7709022
Finiteness following from underlying theory: a natural strategy
A tentative proposal is demonstrated that there is a natural strategy to get rid of unphysical (UV) infinities in QFTs if one adopts the modern standard point of view that a fundamental theory that is complete and well-defined in all respects underlies the QFTs. This simple strategy works in principle for any interaction model and space-time dimension. It provides a physical rationality behind the UV divergence and the conventional renormalization programs and improves the latter in several important aspects.
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.
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.
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
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.
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.
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
119779961
Phase structure of Abelian Higgs model on a lattice: an analytical analysis
The variational cumulant expansion is extended to d-dimensional U(1) gauge theory with radially active Higgs fields in the fundamental representation. The phase structures are given for d=3 and d=4 cases. A comparison with Monte Carlo and mean field results is also presented.
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.
119090694
Probing topcolor-assisted technicolor from like-sign top pair production at CERN LHC
The topcolor-assisted technicolor (TC2) theory predicts tree-level flavor-changing neutral-current (FCNC) top quark Yukawa couplings with top-pions. Such FCNC interactions will induce like-sign top quark pair productions at CERN Large Hadron Collider (LHC). While these rare productions are far below the observable level in the Standard Model and other popular new physics models such as the Minimal Supersymmetric Model, we find that in a sound part of parameter space the TC2 model can enhance the production cross sections to several tens of fb and thus may be observable at the LHC due to rather low backgrounds. Searching for these productions at the LHC will serve as an excellent probe for the TC2 model.
118390410
Light dark matter from the U(1)(X) sector in the NMSSM with gauge mediation
Cosmic ray anomalies observed by PAMELA and Fermi-LAT experiments may be interpreted by heavy (TeV-scale) dark matter annihilation enhanced by Sommerfeld effects mediated by a very light (sub-GeV) U(1)(X) gauge boson, while the recent direct searches from CoGeNT and DAMA/LIBRA experiments may indicate a rather light (similar to 7GeV) dark matter with weak interaction. Motivated by these apparently different scales, we consider a gauge mediated next-to-the minimal supersymmetric standard model (NMSSM) entended with a light U(1)(X) sector plus a heavy sector ((H) over barh, Hh), which can provide both a light (similar to 7GeV) and a heavy (TeV-scale) dark matter without introducing any ad hoc new scale. Through the Yukawa coupling between Hh and the messager fields, the U(1)(X) gauge symmetry is broken around the GeV scale radiatively and a large negative m(S)(2) is generated for the NMSSM singlet S. Furthermore, the small kinetic mixing parameter between U(1)(X) and U(1)(Y) is predicted to be theta similar to 10(-5) - 10(-6) after integrating out the messengers. Such a light dark matter, which can have a normal relic density from the late decay of the right-handed sneutrino (assumed to be the ordinary next-to-the lightest supersymmetric particle and thermally produced in the early Universe), can serve a good candidate to explain the recent CoGeNT and DAMA/LIBRA results.