25,155 research outputs found
Entropic force and its fluctuation in Euclidian quantum gravity
In this paper, we study the idea about gravity as entropic force proposed by
Verlinde. By applying the identification between partition functions of gravity
theory and the dual field theory, we find the gravitational force can be
calculated from the changing of entropy induced from its dual field theory
side. Unlike Verlinde's calculation, our method does not depend on other
assumptions such as equipartition of energy, so it is a safe check on the
entropic force idea. Also we show how entropic force can be derived by similar
method from gravity side along, which will provide a clue to a better
understanding on the gauge/gravity duality. At last, we study the fluctuation
of the force, and we find the fluctuation acting on the point-like particle can
never be larger than the expectation value of the force. For black hole in AdS
space, by gauge/gravity duality, the fluctuation is induced by thermal
fluctuation from field theory living on conformal boundary. And for the metric
of black hole in flat space, the ratio between fluctuation and force goes to a
constant at infinity. .Comment: typos revised, more detailed discussio
Naturalness from a Composite Top?
We consider a theory with composite top quarks but an elementary Higgs boson.
The hierarchy problem can be solved by supplementing TeV scale top
compositeness with either supersymmetry or Higgs compositeness appearing at the
multi-TeV scale. The Higgs boson couples to uncolored partons within the top
quark. We study how this approach can give rise to a novel screening effect
that suppresses production of the colored top partners at the LHC. Strong
constraints arise from Z to bb, as well potentially from flavor physics.
Independent of flavor considerations, current constraints imply a compositeness
scale near a TeV; this implies that the model is likely tuned at the percent
level. Four top quark production at the LHC is a smoking-gun probe of this
scenario. New CP violation in D meson mixing is also possible.Comment: Improved discussion of precision electroweak constraints. Expanded
discussion of potential mixing between composite and elementary fields.
Version to appear in JHE
Direct prediction of the solute softening-to-hardening transition in W-Re alloys using stochastic simulations of screw dislocation motion
Interactions among dislocations and solute atoms are the basis of several
important processes in metals plasticity. In body-centered cubic (bcc) metals
and alloys, low-temperature plastic flow is controlled by screw dislocation
glide, which is known to take place by the nucleation and sideward relaxation
of kink pairs across two consecutive \emph{Peierls} valleys. In alloys,
dislocations and solutes affect each other's kinetics via long-range stress
field coupling and short-range inelastic interactions. It is known that in
certain substitutional bcc alloys a transition from solute softening to solute
hardening is observed at a critical concentration. In this paper, we develop a
kinetic Monte Carlo model of screw dislocation glide and solute diffusion in
substitutional W-Re alloys. We find that dislocation kinetics is governed by
two competing mechanisms. At low solute concentrations, nucleation is enhanced
by the softening of the Peierls stress, which overcomes the elastic repulsion
of Re atoms on kinks. This trend is reversed at higher concentrations,
resulting in a minimum in the flow stress that is concentration and temperature
dependent. This minimum marks the transition from solute softening to
hardening, which is found to be in reasonable agreement with experiments
Dark Matter Induced Nucleon Decay: Model and Signatures
If dark matter (DM) carries anti-baryon number, a DM particle may annihilate
with a nucleon by flipping to anti-DM. Inspired by Hylogenesis models, we
introduce a single component DM model where DM is asymmetric and carries B and
L as -1/2. It can annihilate with a nucleon to an anti-lepton and an anti-DM at
leading order or with an additional meson at sub-leading order. Such signals
may be observed in proton decay experiments. If DM is captured in the Sun, the
DM induced nucleon decay can generate a large flux of anti-neutrinos, which
could be observed in neutrino experiments. Furthermore, the anti-DM particle in
the final state obtains a relatively large momentum (few hundred MeV), and
escapes the Sun. These fast-moving anti-DM particles could also induce
interesting signals in various underground experiments.Comment: Discussion about (g-2) is added. References are updated. Introduction
is expanded. Accepted by JHE
Algorithms for finding transposons in gene sequences
With the process of evolution, some genes will change their relative
positions in gene sequence. These "jumping genes" are called transposons.
Through some intuitive rules, we give a criterion to determine transposons
among gene sequences of different individuals of the same species. Then we turn
this problem into graph theory and give algorithms for different situations
with acceptable time complexities. One of these algorithms has been reported
briefly as the "iteration algorithm" in Kang et al.'s paper (in this paper,
transposon is called "core-gene-defined genome organizational framework",
cGOF). This paper provides the omitted details and discussions on general
cases.Comment: 5 pages, 2 figure
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