3,586 research outputs found

### Effects of dark energy on the efficiency of charged AdS black holes as heat engine

In this paper, we study the heat engine where charged AdS black holes
surrounded by dark energy is the working substance and the mechanical work is
done via $PdV$ term in the first law of black hole thermodynamics in the
extended phase space. We first investigate the effects of a kind of dark energy
(quintessence field in this paper) on the efficiency of the RN-AdS black holes
as heat engine defined as a rectangle closed path in the $P-V$ plane. We get
the exact efficiency formula and find that quintessence field can improve the
heat engine efficiency which will increase as the field density $\rho_q$ grows.
At some fixed parameters, we find that bigger volume difference between the
smaller black holes($V_1$) and the bigger black holes($V_2$ ) will lead to a
lower efficiency, while the bigger pressure difference $P_1-P_4$ will make the
efficiency higher but it is always smaller than 1 and will never be beyond
Carnot efficiency which is the maximum value of the efficiency constrained by
thermodynamics laws, this is consistent to the heat engine in traditional
thermodynamics. After making some special choices for thermodynamical
quantities, we find that the increase of electric charge $Q$ and normalization
factor $a$ can also promote heat engine efficiency which would infinitely
approach the Carnot limit when $Q$ or $a$ goes to infinity.Comment: 28 pages, 16 figures, refernces added, discussion and computation
improve

### Angular Momentum Independence of the Entropy Sum and Entropy Product for AdS Rotating Black Holes In All Dimensions

In this paper, we investigate the angular momentum independence of the
entropy sum and product for AdS rotating black holes based on the first law of
thermodynamics and a mathematical lemma related to Vandermonde determinant. The
advantage of this method is that the explicit forms of the spacetime metric,
black hole mass and charge are not needed but the Hawking temperature and
entropy formula on the horizons are necessary for static black holes, while our
calculations require the expressions of metric and angular velocity formula. We
find that the entropy sum is always independent of angular momentum for all
dimensions and the angular momentum-independence of entropy product only holds
for the dimensions $d>4$ with at least one rotation parameter $a_i=0$, while
the mass-free of entropy sum and entropy product for rotating black holes only
stand for higher dimensions ($d>4$) and for all dimensions, respectively. On
the other hand, we find that the introduction of a negative cosmological
constant does not affect the angular momentum-free of entropy sum and product
but the criterion for angular momentum-independence of entropy product will be
affected.Comment: 14 pages, 0 figures,accepted for publication in Physics Letters

### Single-Valued Hamiltonian via Legendre-Fenchel Transformation and Time Translation Symmetry

Under conventional Legendre transformation, systems with a non-convex
Lagrangian will result in a multi-valued Hamiltonian as a function of conjugate
momentum. This causes problems such as non-unitary time evolution of quantum
state and non-determined motion of classical particles, and is physically
unacceptable. In this work, we propose a new construction of single-valued
Hamiltonian by applying Legendre-Fenchel transformation, which is a
mathematically rigorous generalization of conventional Legendre transformation,
valid for non-convex Lagrangian systems, but not yet widely known to the
physics community. With the new single-valued Hamiltonian, we study spontaneous
breaking of time translation symmetry and derive its vacuum state. Applications
to theories of cosmology and gravitation are discussed.Comment: Journal Version, 16pp. All results + conclusions un-changed, only
minor refinements to clarify the importance of our new LFT method and its
physics applications; references adde

### Searching for $\Xi_{cc}^+$ in Relativistic Heavy Ion Collisions

We study the doubly charmed baryon $\Xi_{cc}^+$ in high energy nuclear
collisions. We solve the three-body Schroedinger equation with relativistic
correction and calculate the $\Xi_{cc}^+$ yield and transverse momentum
distribution via coalescence mechanism. For $\Xi_{cc}^+$ production in central
Pb+Pb collisions at LHC energy, the yield is extremely enhanced, and the
production cross section per binary collision is one order of magnitude larger
than that in p+p collisions. This indicates that, it is most probable to
discover $\Xi_{cc}^+$ in heavy ion collisions and its discovery can be
considered as a probe of the quark-luon plasma formation.Comment: 5 pages and 4 figure

### $\Omega_{ccc}$ Production in High Energy Nuclear Collisions

We investigate the production of $\Omega_{ccc}$ baryon in high energy nuclear
collisions via quark coalescence mechanism. The wave function of $\Omega_{ccc}$
is solved from the Schr\"odinger equation for the bound state of three charm
quarks by using the hyperspherical method. The production cross section of
$\Omega_{ccc}$ per binary collision in a central Pb+Pb collision at
$\sqrt{s_{NN}}=2.76$ TeV reaches 9 nb, which is at least two orders of
magnitude larger than that in a p+p collision at the same energy. Therefore, it
is most probable to discover $\Omega_{ccc}$ in heavy ion collisions at LHC, and
the observation will be a clear signature of the quark-gluon plasma formation.Comment: 6 pages, 5 figure

### Hard-gapped Holographic Superconductors

In this work we discuss the zero temperature limit of a "p-wave" holographic
superconductor. The bulk description consists of a non-Abelian SU(2) gauge
fields minimally coupled to gravity. We numerically construct the zero
temperature solution which is the gravity dual of the superconducting ground
state of the "p-wave" holographic superconductors. The solution is a smooth
soliton with zero horizon size and shows an emergent conformal symmetry in the
IR. We found the expected superconducting behavior. Using the near horizon
analysis we show that the system has a "hard gap" for the relevant gauge field
fluctuations. At zero temperature the real part of the conductivity is zero for
an excitation frequency less than the gap frequency. This is in contrast with
what has been observed in similar scalar- gravity-gauge systems (holographic
superconductors). We also discuss the low but finite temperature behavior of
our solution.Comment: 9 pages, latex, 6 figure

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