtain substantially
different numerical predictions for the running masses of quarks and charged leptons at higher scales in the SM, 2HDM and
MSSM. These formulas exhibit significantly different behaviours with respect to their dependence on gauge and Yukawa couplings
from those derived earlier. At one-loop level, the masses of the first two generations are found to be independent of the
Yukawa couplings of the third generation in all three effective theories in the small mixing limit. Analytic formulas are
also obtained for the running of in 2HDM and MSSM. Other numerical analyses include a study of the third generation masses at high scales as functions of
the low-energy values of and the SUSY scale GeV.
Received: 1 October 2000 / Revised version: 11 January 2001 / Published online: 12 April 2001 相似文献
10.
G.J. Gounaris P.I. Porfyriadis F.M. Renard 《The European Physical Journal C - Particles and Fields》2001,20(4):659-675
The process first arises at the one loop level, and as such it provides us with remarkable tests of the structure of the electroweak
Higgs sector. These tests are complementary to those in the gauge sector involving . We show that in the standard model (SM) where , as well as in the supersymmetric case where or , observables exist (like e.g. the energy dependence, angular distribution, photon polarization dependence or final Z polarization) which present rather spectacular properties. Such properties involve strong threshold effects with steps, bumps
or peaks, reflecting the type of Higgs and heavy quarks and chargino masses and couplings predicted by the SM and supersymmetric
models.
Received: 13 March 2001 / Published online: 13 June 2001 相似文献
11.
We present a complete one-loop study of the process
and the predicted cross section in a
Linear Collider. A suitable numerical code, PLATONlc, valid for any set of real MSSM parameters, is released. This study and code are complementary to those suitable for dark matter detection through the inverse process
describing neutralino-neutralino annihilation at rest, which were presented previously. If SUSY is realized in nature, both codes should be very helpful in future astrophysical and collider studies of the neutralino sector.Received: 6 November 2003, Published online: 9 January 2004Programme dActions Intégrées Franco-Hellenique, Platon 04100 UM. 相似文献
12.
Federico Buccioni Stefano Pozzorini Max Zoller 《The European Physical Journal C - Particles and Fields》2018,78(1):70
Building on the open-loop algorithm we introduce a new method for the automated construction of one-loop amplitudes and their reduction to scalar integrals. The key idea is that the factorisation of one-loop integrands in a product of loop segments makes it possible to perform various operations on-the-fly while constructing the integrand. Reducing the integrand on-the-fly, after each segment multiplication, the construction of loop diagrams and their reduction are unified in a single numerical recursion. In this way we entirely avoid objects with high tensor rank, thereby reducing the complexity of the calculations in a drastic way. Thanks to the on-the-fly approach, which is applied also to helicity summation and for the merging of different diagrams, the speed of the original open-loop algorithm can be further augmented in a very significant way. Moreover, addressing spurious singularities of the employed reduction identities by means of simple expansions in rank-two Gram determinants, we achieve a remarkably high level of numerical stability. These features of the new algorithm, which will be made publicly available in a forthcoming release of the OpenLoops program, are particularly attractive for NLO multi-leg and NNLO real–virtual calculations. 相似文献
13.
We describe a general method that enables us to obtain all the singular terms of helicity amplitudes of n-parton processes at one loop. The algorithm uses helicity amplitudes at tree level and simple color algebra. We illustrate the method by calculating the singular part of the one-loop helicity amplitudes of all 2 → 3 parton subprocesses. The results are used to derive the soft gluon limit of the cross sections of all 2 → 4 parton scattering subprocesses which provide a useful initial condition for the angular ordering approximation to coherent multiple soft gluon emission, incorporated in existing Monte Carlo simulation programs. 相似文献
14.
J. Bernabéu F.J. Botella O. Vives 《The European Physical Journal C - Particles and Fields》1999,7(2):205-215
We study the -Z interference in the process as a means to measure the neutral current coupling of the b-quark. The helicity amplitudes are calculated from resonant and
background diagrams and the spin density matrix of the final state is discussed. The spin analyzer of the 's is illustrated with the decays and . With a sensitivity to of a few per cent could be reachable.
Received: 14 April 1998 / Revised version: 25 August 1998 / Published online: 3 December 1998 相似文献
15.
The mass spectrum of the chargino–neutralino sector in the minimal supersymmetric standard model (MSSM) is calculated at
the one-loop level, based on the complete set of one-loop diagrams. On-shell renormalization conditions are applied to determine
the counterterms for the gaugino-mass-parameters and the Higgsino-mass parameter . The input is fixed in terms of three pole masses (two charginos and one neutralino); the other pole masses receive a shift
with respect to the tree-level masses, which can amount to several GeV. The detailed evaluation shows that both the fermionic/sfermionic
loop contributions and the non-(s)fermionic loop contributions are of the same order of magnitude and are thus relevant for
precision studies at future colliders.
Received: 26 April 2002 / Published online: 21 June 2002 相似文献
16.
The dependence of the K + → π 0 l + ν lγ decay rate on the T-odd kinematical variable ξ = q · [p l × p π]/m K 3 is investigated in the tree and one-loop approximations of the Standard Model (SM). It is shown that the partial width of the decay on the tree level is an even function of the variable ξ, whereas the odd component is generated by the electromagnetic final-state interaction and determined by the imaginary parts of one-loop diagrams. The ξ-odd components of the partial widths of the K + → π 0e+ ν e γ and K + → μ 0μ+ ν μ γ decays calculated in the one-loop approximation are smaller by four orders of magnitude than the even components evaluated from the tree-level SM diagrams. 相似文献
17.
A. Dobado M.J. Herrero S. Peñaranda 《The European Physical Journal C - Particles and Fields》2000,12(4):673-700
In the framework of the minimal supersymmetric standard model we compute the one-loop effective action for the electroweak
bosons obtained after integrating out the different sleptons, squarks, neutralinos and charginos, and present the result in
terms of the physical sparticle masses. In addition we study the asymptotic behavior of the two-, three- and four-point Green's
functions with external electroweak bosons in the limit where the physical sparticle masses are very large in comparison with
the electroweak scale. We find that in this limit all the effects produced by the supersymmetric particles can either be absorbed
in the standard model parameters and gauge bosons wave functions, or else they are suppressed by inverse powers of the supersymmetric
particle masses. This work, therefore, completes the proof of decoupling of the heavy supersymmetric particles from the standard
ones in the electroweak bosons effective action and in the sense of the Appelquist–Carazzone theorem; we started this proof
in a previous work. From the point of view of effective field theories this work can be seen as a (partial) proof that the
SM can indeed be obtained from the MSSM as the quantum low-energy effective theory of the latter when the SUSY spectra are
much heavier than the electroweak scale.
Received: 27 March 1999 / Revised version: 7 September 1999 / Published online: 27 January 2000 相似文献
18.
C.A. Nelson 《The European Physical Journal C - Particles and Fields》2001,19(2):323-337
Due to the absence of hadronization effects and the large mass, top quark decay will be uniquely sensitive to fundamental electroweak physics at the Tevatron, at the LHC, and at a
future linear collider. A “complete measurement” of the four helicity amplitudes in decay is possible by the combined use of andW polarimetry in stage-two spin-correlation functions (S2SC). In this paper, the most general Lorentz-invariant decay density
matrix is obtained for the decay sequence where and [or ], and likewise for . These density matrices are expressed in terms of b-polarimetry helicity parameters which enable a unique determination of the relative phases among the amplitudes. Thereby, S2SC distributions and single-sided b-W-interference distributions are expressed in terms of these parameters. The four b-polarimetry helicity parameters involving the amplitude are considered in detail. polarimetry signatures will not be suppressed in top quark analyses when final angles-and-energy variables are used for .
Received: 26 January 2001 / Published online: 15 March 2001 相似文献
19.
On non-commutative spacetime, the standard model (SM) allows new, usually SM forbidden, triple gauge boson interactions to
occur. In this letter we propose the SM strictly forbidden
and
decay modes coming from the gauge sector of the non-commutative standard model (NCSM) as a place where non-commutativity
could be experimentally discovered.
Received: 2 July 2002, Revised: 28 February 2003, Published online: 18 June 2003 相似文献
20.
P.G. Ratcliffe 《The European Physical Journal C - Particles and Fields》1999,8(3):403-408
We analyse the twist-three amplitudes that can give rise to single-spin asymmetries in hadron-hadron scattering; in so doing
we bring to light a novel factorisation property. As already known, the requirement of an imaginary part leads to consideration
of twist-three contributions that are also related to transverse spin in deep-inelastic scattering. In particular, when an
external line becomes soft in contributions arising from three-parton correlators, the imaginary part of an internal propagator
may be exposed. As shown here, it is precisely this kinematical configuration that permits the factorisation. An important
feature is the resulting simplification: the calculation of tens of Feynman diagrams normally contributing to such processes
is reduced to the evaluation of products of the simple factors derived here and known two-body helicity amplitudes. We thus
find clarifying relations between the spin-dependent and spin-averaged cross-sections and formulate a series of selection
rules. In addition, the kinematical dependence of such asymmetries, is rendered more transparent.
Received: 31 July 1998 / Revised version: 12 November 1998 / Published online: 11 March 1999 相似文献