arXiv subjects

B. Holdom

Publications and source records attributed to B. Holdom.

At least 73 records · Page 4Linked to original sources

arXiv1995

A New Physics Source of Hard Gluons in Top Quark Production

We consider the contribution of new strongly interacting sector, with a characteristic scale of half a TeV, to top quark production at the Tevatron. The color-octet, isosinglet analog of the $ρ$ meson in this theory is produced copiously in hadron colliders. If the mass of this resonance is less than twice the mass of the lightest pseudo-Goldstone bosons, then an important decay mode could be to the color-octet analog of the $η$ and a gluon. The subsequent decay of this $η$ into $\ttbar$ gives rise to top quark events with a hard gluon.

hep-ph↗

arXiv1995

Momentum dependent quark mass in two-point correlators

A momentum dependent quark mass may be incorporated into a quark model in a manner consistent with dynamically broken chiral symmetry. We use this to study the high $Q^2$ behavior of the vector, axialvector, scalar and pseudoscalar two-point correlation functions. Expanding the results to order $1/Q^6$, we show the correspondence between the dynamical quark mass and the vacuum condensates which appear in the operator product expansion of QCD. We recover the correct leading logarithmic $Q^2$ dependence of the various terms in the OPE, but we also find substantial subleading corrections which are numerically huge in a specific case. We conclude by using the vector minus axialvector correlator to estimate the $π^+ - π^0$ electromagnetic mass difference.

hep-ph↗

arXiv1995

New Third-family Flavor Physics: Vertex Corrections

As described previously, a new massive gauge boson (X) coupling only to the third family produces a tantalizing pattern of deviations away from the standard model. These include increasing Gamma_b/Gamma_h and decreasing the alpha_s(M_Z) extracted from Gamma_h/Gamma_ell . We review the status of these X-Z mixing effects. We then calculate X boson induced vertex corrections to Z partial decay widths and to ttbar production in ppbar colliders.

hep-ph↗

arXiv1994

New strong sector, odd-parity processes, and the Tevatron

The color-octet isosinglet "rho" of a new strong-interaction sector is readily produced in ppbar collisions. Its odd-parity decay to an "eta" and a gluon may exceed its decay rate to dijets. At center of mass energies sufficiently greater than the colored "rho" mass, the odd-parity production of ("omega" + colored "eta") or ("rho" + colored "pion") may be comparable to ttbar production. Considering that the "omega" has a dominant odd-parity decay mode, we end up with (Z, W, or gamma) + 4 jet events with two of the jets containing b or bbar.

hep-ph↗

arXiv1994

Simply Modeling Meson HQET

A simple relativistic model of heavy-quark-light-quark mesons is proposed. In an expansion in inverse powers of the heavy quark mass we find that all zeroth and first order heavy quark symmetry relations are satisfied. The main results are: - the difference between the meson mass and the heavy quark mass plays a significant role even at zeroth order; - the slope of the Isgur-Wise function at the zero recoil point is typically less than $-1$; - the first order correction to the pseudoscalar decay constant is large and negative; - the four universal functions describing the first order corrections to the semileptonic decay form factors are small; - these latter corrections are quite insensitive to the choice of model parameters, and in particular to the effects of hyperfine mass splitting.

hep-ph↗

arXiv1994

Linear and higher order power corrections in semileptonic B decays

In previous work we have developed a relativistic quark model of mesons which is consistent with all QCD constraints at zeroth and first order in the heavy quark expansion. Here we obtain first order model predictions for the differential decay spectrum, the forward-backward asymmetry $A_{FB}$ and the $D^{\ast}$ polarization parameter $α$ in the decay $B\to D^{\ast}\ellν$. We compare these with the predictions of QCD sum rules at first order. The model suggests why the corrections allowed at first order are small, concurrently with substantial corrections at second order.

hep-ph↗

arXiv1994

What can a relativistic quark model tell us about charmed mesons?

A relativistic quark model is extended to incorporate chiral and gauge symmetries. We obtain the DD*pi and DD*gamma couplings and find that the ratio Gamma(D*0->D0pi0)/Gamma(D*0->D0gamma) constrains the charm-quark mass close to 1.45 GeV. Large 1/mc corrections appear in the heavy-quark contribution to the DD*gamma coupling. The model is extended further to describe seven excited D meson states. We find that semileptonic B decays into the ground and excited D meson states do not account for the total semileptonic decay width of the B0. The nonresonant contributions to the processes B0->D(*)pi+ell+nu appear to be large enough to account for the discrepancy.

hep-ph↗

arXiv1994

Hints of New Flavor Physics at LEP?

A massive gauge boson coupling to the third family but not lighter families mixes with the $Z$. The $Z$ partial width to $b\overline{b}$ increases, the $τ$ asymmetry parameter increases, the invisible width of the $Z$ decreases, and $α_s(m_Z)$ decreases, all in a manner consistent with present data.

hep-ph↗

arXiv1994

A Dynamical Origin for the Top Mass

We describe a dynamical scheme by which isospin breaking feeds strongly into the $t$ and $b$ masses and not into the $W$ and $Z$ masses. The third family feels a new gauge interaction broken close to a TeV.

hep-ph↗

arXiv1994

Anomalous Thresholds and the Isgur-Wise Function

The original de Rafael-Taron bound on the slope of the Isgur-Wise function at zero recoil is known to be violated in QCD by singularities appearing in an unphysical region. To be consistent, quark models must have corresponding singularity structures. In an existing relativistic quark-loop model, the meson-quark-antiquark vertex is such that the required singularity is an anomalous threshold. We also discuss the implications of another anomalous threshold, whose location is determined by quark masses alone.

hep-ph↗

arXiv1994

Hadronic contribution to the photon vacuum polarization: a theoretical estimate

A simple model for the hadronic contribution to the photon vacuum polarization function $Π_{had}(q^2)$, for spacelike momenta, is presented. For small momenta, the two loop contribution from the pseudoscalar meson octet is computed from the chiral Lagrangian. The light quark contribution (which at low momentum gives the ${\cal O}(q^6)$ counterterm in the chiral Lagrangian) is calculated within a relativistic constituent quark model incorporating the momentum dependence of the quark mass. The perturbative gluons of QCD are included in a standard fashion. The total result is close to an estimate of $Π_{had}(q^2)$ that is obtained directly from $e^+e^-\to hadrons$ data. We further use our results for $Π_{had}(q^2)$ to calculate the ${\cal O}(e^4)$ hadronic contribution to lepton magnetic moments and to calculate $α_{QED}(M_Z^2)$. A simpler model of constituent quarks with momentum independent masses gives less favourable results.

hep-ph↗

arXiv1994

Effects of technicolor on standard model running couplings

We discuss the running couplings in the standard model, SU(3$)_C \times $SU(2$)_L \times $U(1$)_Y$, when the Higgs sector is replaced by SU($N_{TC})$ technicolor. Particular attention is given to the running of the couplings at momentum scales where technicolor is nonperturbative, and in this region we apply a relativistic constituent technifermion model. This model has been tested against the known running of the QED coupling due to nonperturbative QCD. An understanding of this low momentum running allows the calculation of the couplings at a higher scale, $Λ_{pert}$, where technicolor becomes perturbative. We provide numerical values for the changes in the three standard model couplings between $m_Z$ and $Λ_{pert}$ due to technicolor, assuming separately ``one doublet'' and ``one family'' technicolor models. The distinction between a running and walking technicolor coupling is also considered.

hep-ph↗

arXiv1993

Cosmic balloons

Cosmic balloons, consisting of relativistic particles trapped inside a spherical domain wall, may be created in the early universe. We calculate the balloon mass $M$ as a function of the radius $R$ and the energy density profile, $ρ(r)$, including the effects of gravity. At the maximum balloon mass $2GM/R\approx 0.52$ for any value of the mass density of the wall.

hep-ph↗

arXiv1993

Comparison of 1/mQ^2 Corrections in Mesons and Baryons

We extend our relativistic quark model to the study of the decay Lambda_b -> Lambda_c ell nu and verify that the model satisfies the heavy-quark symmetry constraints at order 1/mQ^2. We isolate a strong dependence on a parameter which measures the relative distortion in the light-quark wave functions of the Lambda_b and Lambda_c. This parameter and the 1/mQ^2 corrections turn out to be small. The dependence on a corresponding parameter in the meson case leads to large 1/mQ^2 corrections.

hep-ph↗

arXiv1993

Simply Modeling B -> K* gamma

A simple relativistic model of heavy-light mesons is applied to the rare decay B -> K* gamma in the standard model. We find Gamma(B -> K* gamma)/Gamma(b -> s gamma)=(17 \pm 4)% and BR(B -> K* gamma)=(4.8 \pm 1.9) \times 10^{-5}(V_cb/.04)^2. These numbers are reduced by only 20% in the heavy-quark limit.

hep-ph↗

arXiv1993

Hyperfine Effects and Large $1/{m}_{Q}^{2}$ Corrections

Effects associated with hyperfine mass splitting between pseudo\-scalar and vector mesons may induce surprisingly large $1/{m}_{Q}^{2}$ corrections in the heavy quark expansion. We demonstrate this in a relativistic quark model by calculating to all orders in $1/{m}_{Q}$, with and without hyperfine effects, and comparing to the first order results. Total corrections of 30\% or more are quite possible in the decay rates for $B\rightarrow Dlν$ and $B\rightarrow D^{\ast}lν$ near zero recoil.

hep-ph↗

arXiv1993

Metacolor

A new mechanism is presented for the generation of quark and lepton masses, based on a heavy fourth family and a new sector of massless fermions. The massless fermions have only discrete chiral symmetries and they are confined by the metacolor force. The resulting electroweak corrections may be smaller than in technicolor theories.

hep-ph↗

arXiv1993

Neutrino Balls and Gamma-Ray Bursts

We propose a mechanism by which the neutrino emission from a supernova-type explosion can be converted into a gamma-ray burst of total energy $\sim 10^{50}$ ergs. This occurs naturally if the explosion is situated inside a ball of trapped neutrinos, which in turn may lie at a galactic core. There are possible unique signatures of this scenario.

astro-ph↗