123 research outputs found
On Black Hole Stability in Critical Gravities
We consider extended cosmological gravities with Ricci tensor and scalar
squared terms in diverse dimensions. These theories admit solutions of Einstein
metrics, including the Schwarzschild-Tangherlini AdS black holes, whose mass
and entropy vanish at the critical point. We perform linearized analysis around
the black holes and show that in general the spectrum consists of the usual
spin-2 massless and ghost massive modes. We demonstrate that there is no
exponentially-growing tachyon mode in the black holes. At the critical point,
the massless spin-2 modes have zero energy whilst the massive spin-2 modes are
replaced by the log modes. There always exist certain linear combination of
massless and log modes that has negative energy. Thus the stability of the
black holes requires that the log modes to be truncated out by the boundary
condition.Comment: 16 pages, minor corrections, further comments and references adde
Bondi-Sachs metrics and Photon Rockets
We study the Bondi-Sachs rockets with nonzero cosmological constant. We
observe that the acceleration of the systems arises naturally in the asymptotic
symmetries of (anti-) de Sitter spacetimes. Assuming the validity of the
concepts of energy and mass previously introduced in asymptotically flat
spacetimes, we find that the emission of pure radiation energy balances the
loss of the Bondi mass in certain special families of the Bondi-Sachs rockets,
so in these there is no gravitational radiation.Comment: 12 pages, to appear in General Relativity and Gravitatio
Thermodynamical Metrics and Black Hole Phase Transitions
An important phase transition in black hole thermodynamics is associated with
the divergence of the specific heat with fixed charge and angular momenta, yet
one can demonstrate that neither Ruppeiner's entropy metric nor Weinhold's
energy metric reveals this phase transition. In this paper, we introduce a new
thermodynamical metric based on the Hessian matrix of several free energy. We
demonstrate, by studying various charged and rotating black holes, that the
divergence of the specific heat corresponds to the curvature singularity of
this new metric. We further investigate metrics on all thermodynamical
potentials generated by Legendre transformations and study correspondences
between curvature singularities and phase transition signals. We show in
general that for a system with n-pairs of intensive/extensive variables, all
thermodynamical potential metrics can be embedded into a flat (n,n)-dimensional
space. We also generalize the Ruppeiner metrics and they are all conformal to
the metrics constructed from the relevant thermodynamical potentials.Comment: Latex, 25 pages, reference added, typos corrected, English polished
and the Hawking-Page phase transition clarified; to appear in JHE
Hadronic Loop Corrections to the Muon Anomalous Magnetic Moment
The dominant theoretical uncertainties in both, the anomalous magnetic moment
of the muon and the value of the electromagnetic coupling at the Z scale arise
from their hadronic contributions. Since these will ultimately dominate the
experimental errors, we study the correlation between them, as well as with
other fundamental parameters. To this end we present analytical formulas for
the QCD contribution from higher energies and from heavy quarks. Including
these correlations affects the Higgs boson mass extracted from precision data.Comment: 4 page
Computational Analysis of the Spatiotemporal Coordination of Polarized PI3K and Rac1 Activities in Micro-Patterned Live Cells
Polarized molecular activities play important roles in guiding the cell toward persistent and directional migration. In this study, the polarized distributions of the activities of phosphatidylinositol 3-kinase (PI3K) and the Rac1 small GTPase were monitored using chimeric fluorescent proteins (FPs) in cells constrained on micro-patterned strips, with one end connecting to a neighboring cell (junction end) and the other end free of cell-cell contact (free end). The recorded spatiotemporal dynamics of the fluorescent intensity from different cells was scaled into a uniform coordinate system and applied to compute the molecular activity landscapes in space and time. The results revealed different polarization patterns of PI3K and Rac1 activity induced by the growth factor stimulation. The maximal intensity of different FPs, and the edge position and velocity at the free end were further quantified to analyze their correlation and decipher the underlying signaling sequence. The results suggest that the initiation of the edge extension occurred before the activation of PI3K, which led to a stable extension of the free end followed by the Rac1 activation. Therefore, the results support a concerted coordination of sequential signaling events and edge dynamics, underscoring the important roles played by PI3K activity at the free end in regulating the stable lamellipodia extension and cell migration. Meanwhile, the quantification methods and accompanying software developed can provide a convenient and powerful computational analysis platform for the study of spatiotemporal molecular distribution and hierarchy in live cells based on fluorescence images
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