arXiv subjects

Eric Braaten

Publications and source records attributed to Eric Braaten.

At least 127 records · Page 7Linked to original sources

arXiv2004

Production of the X(3872) in B Meson Decay by the Coalescence of Charm Mesons

If the recently-discovered charmonium state X(3872) is a loosely-bound S-wave molecule of the charm mesons \bar D^0 D^{*0} or \bar D^{*0} D^0, it can be produced in B meson decay by the coalescence of charm mesons. If this coalescence mechanism dominates, the ratio of the differential rate for B^+ \to \bar D^0 D^{*0} K^+ near the \bar D^0 D^{*0} threshold and the rate for B^+ \to X K^+ is a function of the \bar D^0 D^{*0} invariant mass and hadron masses only. The identification of the X(3872) as a \bar D^0 D^{*0}/\bar D^{*0} D^0 molecule can be confirmed by observing an enhancement in the \bar D^0 D^{*0} invariant mass distribution near the threshold. An estimate of the branching fraction for B^+ \to X K^+ is consistent with observations if X has quantum numbers J^{PC} = 1^{++} and if J/ψπ^+ π^- is one of its major decay modes.

hep-ph↗

arXiv2004

Enhanced Dimer Relaxation in an Atomic/Molecular BEC

We derive a universal formula for the rate constant βfor relaxation of a shallow dimer into deeply-bound diatomic molecules in the case of atoms with a large scattering length a. We show that βis determined by a and by two 3-body parameters that also determine the binding energies and widths of Efimov states. The rate constant βscales like \hbar a/m near the resonance, but the coefficient is a periodic function of ln(a) that may have resonant enhancement at values of a that differ by multiples of 22.7.

cond-mat.other↗

arXiv2004

The Renormalization Group Limit Cycle for the 1/r^2 Potential

Previous work has shown that if an attractive 1/r^2 potential is regularized at short distances by a spherical square-well potential, renormalization allows multiple solutions for the depth of the square well. The depth can be chosen to be a continuous function of the short-distance cutoff R, but it can also be a log-periodic function of R with finite discontinuities, corresponding to a renormalization group (RG) limit cycle. We consider the regularization with a delta-shell potential. In this case, the coupling constant is uniquely determined to be a log-periodic function of R with infinite discontinuities, and an RG limit cycle is unavoidable. In general, a regularization with an RG limit cycle is selected as the correct renormalization of the 1/r^2 potential by the conditions that the cutoff radius R can be made arbitrarily small and that physical observables are reproduced accurately at all energies much less than hbar^2/mR^2.

hep-th↗

arXiv2003

Low-energy Universality and the New Charmonium Resonance at 3870 MeV

The recently-discovered narrow charmonium resonance near 3870 MeV is interpreted as a hadronic molecule whose constituents are the charm mesons D^0 and \bar D^{*0} or \bar D^0 and D^{*0}. Because of an accidental fine-tuning of the molecule to very near the D^0 \bar D^{*0} threshold, it has some universal properties that are completely determined by the unnaturally large D^0 \bar D^{*0} scattering length a. Its narrow width can be explained by the suppression by a factor of 1/a of decay modes other than the decay of a constituent \bar D^{*0} or D^{*0}. Its production rates are also suppressed by a factor of 1/a. A particularly predictive mechanism for generating the large scattering length is the accidental fine-tuning of a P-wave charmonium state to the D^0 \bar D^{*0} threshold.

hep-ph↗

arXiv2003

An Infrared Renormalization Group Limit Cycle in QCD

We conjecture that QCD can be tuned to an infrared limit cycle in the three-nucleon system by adjusting the up and down quark masses to critical values at which the binding energies of the deuteron and its spin-singlet partner are tuned to zero. At the critical point, the triton would have infinitely many arbitrarily-shallow excited states with the ratio of the binding energies of successive states approaching a universal constant close to 515.

nucl-th↗

arXiv2003

Efimov States in a Bose-Einstein Condensate near a Feshbach Resonance

Recent experiments with Bose-Einstein condensates of 85Rb atoms near a Feshbach resonance have produced evidence for a condensate of diatomic molecules coexisting with the atom condensate. It should also be possible to create condensates of the triatomic molecules predicted by Efimov coexisting with the atom and dimer condensates. The smoking gun for the trimer condensate would be oscillatory dependence of observables on the binding energy of the trimer. It may also be possible to deduce the existence of the trimer condensate from the spectra of the bursts of atoms and dimers created in the disappearance of the trimers.

cond-mat↗

arXiv2003

Lambda_c^+/Lambda_c^- Asymmetry in Hadroproduction from Heavy-Quark Recombination

Asymmetries in the hadroproduction of charm particles directly probe power corrections to the QCD factorization theorems. In this paper, the heavy-quark recombination mechanism, a power correction that explains charm meson asymmetries, is extended to charm baryons. In this mechanism, a light quark participates in the hard scattering that creates a charm quark and they hadronize together into a charm baryon. This provides a natural and economical explanation for the Λ_c^+/Λ_c^- asymmetries measured in πN and p N collisions.

hep-ph↗

arXiv2003

An Infrared Renormalization Group Limit Cycle in QCD

Small increases in the up and down quark masses of QCD would tune the theory to the critical renormalization group trajectory for an infrared limit cycle in the three-nucleon system. At critical values of the quark masses, the deuteron binding energy goes to zero and the triton has infinitely many excited states with an accumulation point at the 3-nucleon threshold. The ratio of the binding energies of successive states approaches a universal constant that is close to 515. The proximity of physical QCD to the critical trajectory for this limit cycle explains the success of an effective field theory of nucleons with contact interactions only in describing the low-energy 3-nucleon system.

nucl-th↗

arXiv2003

Universal Equation for Efimov States

Efimov states are a sequence of shallow 3-body bound states that arise when the 2-body scattering length is large. Efimov showed that the binding energies of these states can be calculated in terms of the scattering length and a 3-body parameter by solving a transcendental equation involving a universal function of one variable. We calculate this universal function using effective field theory and use it to describe the three-body system of 4He atoms. We also extend Efimov's theory to include the effects of deep 2-body bound states, which give widths to the Efimov states.

cond-mat↗

arXiv2003

Universality in the Three-Body Problem for 4He Atoms

The two-body scattering length a for 4He atoms is much larger than their effective range r_s. As a consequence, low-energy few-body observables have universal characteristics that are independent of the interaction potential. Universality implies that, up to corrections suppressed by r_s/a, all low-energy three-body observables are determined by a and a three-body parameter Λ_*. We give simple expressions in terms of a and Λ_* for the trimer binding energy equation, the atom-dimer scattering phase shifts, and the rate for three-body recombination at threshold. We determine Λ_* for several 4He potentials from the calculated binding energy of the excited state of the trimer and use it to obtain the universality predictions for the other low-energy observables. We also use the calculated values for one potential to estimate the effective range corrections for the other potentials.

cond-mat↗

arXiv2003

Comment on ``Ramsey Fringes in a Bose-Einstein Condensate between Atoms and Molecules''

In Phys. Rev. Lett. 89, 180401 (2002) [cond-mat/0204504], Kokkelmans and Holland interpret the results of a recent experiment at JILA that demonstrated atom-molecule coherence in a Bose-Einstein condensate. Using a mean-field approximation to a resonance field theory involving an atom condensate and a molecular condensate, they find that the molecular condensate is tiny compared to the atom condensate. We show that if the probability for the molecular field to create a diatomic molecule is correctly included, the numbers of atoms in the atom condensate and in the condensate of diatomic molecules are comparable.

cond-mat↗

arXiv2002

Convergence of the Linear Delta Expansion in the Critical O(N) Field Theory

The linear delta expansion is applied to the 3-dimensional O(N) scalar field theory at its critical point in a way that is compatible with the large-N limit. For a range of the arbitrary mass parameter, the linear delta expansion for converges, with errors decreasing like a power of the order n in delta. If the principal of minimal sensitivity is used to optimize the convergence rate, the errors seem to decrease exponentially with n.

hep-ph↗

arXiv2002

On the Convergence of the Linear Delta Expansion for the Shift in T_c for Bose-Einstein Condensation

The leading correction from interactions to the transition temperature T_c for Bose-Einstein condensation can be obtained from a nonperturbative calculation in the critical O(N) scalar field theory in 3 dimensions with N=2. We show that the linear delta expansion can be applied to this problem in such a way that in the large-N limit it converges to the exact analytic result. If the principal of minimal sensitivity is used to optimize the convergence rate, the errors seem to decrease exponentially with the order in the delta expansion. For N=2, we calculate the shift in T_c to fourth order in delta. The results are consistent with slow convergence to the results of recent lattice Monte Carlo calculations.

cond-mat↗

arXiv2002

Charm-Anticharm Asymmetries in Photoproduction from Heavy-Quark Recombination

The asymmetries between charm and anticharm mesons observed in fixed-target photoproduction experiments are an order of magnitude larger than the asymmetries predicted by conventional perturbative QCD. We show that these charm meson asymmetries can be explained by a heavy-quark recombination mechanism for heavy meson production. In this process, a charm quark combines with a light antiquark from the hard-scattering process and they subsequently hadronize into a state including the charm meson. This recombination mechanism can be calculated within perturbative QCD up to some nonperturbative constants. After using symmetries of QCD to reduce the number of free parameters to two, we obtain a good fit to all the data on the asymmetries for charmed mesons from the E687 and E691 experiments.

hep-ph↗

arXiv2002

B Production Asymmetries in Perturbative QCD

This paper explores a new mechanism for B production in which a b quark combines with a light parton from the hard-scattering process before hadronizing into the B hadron. This recombination mechanism can be calculated within perturbative QCD up to a few nonperturbative constants. Though suppressed at large transverse momentum by a factor Lambda_QCD m_b/p_t^2 relative to b quark fragmentation production, it can be important at large rapidities. A signature for this heavy-quark recombination mechanism in proton-antiproton colliders is the presence of rapidity asymmetries in B cross sections. Given reasonable assumptions about the size of nonperturbative parameters entering the calculation, we find that the asymmetries are only significant for rapidities larger than those currently probed by collider experiments.

hep-ph↗

arXiv2002

The Leading Particle Effect from Heavy-Quark Recombination

The leading particle effect in charm hadroproduction is an enhancement of the cross section for a charmed hadron D in the forward direction of the beam when the beam hadron has a valence parton in common with the D. The large D+/D- asymmetry observed by the E791 experiment is an example of this phenomenon. We show that the heavy-quark recombination mechanism provides an economical explanation for this effect. In particular, the D+/D- asymmetry can be fit reasonably well using a single parameter whose value is consistent with a recent determination from charm photoproduction.

hep-ph↗

arXiv2002

HTL Perturbation Theory to Two Loops

We calculate the pressure for pure-glue QCD at high temperature to two-loop order using hard-thermal-loop (HTL) perturbation theory. At this order, all the ultraviolet divergences can be absorbed into renormalizations of the vacuum energy density and the HTL mass parameter. We determine the HTL mass parameter by a variational prescription. The resulting predictions for the pressure fail to agree with results from lattice gauge theory at temperatures for which they are available.

hep-ph↗

arXiv2002

The Dilute Bose-Einstein Condensate with Large Scattering Length

We study a dilute Bose gas of atoms whose scattering length a is large compared to the range of their interaction. We calculate the energy density of the homogeneous Bose-Einstein condensate to second order in the low-density expansion, expressing it in terms of a and a second parameter Lambda_* that determines the low-energy observables in the 3-body sector. The second-order correction to the energy density has a small imaginary part that reflects the instability due to 3-body recombination. In the case of a trapped Bose-Einstein condensate with large negative scattering length, we calculate the coefficient of the 3-body mean-field term in the energy density in terms of a and Lambda_*. It can be very large if there is an Efimov state near threshold.

cond-mat↗