14197025
More on Violation of Angular-Momentum Selection Rules in Quantum Gravity
In a recent paper, we noticed that, in the s-channel scattering mediated by a graviton in the linearized Einstein theory, angular momentum seems not to be conserved in the graviton coupling to massive matter fields, due to the presence of a scalar component in the partial-wave expansion of the relevant amplitudes. The present Letter answers to some criticism by Han and Willenbrock, claiming that there is no problem in propagating a scalar component through a graviton exchange. We show explicitly that the partial-wave decomposition of the scattering amplitude contrasts with the rotation-group representations propagating through the graviton exchange in the considered processes. This phenomenon is crucially connected to the critical dependence of the trace of the graviton propagator on the effective dimension of the problem. In a recent work [1], we showed that angular-momentum selection rules are violated in the linearized limit of quantum gravity in the Einstein theory. In particular, we considered the scattering amplitudes of either massive fermion or massive gauge-boson pairs mediated by a graviton in the s-channel, and computed their non vanishing interferences with the amplitudes where a scalar field replaces the graviton. Since in the s-channel scattering of real particles only graviton components of angular momentum J = 2 propagate [2], a non vanishing interference with the scalar (J = 0) exchange 1 amplitude seems to point to a violation of the angular-momentum conservation in the graviton-matter vertex. Our statement was not based on special assumptions. It was derived in a straightforward way from the Feynman rules of the Einstein theory minimally coupled to massive fermion and vector-boson fields. In a following paper by Han and Willenbrock [3], it has been argued that our conclusion would be incorrect, since it is based on the wrong assumption that no J = 0 component is exchanged in the graviton propagator. The authors stress that in the s-channel amplitude mediated by a graviton, also an SO(3, 1) scalar component can propagate. The latter couples to the trace of the energy momentum tensor of the matter fields Tμν (that is non vanishing for massive fields). They conclude that there is no violation of angular-momentum selection rules in quantum gravity. In our paper [1], the crucial statement that only J = 2 graviton components contribute to the considered amplitudes was based on a previous work by van Dam and Veltman [2], and was not proved explicitly. The purpose of the present Letter is to clarify this issue, by showing that there are processes where there is a J = 0 component in the partial-wave decomposition of the s-channel amplitude, and, on the other hand, no J = 0 component propagates in the virtual graviton state. This fact will be shown to be crucially connected to the critical dependence of the trace of the graviton propagator tensor on the effective dimension of the analyzed problem. Let us consider the general form of the graviton propagator in the linearized Einstein theory. When contracted with conserved energy momentum tensors (i.e., for qμTμν = 0, with qμ the momentum flowing in the propagator), terms proportional to the momentum are not relevant, and the effective massless graviton propagator becomes∗ Gμναβ(q) = i Pμναβ q2 + iǫ ; Pμναβ = 1 2 (ημαηνβ + ημβηνα − ημνηαβ) , (1) The s-channel p1p1 → p2p2 scattering amplitude mediated by a graviton is then given by A = −i M P ( T f† μν Gμναβ(q) T i αβ ) (2) where T i(f) μν are the matrix elements of the conserved energy momentum tensor of the initial (final) states, and MP is the Planck mass. In this Letter, indices (μ, ν, α, β) are contracted according to the Minkowski metric ημν = Diag(1,−1,−1,−1).
11138073
Large extra dimension effects in Higgs boson production at linear colliders and Higgs factories
In the framework of quantum gravity propagating in large extra dimensions, the effects of virtual Kaluza-Klein graviton and graviscalar interference with Higgs boson production amplitudes are computed at linear colliders and Higgs factories. The interference of the almost-continuous spectrum of the KK gravitons with the standard model resonant amplitude is finite and predictable in terms of the fundamental D-dimensional Plank scale MD and the number of extra dimensions δ. We find that, for MD 1 TeV and δ = 2, effects of the order of a few percent could be detected for heavy Higgs bosons (mH>500 GeV) in Higgs production both via WW fusion in e+e− colliders and at μ+μ− Higgs-boson factories.
16309440
Slepton production from gauge boson fusion
We emphasize that charged slepton pairs produced via vector-boson fusion along with two high-mass, high-pT forward and backward jets (in two opposite hemispheres) can have a higher production cross section for heavy slepton masses than that from conventional Drell-Yan production at a hadronic collider such as the CERN LHC. We analyze the signal and leading backgrounds in detail in the minimal supersymmetric standard model with conserved baryon and lepton numbers. Our investigation reveals that the mass reach of the vector-boson fusion channel is certainly an improvement over the scope of the Drell-Yan mode.
118278744
Higgs Boson Signals in Three b-jet Final States at the Fermilab Tevatron
At the Fermilab Tevatron, final states with three tagged b-jets could play an important role in searches for a Higgs boson with mass in the range 100-300 GeV. These signals arise from gb fusion and we demonstrate their observability in the limit of a large b-quark Yukawa coupling. Rather promising discovery limits on such a coupling are obtained and consequent effects on the parameter space of the Higgs-boson sector in the MSSM are discussed.
12332850
New Higgs signals from vector boson fusion in R-parity violating supersymmetry
We investigate signals of the lightest neutral Higgs in an R-parity violating supersymmetric model through the vector boson fusion mechanism. Assuming that R-parity is violated through lepton number, and locating regions in the parameter space where decays of such a neutral scalar into a pair of lightest neutralinos can be significant, we proceed to calculate the event rates for final states arising from decays of the neutralinos through both $\lambda$-and $\lambda'$-type interactions. Regions of the parameter space where each of these types of interactions can lead to detectable events are identified. The possibilities where such signals can be faked by other superparticles (squarks, gluinos, charginos and neutralinos) are also investigated. It is found that over a sizable region, one can obtain distinguishable signals of an intermediate mass neutral scalar from a study of the suggested final states at the Large Hadron Collider.
118117079
Mutual consistency of the MINOS and MiniBooNE Antineutrino Results and Possible CPT Violation
Discussing the recent MINOS data on muon anti-neutrino disappearance and the MiniBooNE data on muon anti-neutrino to electron anti-neutrino oscillation, we show that the while the respective best fits are inconsistent with each other, significant overlap of allowed regions does exist. Assuming only three neutrino species, the data indicates a discrepancy of mass levels and mixing angles between the neutrino and the antineutrino sectors. We show that the existing data can be reconciled with a model of explicit CPT violation in the neutrino sector and estimate the magnitude of the required violation.
17434465
HADRONIC B DECAYS: A GENERAL APPROACH
In this paper, we propose a general approach for describing hadronic B decays. Using this method, all amplitudes for such decays can be expressed in terms of contractions, though the matrix elements are not evaluated. Many years ago, Buras and Silvestrini proposed a similar approach. However, our technique goes beyond theirs in several ways. First, we include recent theoretical and experimental developments which indicate which contractions are negligible, and which are expected to be smaller than others. Second, we show that all B-decay diagrams can be simply expressed in terms of contractions. This constitutes a formal proof that the diagrammatic method is rigorous. Third, we show that one reproduces the relations between tree and electroweak-penguin diagrams described by Neubert and Rosner, and by Gronau, Pirjol and Yan. Fourth, although the previous results hold to all orders in αs, we show that it is also possible to work order-by-order in this approach. In this way it is possible to make a connection with the matrix-element evaluation methods of QCD factorization (QCDfac) and perturbative QCD (pQCD). Finally, using the contractions approach, we reevaluate the question of whether there is a "B → πK puzzle." At , we find that the diagram ratio |C′/T′| is about 0.17, a factor of 10 too small to explain all the B → πK data. Both QCDfac and pQCD find that, at , the value of |C′/T′| may be raised to only about 2–3 times its lowest-order value. We therefore conclude that, assuming the effect is not a statistical fluctuation, it is likely that the value of |C′/T′| is similar to its result, and that there really is a B → πK puzzle.
118636509
Predictions for $B \to \tau \bar{\mu} + \mu \bar{\tau} $
The observation of $B \to \tau \bar{\mu} + \mu \bar{\tau} $ at present experiments would be a clear sign of new physics. In this paper we calculate this process in a 2HDM framework where the decay is mediated by the exchange of spin zero particle with flavour changing neutral current couplings. If we identify the scalar with the the newly discovered state at LHC with a mass $% \sim 125 $ GeV then we get $BR(B_s \to \tau \bar{\mu} + \mu \bar{\tau}) \sim 10^{-6}$ and $BR(B_d \to \tau \bar{\mu} + \mu \bar{\tau}) \sim 10^{-7}$. We also calculate this process in minimal supersymmetric standard model and find $BR(B_s \to \tau \bar{\mu} + \mu \bar{\tau}) \sim 10^{-11}$.
118664901
Nonstandard interactions of tau neutrino via charged Higgs and $W'$ contribution
We consider charged Higgs and $W'$ gauge boson contributions to the quasielastic scattering $\nu_{\tau}+ n \rightarrow \tau^- + p$ and $\bar{\nu}_{\tau}+ p \rightarrow \tau^+ + n$ . These effects modify the standard model cross section for these processes and thus impact the extraction of the neutrino mixing angles $\theta_{23}$ and $\theta_{13}$ . We include form factor effects in our calculations and find the deviation of the actual mixing angle from the measured one, assuming the standard model cross section, can be significant and can depend on the energy of the neutrino.
119214554
A 233 km tunnel for lepton and hadron colliders
A decade ago, a cost analysis was conducted to bore a 233 km circumference Very Large Hadron Collider (VLHC) tunnel passing through Fermilab. Here we outline implementations of e+e−, pp, and μ+μ− collider rings in this tunnel using recent technological innovations. The 240 and 500 GeV e+e− colliders employ Crab Waist Crossings, ultra low emittance damped bunches, short vertical IP focal lengths, superconducting RF, and low coercivity, grain oriented silicon steel/concrete dipoles. Some details are also provided for a high luminosity 240 GeV e+e− collider and 1.75 TeV muon accelerator in a Fermilab site filler tunnel. The 40 TeV pp collider uses the high intensity Fermilab p source, exploits high cross sections for pp production of high mass states, and uses 2 Tesla ultra low carbon steel/YBCO superconducting magnets run with liquid neon. The 35 TeV muon ring ramps the 2 Tesla superconducting magnets at 9 Hz every 0.4 seconds, uses 250 GV of superconducting RF to accelerate muons from 1.75 to 17.5 TeV in 6...
117242003
Azimuthal $B \to D^{*} \tau^{-} \bar{\nu_\tau}$ angular distribution with tensor operators
In a recent paper we performed a comprehensive study of the impact of new-physics operators with different Lorentz structures on $\BDstarellnu$ decays, $\ell = e^-, \mu^-, \tau^- $, involving the $b \to c l \nu_\ell$ transition. In this work we extend the previous calculation by including tensor operators. In the case of $\BDstartaunu $, we present the full three angle and $q^2$ angular distribution with tensor new physics operators with complex couplings. The impact of the tensor operators on various observables in the angular distribution, specially the azimuthal observables including the CP violating triple product asymmetries are discussed. It is shown that these azimuthal observables are very useful in discriminating different new physics operators. Finally we consider new physics leptoquark models with tensor interactions and show how the presence of additional scalar operators modify the predictions of the tensor operators.