Instantons and the Ground State of the Massive Schwinger Model

We study the massive Schwinger model, quantum electrodynamics of massive, Dirac fermions, in 1+1 dimensions; with space compactified to a circle. In the limit that transitions to fermion--anti-fermion pairs can be neglected, we study the full ground state. We focus on the effect of instantons which mediate tunnelling transitions in the induced potential for the dynamical degree of freedom in the gauge field.Comment: 17 pages, plain te

Quantum Transition State Theory for proton transfer reactions in enzymes

We consider the role of quantum effects in the transfer of hyrogen-like species in enzyme-catalysed reactions. This study is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects imply that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We use a path integral approach which provides a general framework to understand tunneling in a quantum system which interacts with an environment at non-zero temperature. Here the quantum system is the active site of the enzyme and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature $T_0$ which is determined by the curvature of potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. For physically reasonable parameters quantum transition state theory gives a quantitative description of the temperature dependence and magnitude of kinetic isotope effects for two classes of enzymes which have been claimed to exhibit signatures of quantum tunneling. The only quantum effects are those associated with the transition state, both reflection at the barrier top and tunneling just below the barrier. We establish that the friction due to the environment is weak and only slightly modifies the reaction rate. Furthermore, at room temperature and for typical energy barriers environmental degrees of freedom with frequencies much less than 1000 cm$^{-1}$ do not have a significant effect on quantum corrections to the reaction rate.Comment: Aspects of the article are discussed at condensedconcepts.blogspot.co

Amelioration of ocean acidification and warming effects through physiological buffering of a macroalgae

Concurrent anthropogenic global climate change and ocean acidification are expected to have a negative impact on calcifying marine organisms. While knowledge of biological responses of organisms to oceanic stress has emerged from single-species experiments, these do not capture ecologically relevant scenarios where the potential for multi-organism physiological interactions is assessed. Marine algae provide an interesting case study, as their photosynthetic activity elevates pH in the surrounding microenvironment, potentially buffering more acidic conditions for associated epiphytes. We present findings that indicate increased tolerance of an important epiphytic for aminifera, Marginopora vertebralis, to the effects of increased temperature (+/- 3 degrees C) and p CO2(similar to 1,000 mu atm) when associated with its common algal host, Laurencia intricata. Specimens of M. vertebralis were incubated for 15 days in flow-through aquaria simulating current and end-of-century temperature and pH conditions. Physiological measures of growth (change in wet weight), calcification (measured change in total alkalinity in closed bottles), photochemical efficiency (Fv/Fm), total chlorophyll, photosynthesis (oxygen flux), and respiration were determined. When incubated in isolation,M. vertebralis-exhibited reduced growth in end-of-century projections of ocean acidification conditions, while calcification rates were lowest in the high-temperature, low-pH treatment. Interestingly, association with L. intricata ameliorated these stress effects with the growth and calcification rates ofM. vertebralis being similar to those observed in ambient conditions. Total chlorophyll levels in M. vertebral is decreased when in association with L. intricata, while maximum photochemical efficiency increased in ambient conditions. Net production estimates remained similar between M. vertebralis in isolation and in association with L. intricata, although both production and respiration rates ofM. vertebralis were significantly higher when associated with L. intricata. These results indicate that the association with L. intricata increases the resilience ofM. vertebralis to climate change stress, providing one of the first examples of physiological buffering by a marine alga that can ameliorate the negative effects of changing ocean conditions

Paternal Mitochondrial Transmission in Intra-Species \u3ci\u3eCaenorhabditis briggsae\u3c/i\u3e Hybrids

To study mitochondrial-nuclear genetic interactions in the nematode Caenorhabditis briggsae, our three laboratories independently created 38 intra-species cytoplasmic-nuclear hybrid (cybrid) lines. Although the cross design combines maternal mitotypes with paternal nuclear genotypes, eight lines (21%) unexpectedly contained paternal mitotypes. All eight share in common ancestry of one of two genetically related strains. This unexpected parallel observation of paternal mitochondrial transmission, undesirable given our intent of creating cybrids, provides a serendipitous experimental model and framework to study the molecular and evolutionary basis of uniparental mitochondrial inheritance

Duality between Electric and Magnetic Black Holes

A number of attempts have recently been made to extend the conjectured $S$ duality of Yang Mills theory to gravity. Central to these speculations has been the belief that electrically and magnetically charged black holes, the solitons of quantum gravity, have identical quantum properties. This is not obvious, because although duality is a symmetry of the classical equations of motion, it changes the sign of the Maxwell action. Nevertheless, we show that the chemical potential and charge projection that one has to introduce for electric but not magnetic black holes exactly compensate for the difference in action in the semi-classical approximation. In particular, we show that the pair production of electric black holes is not a runaway process, as one might think if one just went by the action of the relevant instanton. We also comment on the definition of the entropy in cosmological situations, and show that we need to be more careful when defining the entropy than we are in an asymptotically-flat case.Comment: 23 pages, revtex, no figures. Major revision: two sections on the electric Ernst solution adde

Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability

Using Sloan Digital Sky Survey (SDSS) quasar spectra taken at multiple epochs, we find that the composite flux density differences in the rest frame wavelength range 1300-6000 AA can be fit by a standard thermal accretion disk model where the accretion rate has changed from one epoch to the next (without considering additional continuum emission components). The fit to the composite residual has two free parameters: a normalizing constant and the average characteristic temperature $\bar{T}^*$. In turn the characteristic temperature is dependent on the ratio of the mass accretion rate to the square of the black hole mass. We therefore conclude that most of the UV/optical variability may be due to processes involving the disk, and thus that a significant fraction of the UV/optical spectrum may come directly from the disk.Comment: 31 pages, 8 figure

Patching up the No-Boundary Proposal with virtual Euclidean wormholes

In quantum cosmology, one often considers tunneling phenomena which may have occurred in the early universe. Processes requiring quantum penetration of a potential barrier include black hole pair creation and the decay of vacuum domain walls. Ideally, one calculates the rates for such processes by finding an instanton, or Euclidean solution of the field equations, which interpolates between the initial and final states. In practice, however, it has become customary to calculate such amplitudes using the No-Boundary Proposal of Hartle and Hawking. A criticism of this method is that it does not use a single path which interpolates between the initial and final states, but two disjoint instantons: One divides the probability to create the final state from nothing by the probability to create the initial state from nothing and decrees the answer to be the rate of tunneling from the initial to the final state. Here, we demonstrate the validity of this approach by constructing continuous paths connecting the ingoing and outgoing data, which may be viewed as perturbations of the set of disconnected instantons. They are off-shell, but will still dominate the path integral as they have action arbitrarily close to the no-boundary action. In this picture, a virtual domain wall, or wormhole, is created and annihilated in such a way as to interface between the disjoint instantons. Decay rates calculated using our construction differ from decay rates calculated using the No-Boundary Proposal only in the prefactor; the exponent, which usually dominates the result, remains unchanged.Comment: 23 pages REVTeX plus 7 figure

Black Hole Pair Creation and the Entropy Factor

It is shown that in the instanton approximation the rate of creation of black holes is always enhanced by a factor of the exponential of the black hole entropy relative to the rate of creation of compact matter distributions (stars). This result holds for any generally covariant theory of gravitational and matter fields that can be expressed in Hamiltonian form. It generalizes the result obtained previously for the pair creation of magnetically charged black holes by a magnetic field in Einstein--Maxwell theory. The particular example of pair creation of electrically charged black holes by an electric field in Einstein--Maxwell theory is discussed in detail.Comment: (12 pages, ReVTeX) Revised version of "Pair Creation of Electrically Charged Black Holes". New section shows that the BH pair creation rate is enhanced by a factor $\exp(BH entropy)$ for any Hamiltonian gravity + matter theor

Top Radiative Corrections in Non-minimal Standard Models

We derive the one-loop effective action induced by a heavy top in models with an extended Higgs sector. We use the effective action to analyze the top corrections to the $\rho$ parameter and to the Higgs-gauge boson couplings. We show that in models with $\rho\not=1$ at tree-level, one does not lose generally the bound on $m_t$ from the $\rho$ parameter.Comment: 9 pages, phyzzx file, UPR-0603T. (a new reference has been added

Quantum Pair Creation of Soliton Domain Walls

A large body of experimental evidence suggests that the decay of the false vacuum, accompanied by quantum pair creation of soliton domain walls, can occur in a variety of condensed matter systems. Examples include nucleation of charge soliton pairs in density waves [eg. J. H. Miller, Jr. et al., Phys. Rev. Lett. 84, 1555 (2000)] and flux soliton pairs in long Josephon junctions. Recently, Dias and Lemos [J. Math. Phys. 42, 3292 (2001)] have argued that the mass $m$ of the soliton should be interpreted as a line density and a surface density, respectively, for (2+1)-D and (3+1)-D systems in the expression for the pair production rate. As the transverse dimensions are increased and the total mass (energy) becomes large, thermal activation becomes suppressed, so quantum processes can dominate even at relatively high temperatures. This paper will discuss both experimental evidence and theoretical arguments for the existence of high-temperature collective quantum phenomena