Polyamorphism of ice at low temperatures from constant-pressure simulations

We report results of MD simulations of amorphous ice in the pressure range 0 - 22.5 kbar. The high-density amorphous ice (HDA) prepared by compression of Ih ice at T = 80 K is annealed to T = 170 K at intermediate pressures in order to generate relaxed states. We confirm the existence of recently observed phenomena, the very high-density amorphous ice and a continuum of HDA forms. We suggest that both phenomena have their origin in the evolution of the network topology of the annealed HDA phase with decreasing volume, resulting at low temperatures in the metastability of a range of densities.Comment: 11 pages, 5 postscript figures. To be published in Physical Review Letter

Strong IR Cancellation in Heavy Quarkonium and Precise Top Mass Determination

Combining recent perturbative analyses on the static QCD potential and the quark pole mass, we find that, for the heavy quarkonium states $c\bar{c}$, $b\bar{b}$ and $t\bar{t}$, (1) ultra-soft (US) corrections in the binding energies are small, and (2) there is a stronger cancellation of IR contributions than what has been predicted by renormalon dominance hypothesis. By contrast, for a hypothetical heavy quarkonium system with a small number of active quark flavors ($n_l\approx 0$), we observe evidence that renormalon dominance holds accurately and that non-negligible contributions from US corrections exist. In addition, we examine contributions of renormalons at $u=- 1$. As an important consequence, we improve on a previous prediction for possible achievable accuracy of top quark $\overline{\rm MS}$--mass measurement at a future linear collider and estimate that in principle 20--30~MeV accuracy is reachable.Comment: 17 pages, 7 figures, 3 tables; Revisions in ver.2: We added (i) a more conservative error estimate of m_t determination, (ii) discussion on u=+1 and u=-1 renormalons, (iii) interpretation of PS-schem

Relation between the High Density Phase and the Very-High Density Phase of Amorphous Solid Water

It has been suggested that high-density amorphous (HDA) ice is a structurally arrested form of high-density liquid (HDL) water, while low-density amorphous (LDA) ice is a structurally arrested form of low-density liquid (LDL) water. Recent experiments and simulations have been interpreted to support the possibility of a second "distinct" high-density structural state, named very high-density amorphous (VHDA) ice, questioning the LDL-HDL hypothesis. We test this interpretation using extensive computer simulations, and find that VHDA is a more stable form of HDA and that in fact VHDA should be considered as the amorphous ice of the quenched HDL.Comment: 5 pages, 4 fig

Ice XII in its second regime of metastability

We present neutron powder diffraction results which give unambiguous evidence for the formation of the recently identified new crystalline ice phase[Lobban et al.,Nature, 391, 268, (1998)], labeled ice XII, at completely different conditions. Ice XII is produced here by compressing hexagonal ice I_h at T = 77, 100, 140 and 160 K up to 1.8 GPa. It can be maintained at ambient pressure in the temperature range 1.5 < T < 135 K. High resolution diffraction is carried out at T = 1.5 K and ambient pressure on ice XII and accurate structural properties are obtained from Rietveld refinement. At T = 140 and 160 K additionally ice III/IX is formed. The increasing amount of ice III/IX with increasing temperature gives an upper limit of T ~ 150 K for the successful formation of ice XII with the presented procedure.Comment: 3 Pages of RevTeX, 3 tables, 3 figures (submitted to Physical Review Letters

Amorphous-amorphous transition and the two-step replica symmetry breaking phase

The nature of polyamorphism and amorphous-to-amorphous transition is investigated by means of an exactly solvable model with quenched disorder, the spherical s+p multi-spin interaction model. The analysis is carried out in the framework of Replica Symmetry Breaking theory and leads to the identification of low temperature glass phases of different kinds. Besides the usual `one-step' solution, known to reproduce all basic properties of structural glasses, also a physically consistent `two-step' solution arises. More complicated phases are found as well, as temperature is further decreased, expressing a complex variety of metastable states structures for amorphous systems.Comment: 8 pages, 7 figures, longer version, new references adde

Structural Order in Glassy Water

We investigate structural order in glassy water by performing classical molecular dynamics simulations using the extended simple point charge (SPC/E) model of water. We perform isochoric cooling simulations across the glass transition temperature at different cooling rates and densities. We quantify structural order by orientational and translational order metrics. Upon cooling the liquid into the glassy state, both the orientational order parameter $Q$ and translational order parameter $\tau$ increase. At T=0 K, the glasses fall on a line in the $Q$-$\tau$ plane or {\it order map}. The position of this line depends only on density and coincides with the location in the order map of the inherent structures (IS) sampled upon cooling. We evaluate the energy of the IS, $e_{IS}(T)$, and find that both order parameters for the IS are proportional to $e_{IS}$. We also study the structural order during the transformation of low-density amorphous ice (LDA) to high-density amorphous ice (HDA) upon isothermal compression and are able to identify distinct regions in the order map corresponding to these glasses. Comparison of the order parameters for LDA and HDA with those obtained upon isochoric cooling indicates major structural differences between glasses obtained by cooling and glasses obtained by compression. These structural differences are only weakly reflected in the pair correlation function. We also characterize the evolution of structural order upon isobaric annealing, leading at high pressure to very-high density amorphous ice (VHDA).Comment: submitte

Possible complex annihilation and B -> K pi direct CP asymmetry

We point out that a sizable strong phase could be generated from the penguin annihilation in the soft-collinear effective theory for B meson decays. Keeping a small scale suppressed by O(Lambda/m_b), Lambda being a hadronic scale and m_b the b quark mass, in the denominators of internal particle propagators without expansion, the resultant strong phase can accommodate the data of the B^0 -> K^-+ pi^+- direct CP asymmetry. Our study reconciles the opposite conclusions on the real or complex penguin annihilation amplitude drawn in the soft-collinear effective theory and in the perturbative QCD approach based on k_T factorization theorem.Comment: 8 pages, 1 figure, added reference

Interplay Between Time-Temperature-Transformation and the Liquid-Liquid Phase Transition in Water

We study the TIP5P water model proposed by Mahoney and Jorgensen, which is closer to real water than previously-proposed classical pairwise additive potentials. We simulate the model in a wide range of deeply supercooled states and find (i) the existence of a non-monotonic ``nose-shaped'' temperature of maximum density line and a non-reentrant spinodal, (ii) the presence of a low temperature phase transition, (iii) the free evolution of bulk water to ice, and (iv) the time-temperature-transformation curves at different densities.Comment: RevTeX4, 4 pages, 4 eps figure

Simple Fluids with Complex Phase Behavior

We find that a system of particles interacting through a simple isotropic potential with a softened core is able to exhibit a rich phase behavior including: a liquid-liquid phase transition in the supercooled phase, as has been suggested for water; a gas-liquid-liquid triple point; a freezing line with anomalous reentrant behavior. The essential ingredient leading to these features resides in that the potential investigated gives origin to two effective core radii.Comment: 7 pages including 3 eps figures + 1 jpeg figur