31402321
Renormalization of $NN$ scattering: contact potential
The renormalization of the T -matrix for NN scattering with a contact potential is reexamined in a nonperturbative regime through rigorous nonperturbative solutions. Based on the underlying theory, it is shown that the ultraviolet divergences in the nonperturbative solutions of the T -matrix should be subtracted through ”endogenous” counter terms, which in turn leads to a nontrivial prescription dependence. Moreover, employing the effective range expansion, the importance of imposing physical boundary conditions to remove the nontrivial prescription dependence, especially before making physical claims, is discussed and highlighted. As byproducts, some relations between the effective range expansion parameters are derived. We also discuss the power counting of the couplings for the nucleon-nucleon interactions and other subtle points present within EFT framework beyond perturbative treatment.
13049479
A new kind of constraints on renormalization schemes
We derive a new kind of physical constraints on the subtraction schemes for theories with massive particles in addition to the Ward identities for gauge symmetries. The momentum subtraction scheme fails this criterion. The decoupling of heavy fields is discussed in the context of Callan-Symanzik equations where all schemes (including MOM) lead to the same pattern of decoupling with inevitable discontinuities in beta function across heavy field thresholds. PACS number(s): 11.10.Gh; 11.10.Hi; 12.39.Hg
15356070
Can QFT be UV finite as well as effective
A new attempt is demonstrated that QFTs can be UV finite if they are viewed as the low energy effective theories of a fundamental underlying theory (complete and well-defined in all respects) according to the modern standard point of view. This approach is much simpler in principle and in technology comparing to any known renormalization program. Some subtle and difficult issues can be easily resolved. The importance of the procedure for defining the ambiguities is fully appreciated in the new approach. Some simple but important nonperturbative examples are discussed to show the power and plausibility of the new approach.
120520076
Soliton mass and discrete coupling constants in the quantized sine-Gordon model
The soliton mass in the quantized sine-Gordon model over the whole range of the coupling constant (g2 from 0 to 8 pi ) is evaluated by means of the Gaussian effective potential method. The analytical expression with numerical results is presented. The authors find that the coupling constant g can only take discrete values. A new kind of soliton linking g Phi =0 to g Phi = pi emerges at a set of special coupling constants g.
14239579
Confinement of Higgs bosons from hidden symmetry and convexity
In the full effective potential (EFP) approach, we find that spontaneous symmetry breaking (SSB) can, with the convexity of the full EFP, lead to the prediction of the IR confinement of Higgs particles, adding difficulty to the experimental identification of Higgs particles. The short distance behaviors remain intact. The whole presentation is given in the understanding that any QFT becomes UV well defined in a more complete underyling theory according to a recently proposed strategy.
119670186
Padé Expansion and the Renormalization of Nucleon–Nucleon Scattering
The importance of imposing physical boundary conditions on the T-matrix to remove the nonperturbative renormalization prescription dependence is stressed and demonstrated in two diagonal channels 1P1 and 1D2, with the help of Pade expansion.
204212123
The Spectrum of a Binding System for a Heavy Quark with an Anti-Sbottom or for a Sbottom and Anti-Sbottom Pair
Since long-lived light bottom squark (sbottom) and its anti-particle with a mass close to the bottom quark have not been excluded by experiments so far, we consider such a sbottom to combine with its anti-particle to form a color singlet meson-like bound state or to combine with a common anti-quark to form a fermion-like one, or accordingly their anti-particles to form an anti-particle bound system. Namely we calculate the low-lying spectrum of the systems based on QCD inspired potential model. To be as relativistic as possible, we start with the framework of Bethe-Salpeter (BS) equation even for non-relativistic binding systems. Finally, we obtain the requested spectrum by constructing general forms of the BS wave functions and solving the BS equations under instantaneous approximation.
123742445
The Deconfinement Transition in SU(2) Lattice Gauge Theory: An Analytical Study
We study SU(2) lattice gauge theory at finite temperature in the variational cumulant expansion approach. The deconfinement transition is given in four and five dimensions. The comparison with Monte Carlo results is also presented.
18486610
Top anomalous decays in R-parity violating SUSY
The flavor-changing top-quark decay t → ch, where h is the lightest CPeven Higgs boson in the minimal supersymmetric standard model, is examined in the R-parity-violating supersymmetric model. Within the existing bounds on the relevant R-parity-violating couplings, the branching ratio for t→ ch can be as large as about 10−5 in some part of the parameter space, reaching a level accessible at the LHC and at e+e− Linear Colliders with high luminosities. The study of heavy-particle decays via flavor-changing neutral-currents (FCNC) has been playing an important role in testing the standard model (SM) and probing new physics beyond the SM. As the heaviest elementary particle in the SM with a mass at the electroweak scale, the top quark is more likely to be sensitive to new physics. Kinematically it is accessible to many FCNC decay modes, such as t → cV (V = γ,Z, g) and t → ch, where h is a Higgs boson. In the SM these FCNC decay modes are highly suppressed by the GIM mechanism, with typical branching ratios of 10−14 − 10−10 [1, 2], which are too small to be detectable at collider experiments. On the other hand, observation of any of such FCNC top-quark decays would be robust evidence for new physics [3, 4, 5, 6]. Top quarks will be copiously produced at the next generation of colliders. At Tevatron II with an integrated luminosity of 10 fb−1, there will be about 8×104 top quarks produced, ∗Speaker. P r H E P h e p 2 0 0 1 International Europhysics Conference on HEP G. Eilam while there will be about 100 times more at the LHC with the same luminosity. At the LHC with a luminosity of 100 fb−1 there will be more than 108 tops per year, including both tt̄ and single top production, for mh = 120 GeV [7]. At a proposed e +e− Linear Collider with √ s = 500 GeV and luminosity of 300 fb−1, such as TESLA, one expect 1.6× 105 tops [7, 8]. With such large data samples, good sensitivities may be reached for the rare decay channels t → cV [3], and for studying other related processes at hadron colliders [4]. A more recent study showed that the channel t→ ch could also be detectable [5], reaching a sensitivity of Br(t → ch) ∼ 10−5 at the LHC and a few percent at the Tevatron. While these high detection sensitivities are still far above the SM expectation for the rare decay channels [1, 2], in many scenarios beyond the SM the branching ratios of these FCNC top-quark decays could be significantly enhanced [1, 6, 9, 10, 11, 12, 13]. In the minimal supersymmetric (SUSY) standard model (MSSM) with R-parity conservation, it was shown [10] that the possibility for observing the decay channel t → ch could be greatly enhanced (here h is the lightest CP-even Higgs boson). Kinematically this decay mode is always allowed because of the strict theoretical upper bound on the Higgs boson mass [14], and the decay receives dominant contributions from the SUSY QCD (SQCD) loops of flavor-changing interactions [10]. If the gluino and squarks involved in the contributing SQCD loops are both light of order 100 GeV, the branching ratio could be enhanced to a level of 10−5. The branching ratio falls off quickly for heavier sparticles in the loops. In this talk which is basically a short version of [15], we examine the R-parity-violating contributions to t→ ch. It is well-known that R-parity conservation in SUSY theory, which implies the separate conservation of baryon number and lepton number, is put in by hand. R-parity violation ( 6 R) can be made perfectly consistent with other fundamental principles such as gauge invariance, supersymmetry and renormalizability [16]. If 6 R is included in the MSSM, t→ ch will receive new contributions from the loops of 6 R interactions. These can be significant, since the relevant 6 R couplings inducing t→ ch involve the third-generation fermions and are subject to rather weak bounds from existing experiments. We find that the branching ratio for t→ ch from 6 R contributions can be indeed as high as about 10−5 in some part of parameter space, reaching a level accessible at future high luminosity colliders. Assuming that there are only trilinear couplings, one obtains the 6 R Lagrangian Lλ′′ = − 2 λ′′ ijk [ d̃R(ū i R) d j R + d̃ j R(d̄ k R) uR + ũ i R(d̄ j R) dR ] + h.c. (1) Constraints on the couplings have been obtained from various processes [17, 18, 19, 20, 21, 22, 23, 24] and their phenomenology at hadron and lepton colliders has been intensively investigated [24, 25]. For brevity, only the terms with Baryon-number violation ( 6B) are displayed, and the similar Lepton-number violating (6L) terms, i.e. those with λ′’s, are left out. Also, the limits on the 6 L couplings are stricter than for those with 6 B. With 6 B couplings, the decay t → ch can proceed through four simple 1-loop diagrams (see Fig. 1 in [15]). The induced effective tch vertex is given by V = ie λ′′ 2jkλ ′′ 3jk 16π2 2FPL, where PL = 1 2 (1 − γ5). For simplicity and space limitation, we have assumed that all fermion masses can
14034966
Probing anomalous top quark interactions at the Fermilab Tevatron collider
We study the effects of dimension-six operators contributing to the $\mathrm{gt}\overline{t}$ vertex in top quark pair production at the Fermilab Tevatron collider. We derive both the limits from run 1 data and the potential bounds from future runs (runs 2 and 3). Although the current constraints are not very strong, the future runs are quite effective in probing these operators. We investigate the possibility of disentangling different operators with the $t\overline{t}$ invariant mass distribution and the top quark polarization asymmetry. We also study the effects of a different set of operators contributing to single top quark production via the $\mathrm{Wt}\overline{b}$ coupling. We derive the current and potential future bounds on these anomalous operators and find that the upgraded Fermilab Tevatron collider can improve the existing constraints from ${R}_{b}$ for one of the operators.
15804712
Probing R-violating top quark decays at the NLC
Abstract We examine the possibility of observing exotic top quark decays via R -parity violating SUSY interactions in e + e − collisions at s =500  GeV. We present cross-sections for t t production followed by the subsequent decay of either the t or t via the R -parity violating interaction while the other undergoes the SM decay. We discuss kinematic cuts that allow the exotic SUSY decays to be detected over standard model backgrounds. Discovery limits for R -parity violating couplings in the top sector are presented assuming an integrated luminosity of 100 fb −1 .