45314613
Numerical evaluation of a two loop diagram in the cutoff regularization
Dimensional regularization [1] has become an efficient regularization scheme for theoretical calculations in high energy physics. It makes analytical results more available, and its gauge invariance almost decisively defeated the other schemes (say cutoff scheme) in QCD and other gauge theories. However, things are not so simple. It is very natural to anticipate that DR might fail sooner or later somewhere as it is just a special regularization but never a true theory of the short distance physics. Such event is now known: the MS scheme does not provide a physical prediction for low energy nucleons scattering in case of long scattering lengths [2] in nonperturbative context. To yield meaningful results, unconventional subtraction is devised and now known as PDS [2]. Since this is obtained with hindsight, we should not discard the cutoff scheme without further exploiting its virtues. There have recently been some further investigations over the relations between the divergences in DR and cutoff schemes and the associated limitations [4,5]. The conventional virtues of the DR scheme were shown to be due to an implicit subtraction [4]. In nonperturbative contexts involving multiloop corrections the DR might even make renormalization infeasible [5]. Traditionally, it is very hard to obtain analytical results for multiloop amplitudes within the cutoff scheme. In this report we show that one could achieve this goal numerically at a pretty good precision. We will make use of the dynamical symmetry breaking of λφ discussed in [6] to illustrate the numerical evaluation of the finite constant term in the two loop sunset diagram. Thus the report is organized as follows. First we quote some results of Ref. [6] in Sec. II as preparation. In Sec. III we present our strategy and procedures for doing the numerical analysis of the problem and its possible prospective significance. The result is also given there. In Sec. IV we revisit the problem introduced in Sec. II to show the significance of the new result obtained in Sec. III. The summary will also be given there.
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.
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.
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.
119274047
Structure function of holographic quark-gluon plasma: Sakai-Sugimoto model versus its noncritical version
Motivated by recent studies of deep inelastic scattering off the N = 4 super-Yang-Mills (SYM) plasma, holographically dual to an AdS(5) x S(5) black hole, we use the spacelike flavor current to probe the internal structure of one holographic quark-gluon plasma, which is described by the Sakai-Sugimoto model at high temperature phase (i.e., the chiral-symmetric phase). The plasma structure function is extracted from the retarded flavor current-current correlator. Our main aim in this paper is to explore the effect of nonconformality on these physical quantities. As usual, our study is under the supergravity approximation and the limit of large color number. Although the Sakai-Sugimoto model is nonconformal, which makes the calculations more involved than the well-studied N = 4 SYM case, the result seems to indicate that the nonconformality has little essential effect on the physical picture of the internal structure of holographic plasma, which is consistent with the intuition from the asymptotic freedom of QCD at high energy. While the physical picture underlying our investigation is same as the deep inelastic scattering off the N = 4 SYM plasma with(out) flavor, the plasma structure functions are quantitatively different, especially their scaling dependence on the temperature, which can be recognized as model dependent. As a comparison, we also do the same analysis for the noncritical version of the Sakai-Sugimoto model which is conformal in the sense that it has a constant dilaton vacuum. The result for this noncritical model is quite similar to the conformal N = 4 SYM plasma. We therefore attribute the above difference to the effect of nonconformality of the Sakai-Sugimoto model.
17604385
The SU(3)(C) x SU(4)(W) x U(1)B-L models with left-right unification
Abstract To understand the origin of the left–right symmetry, we study a partial unification model based on SU ( 4 ) W × U ( 1 ) B − L which can be broken down to the minimal left–right model either through the Higgs mechanism in four dimensions or through the five-dimensional orbifolding gauge symmetry breaking, especially we propose to use the rank reducing outer automorphism orbifolding breaking mechanism. We scrutinized all these breaking mechanisms and found that for the orbifold breaking in five dimensions, the rank-reducing outer automorphism is better than the inner automorphism and can make the low energy theory free of the U ( 1 ) Z anomaly. It is possible for the outer automorphism orbifolding breaking mechanism to be non-anomalous without Chern–Simons terms and new localized fermions. For the four-dimensional model with the Higgs mechanism, we study in detail both its structure and its typical phenomenology. It turns out that this four-dimensional scenario may predict some new phenomenology since the new mirror fermions (which are introduced in order to fill the SM fermions into SU ( 4 ) W without anomaly) are preserved at low energy scale and mix with the SM fermions. We also examine the gauge coupling unification in each case, and discuss the possibility for unifying this partial unification group with the Pati–Salam group SU ( 4 ) PS to realize a grand unification.
119516872
Muon anomalous magnetic moment in technicolor models
Contributions to the muon anomalous magnetic moment are evaluated in the technicolor model with scalars and topcolor assisted technicolor model, In the technicolor model with scalers, the additional contributions come from the loops of scalers, which were found sizable only for a very large f/f' disfavored by the experiment of h --> s gamma. The topcolor effect is also found to be large only for an unnaturally large tan theta', and thus the previously evaluated loop effects of extended technicolor bosons, suppressed by m(mu)(2)/M-ETC(2), must be resorted to account for the E821 experiment. So, if the E821 experiment result persists, it would be a challenge to technicolor models. (C) 2001 Published by Elsevier Science B.V.
119218719
Spectral function and quark diffusion constant in non-critical holographic QCD
Motivated by recent studies of intersecting D-brane systems in critical string theory and phenomenological AdS/QCD models, we present a detailed analysis for the vector and scalar fluctuations in a non-critical holographic QCD model in the high temperature phase, i.e., the chiral symmetric phase. This model is described by N-f pairs of D4 and (D4) over bar probe branes in a non-critical AdS(6) black hole background. Focusing on the hydrodynamic as well as the high frequency limit, we analytically obtain spectral functions for vector and scalar modes on the flavor probe. Then we extract the light quark diffusion constant for flavor current using three different methods and find that different methods give the same results. We also compute the heavy quark diffusion constant for comparison with the light quark case. (C) 2011 Elsevier B.V. All rights reserved.
118655875
Split-SUSY dark matter in light of direct detection limits
We examine the present and future XENON limits on the neutralino dark matter in split supersymmetry (split-SUSY). Through a scan over the parameter space under the current constraints from collider experiments and the WMAP measurement of the dark matter relic density, we find that in the allowed parameter space a large part has been excluded by the present XENON100 limits and a further largish part can be covered by the future exposure (6000 kg day). In case of unobservation of dark matter with such an exposure in the future, the lightest neutralino will remain bino-like and its annihilation is mainly through exchanging the SM-like Higgs boson in order to get the required relic density. (C) 2011 Elsevier B.V. All rights reserved.