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Publication Classical physics and quantum loops(2004-01-01) Holstein, BR; Donoghue, JFThe standard picture of the loop expansion associates a factor of ¯h with each loop, suggesting that the tree diagrams are to be associated with classical physics, while loop effects are quantum mechanical in nature. We discuss examples wherein classical effects arise from loop contributions and display the relationship between the classical terms and the long range effects of massless particles.Publication Sigma exchange in the nuclear force and effective field theory(2006-01-01) Donoghue, JFIn the phenomenological description of the nuclear interaction an important role is traditionally played by the exchange of a scalar I=0 meson, the sigma, of mass 500–600 MeV, which however is not seen clearly in the particle spectrum and which has a very ambiguous status in QCD. I show that a remarkably simple and reasonably controlled combination of ingredients can reproduce the features of this part of the nuclear force. The use of chiral perturbation theory calculations for two pion exchange supplemented by the Omnes function for pion rescattering suffices to reproduce the magnitude and shape of the exchange of a supposed σ particle. I also attempt to relate this description to the contact interaction that enters more modern descriptions of the internucleon interaction.Publication Quark and lepton masses and mixing in the landscape(2006-01-01) Donoghue, JF; Dutta, K; Ross, AEven if quark and lepton masses are not uniquely predicted by the fundamental theory, as may be the case in the string theory landscape, nevertheless their pattern may reveal features of the underlying theory. We use statistical techniques to show that the observed masses appear to be representative of a scale-invariant distribution, ρ(m)∼1/m. If we extend this distribution to include all the Yukawa couplings, we show that the resulting Cabibbo-Kobayashi-Maskawa matrix elements typically show a hierarchical pattern similar to observations. The Jarlskog invariant measuring the amount of CP violation is also well reproduced in magnitude. We also apply this framework to neutrinos using the seesaw mechanism. The neutrino results are ambiguous, with the observed pattern being statistically allowed even though the framework does not provide a natural explanation for the observed two large mixing angles. Our framework highly favors a normal hierarchy of neutrino masses. We also are able to make statistical predictions in the neutrino sector when we specialize to situations consistent with the known mass differences and two large mixing angles. Within our framework, we show that with 95% confidence the presently unmeasured Maki-Nakagawa-Sakata mixing angle sinθ13 is larger than 0.04 and typically of order 0.1. The leptonic Jarlskog invariant is found to be typically of order 10-2 and the magnitude of the effective Majorana mass mee is typically of order 0.001 eV.Publication Isotropy of the early universe from CMB anisotropies(2005-01-01) Donoghue, EP; Donoghue, JFThe acoustic peak in the cosmic microwave background power spectrum is sensitive to causal processes and cosmological parameters in the early universe up to the time of last scattering. We provide limits on correlated spatial variations of the peak height and peak position and interpret these as constraints on the spatial variation of the cosmological parameters (baryon density, cold dark matter density, and cosmological constant as well as the amplitude and tilt of the original fluctuations). We utilize recent work of Hansen, Banday, and Górski who have studied the spatial isotropy of the power spectrum as measured by WMAP by performing the power spectrum analysis on smaller patches of the sky. We find that there is no statistically significant correlated asymmetry of the peak. Hansen, Banday, and Górski have also provided preliminary indications of a preferred direction in the lower angular momentum range (ℓ∼2–40) and we show how possible explanations of this asymmetry are severely constrained by the data on the acoustic peak. Finally we show a possible non-Gaussian feature in the data, associated with a difference in the northern and southern galactic hemispheres.Publication Nuclear central force in the chiral limit(2006-01-01) Donoghue, JFChiral perturbation theory supplemented by the Omnes function is employed to study the strength of the isoscalar central nuclear interaction, GS, in the chiral limit vs the physical case. A very large modification is seen, i.e., ηs=GS chiral/GS physical=1.37±0.10. This large effect is seen to arise dominantly at low energy from the extra contributions made by massless pions at energies near the physical threshold where the physical spectral function must vanish kinematically. The slope away from the chiral limit, dS, is also calculated and is correspondingly large. I also explain why this large variation is to be expected.Publication Parametrization dependence of the energy-momentum tensor and the metric(2007-01-01) Bjerrum-Bohr, NEJ; Donoghue, JF; Holstein, BRWe use results by Kirilin to comment that in general relativity the nonleading terms in the energy-momentum tensor of a particle depends on the parameterization of the gravitational field. The classical observables are parameterization independent after a change in coordinates. The quantum effects that emerge within the same calculation of the metric also depend on the parameterization and a full quantum calculation requires the inclusion of further diagrams. However, within a given parameterization the quantum effects calculated by us in a previous paper are well defined. Flaws of Kirilin’s proposed alternate metric definition are described and we explain why the diagrams that we calculated are the appropriate ones.Publication Gauge federation as an alternative to unification(2009-01-01) Donoghue, JF; Pais, PWe motivate and explore the possibility that extra SU(N) gauge groups may exist independently of the Standard Model groups, yet not be subgroups of some grand unified group. We study the running of the coupling constants as a potential evidence for a common origin of all the gauge theories. Several different example are displayed. Some of the multiple options involve physics at the TeV scale.Publication Constraints on the variability of quark masses from nuclear binding(2008-01-01) Damour, T; Donoghue, JFBased on recent work on nuclear binding, we update and extend the anthropic constraints on the light quark masses, with results that are more tightly constrained than previously obtained. We find that heavy nuclei would fall apart (because the attractive nuclear central potential becomes too weak) if the sum of the light quark masses mu + md would exceed their physical values by 64% (at 95% confidence level). We summarize the anthropic constraints that follow from requiring the existence both of heavy atoms and of hydrogen. With the additional assumption that the quark Yukawa couplings do not vary, these constraints provide a remarkably tight anthropic window for the Higgs vacuum expectation value: 0.39 < v/vphysical < 1.64.Publication Remarks on the minimal vectorial standard model(2009-01-01) Anber, Mohamed M.; Aydemir, Ufuk; Donoghue, John F.; Pais, PreemaWe explore the available parameter space of the minimal vectorial standard model. In this theory, the gauge currents are initially vectorial but the Higgs sector produces chiral mass eigenstates, leading to a set of heavy right-handed mirror particles. We describe the phenomenology of the residual parameter space and suggest that the model will be readily tested at the LHC.Publication Nonisotropy in the CMB power spectrum in single field inflation(2009-01-01) Donoghue, JF; Dutta, K; Ross, AContaldi et al. [C. R. Contaldi, M. Peloso, L. Kofman, and A. Linde, J. Cosmol. Astropart. Phys. 07 (2003) 002] have suggested that an initial period of kinetic energy domination in single field inflation may explain the lack of CMB power at large angular scales. We note that in this situation it is natural that there also be a spatial gradient in the initial value of the inflaton field, and that this can provide a spatial asymmetry in the observed CMB power spectrum, manifest at low values of ℓ. We investigate the nature of this asymmetry and comment on its relation to possible anomalies at low ℓ.Publication Generalized Polarizabilities and the Chiral Structure of the Nucleon(1997-09-25) Hemmert, Thomas R.; Holstein, Barry R.; Knöchlein, Germar; Scherer, StefanPublication Regge kinematics in soft collinear effective theory(2010-01-01) Donoghue, JF; Wyler, DWe discuss the kinematics of the particles that make up a Reggeon in field theory, using the terminology of the soft collinear effective theory (SCET). Reggeization sums a series of strongly ordered collinear emissions resulting in an overall Reggeon exchange that falls in the Glauber or Coulomb kinematic region. This is an extremely multiscale problem and appears to fall outside of the usual organizing scheme of SCET.Publication Breaking diffeomorphism invariance and tests for the emergence of gravity(2010-01-01) Anber, MM; Aydemir, U; Donoghue, JFIf general relativity is an emergent phenomenon, there may be small violations of diffeomorphism invariance. We propose a phenomenology of perturbatively small violations of general relativity by the inclusion of terms which break general covariance. These can be tested by matching to the Parameterized Post Newtonian (PPN) formalism. The most sensitive tests involve pulsar timing and provide an extremely strong bound, with a dimensionless constraint of order 10−20 relative to gravitational strength.Publication Likely values of the Higgs vacuum expectation value(2010-01-01) Donoghue, JF; Dutta, K; Ross, A; Tegmark, MWe make an estimate of the likelihood function for the Higgs vacuum expectation value (vev) by imposing anthropic constraints on the existence of atoms while allowing the other parameters of the standard model to also be variable. We argue that the most important extra ingredients are the Yukawa couplings, and for the intrinsic distribution of Yukawa couplings we use the scale-invariant distribution which is favored phenomenologically. The result is successful phenomenologically, favoring values close to the observed vev. We also discuss modifications that can change these conclusions. Our work supports the hypothesis that the anthropic constraints could be the origin of the small Higgs vev.Publication Theory of motional inhibition of interlayer quantum tunneling in thin^{3}He films(1980) Mullin, WJ; Landesmant, A.An attempt is made to interpret NMR data on 3He films for coverages just over one monolayer in terms of motion due to the quantum exchange of particles between layers. A summary of the relevant data and of various possible relaxation mechanisms is given and it is found that a portion of the data seems amenable to an interlayer exchange interpretation. The detailed theory of this process requires the use of the exchange operator concept and a Kubo-theory treatment of the effect of second-layer motion on the exchange process. It is shown that the ldquobarerdquo interlayer exchange process characterized by constant J 12 is slowed by second-layer translational motion so that the effective exchange parameter becomes \~J 12 ap J 12 2/epsiv2, where epsiv2 is a second-layer single-particle translational energy. In order to fit the NMR data it is found that epsiv2 must be evaluated in the classical limit rather than the degenerate Fermi limit, and that \~J 12 ap J 11, the exchange energy within the first-layer solid. These conditions require a helium second-layer effective mass of m * > 5m and J 12>600J 11, which are anomously large values for thesePublication Phenomenology of the equivalence principle with light scalars(2010-01-01) Damour, T; Donoghue, JFLight scalar particles with couplings of sub-gravitational strength, which can generically be called 'dilatons', can produce violations of the equivalence principle. However, in order to understand experimental sensitivities one must know the coupling of these scalars to atomic systems. We report here on a study of the required couplings. We give a general Lagrangian with five independent dilaton parameters and calculate the 'dilaton charge' of atomic systems for each of these. Two combinations are particularly important. One is due to the variations in the nuclear binding energy, with a sensitivity scaling with the atomic number as A−1/3. The other is due to electromagnetism. We compare limits on the dilaton parameters from existing experiments.Publication BOSE CONDENSATION OF IDEALIZED SPIN-POLARIZED ATOMIC-HYDROGEN IN EQUILIBRIUM(1980) Mullin, WJA model of spin-polarized hydrogen (H↑) is treated in which interactions between atoms are neglected while the single-atom Zeeman and hyperfine interactions are treated exactly. These magnetic terms in the Hamiltonian are found to affect substantially the Bose-Einstein condensation and the various thermodynamic variables. Computations are discussed of the condensation temperature, condensate density, and specific heat in order to indicate how changes in magnetic field strength might be expected to affect future measurements on this quantum system.Publication OBSERVATION OF SPIN ROTATION EFFECTS IN POLARIZED HE-3-HE-4 MIXTURES(1984) GULLY, WJ; Mullin, WJQuantum exchange effects, predicted to occur in the spin diffusion of polarized nondegenerate gases, have been observed in a 3He-4He mixture by spin-echo techniques. Measurements of the spin rotation parameter (μM0)2 and diffusion constant D are in reasonable agreement with theoretical predictions until the degeneracy temperature is approached.Publication EXACT TRANSPORT-PROPERTIES OF DEGENERATE, WEAKLY INTERACTING, AND SPIN-POLARIZED FERMIONS(1983) Mullin, WJ; MIYAKE, KExact results for the transport coefficients of a highly degenerate spin-polarized Fermi system are presented. The case of weakly interacting particles, such as dilute3He in4He or D darr, is treated. The results are compared to the variational treatment and corrections as large as 8% are found. Detailed behavior of the polarization of an ideal Fermi gas as a function of temperature and magnetic field is discussed as a model for dilute3He in4He. Limits of applicability of the formulas are given. We find that at appropriate fields and temperatures, the two spin species may be considered to be a mixture of a degenerate and a classical gas.Publication Molecular-dynamics Simulations of Stacking-fault-induced Dislocation Annihilation in Pre-strained Ultrathin Single-crystalline Copper Films(2009-01-01) Kolluri, Kedarnath; Gungor, M. Rauf; Maroudas, DimitriosWe report results of large-scale molecular-dynamics (MD) simulations of dynamic deformation under biaxial tensile strain of pre-strained single-crystalline nanometerscale- thick face-centered cubic (fcc) copper films. Our results show that stacking faults, which are abundantly present in fcc metals, may play a significant role in the dissociation, cross-slip, and eventual annihilation of dislocations in small-volume structures of fcc metals. The underlying mechanisms are mediated by interactions within and between extended dislocations that lead to annihilation of Shockley partial dislocations or formation of perfect dislocations. Our findings demonstrate dislocation starvation in small-volume structures with ultra-thin film geometry, governed by a mechanism other than dislocation escape to free surfaces, and underline the significant role of geometry in determining the mechanical response of metallic small-volume structures.