1,002 research outputs found
Eikonal equation of the Lorentz-violating Maxwell theory
We derive the eikonal equation of light wavefront in the presence of Lorentz
invariance violation (LIV) from the photon sector of the standard model
extension (SME). The results obtained from the equations of and
fields respectively are the same. This guarantees the
self-consistency of our derivation. We adopt a simple case with only one
non-zero LIV parameter as an illustration, from which we find two points. One
is that, in analogy with Hamilton-Jacobi equation, from the eikonal equation,
we can derive dispersion relations which are compatible with results obtained
from other approaches. The other is that, the wavefront velocity is the same as
the group velocity, as well as the energy flow velocity. If further we define
the signal velocity as the front velocity, there always exists a mode
with , hence causality is violated classically. Thus our method might be
useful in the analysis of Lorentz violation in QED in terms of classical
causality .Comment: 14 latex pages, no figure, final version for publication in EPJ
Lorentz violation from cosmological objects with very high energy photon emissions
Lorentz violation (LV) is predicted by some quantum gravity theories, where
photon dispersion relation is modified, and the speed of light becomes
energy-dependent. Consequently, it results in a tiny time delay between high
energy photons and low energy ones. Very high energy (VHE) photon emissions
from cosmological distance can amplify these tiny LV effects into observable
quantities. Here we analyze four VHE -ray bursts (GRBs) from Fermi
observations, and briefly review the constraints from three TeV flares of
active galactic nuclei (AGNs) as well. One step further, we present a first
robust analysis of VHE GRBs taking the intrinsic time lag caused by sources
into account, and give an estimate to quantum gravity energy GeV for linear energy dependence, and GeV for
quadratic dependence. However, the statistics is not sufficient due to the lack
of data, and further observational results are desired to constrain LV effects
better.Comment: 14 pages, 2 figures, final version to appear in Astroparticle Physic
Van der Waals-like phase transition from holographic entanglement entropy in Lorentz breaking massive gravity
In this paper, phase transition of AdS black holes in lorentz breaking
massive gravity has been studied in the framework of holography. We find that
there is a first order phase transition(FPT) and second order phase
transition(SPT) both in Bekenstein-Hawking entropy(BHE)-temperature plane and
holographic entanglement entropy(HEE)-temperature plane. Furthermore, for the
FPT, the equal area law is checked and for the SPT, the critical exponent of
the heat capacity is also computed. Our results confirm that the phase
structure of HEE is similar to that of BHE in lorentz breaking massive gravity,
which implies that HEE and BHE have some potential underlying relationship.Comment: 10 pages, 10 figure
Mutual correlation in the shock wave geometry
We probe the shock wave geometry with the mutual correlation in a spherically
symmetric Reissner Nordstr\"om AdS black hole on the basis of the gauge/gravity
duality. In the static background, we find that the regions living on the
boundary of the AdS black holes are correlated provided the considered regions
on the boundary are large enough. We also investigate the effect of the charge
on the mutual correlation and find that the bigger the value of the charge is,
the smaller the value of the mutual correlation will to be. As a small
perturbation is added at the AdS boundary, the horizon shifts and a dynamical
shock wave geometry forms after long time enough. In this dynamic background,
we find that the greater the shift of the horizon is, the smaller the mutual
correlation will to be. Especially for the case that the shift is large enough,
the mutual correlation vanishes, which implies that the considered regions on
the boundary are uncorrelated. The effect of the charge on the mutual
correlation in this dynamic background is found to be the same as that in the
static background.Comment: 10 page
Comment on "Optimal convex approximations of quantum states"
In a recent paper, M. F. Sacchi [Phys. Rev. A 96, 042325 (2017)] addressed
the general problem of approximating an unavailable quantum state by the convex
mixing of different available states. For the case of qubit mixed states, we
show that the analytical solutions in some cases are invalid. In this Comment,
we present complete analytical solutions for the optimal convex approximation.
Our solutions can be viewed as correcting and supplementing the results in the
aforementioned paper.Comment: 4 pages, 2 figure
Complete characterization of qubit masking
We study the problem of information masking through nonzero linear operators
that distribute information encoded in single qubits to the correlations
between two qubits. It is shown that a nonzero linear operator cannot mask any
nonzero measure set of qubit states. We prove that the maximal maskable set of
states on the Bloch sphere with respect to any masker is the ones on a
spherical circle. Any states on a spherical circle on the Bloch sphere are
maskable, which also proves the conjecture on maskable qubit states given by
Modi et al. [Phys. Rev. Lett. 120, 230501 (2018)]. we provide explicitly
operational unitary maskers for all maskable sets. As applications, different
protocols for secret sharing are introduced.Comment: 6 pages, 3 figure
Deterministic versus probabilistic quantum information masking
We investigate quantum information masking for arbitrary dimensional quantum
states. We show that mutually orthogonal quantum states can always be served
for deterministic masking of quantum information. We further construct a
probabilistic masking machine for linearly independent states. It is shown that
a set of d dimensional states, , , can be probabilistically masked by a general
unitary-reduction operation if they are linearly independent. The maximal
successful probability of probabilistic masking is analyzed and derived for the
case of two initial states.Comment: 5 pages, 1 figure
Impossibility of masking a set of quantum states of nonzero measure
We study the quantum information masking based on isometric linear operators
that distribute the information encoded in pure states to the correlations in
bipartite states. It is shown that a isometric linear operator can not mask any
nonzero measure set of pure states. We present a geometric characterization of
the maskable sets, and show that any maskable set must be on a spherical circle
in certain Euclidean spaces. Detailed examples and potential applications in
such as secret sharing and quantum cryptography are analyzed.Comment: 7 pages, 3 figures, comments are welcome
Photon Gas Thermodynamics in Doubly Special Relativity
Doubly special relativity (DSR), with both an invariant velocity and an
invariant length scale, elegantly preserves the principle of relativity between
moving observers, and appears as a promising candidate of the quantum theory of
gravity. We study the modifications of photon gas thermodynamics in the
framework of DSR with an invariant length , after properly taking
into account the effects of modified dispersion relation, upper bounded
energy-momentum space, and deformed integration measure. We show that with a
positive , the grand partition function, the energy density, the
specific heat, the entropy, and the pressure are smaller than those of special
relativity (SR), while the velocity of photons and the ratio of pressure to
energy are larger. In contrast, with a negative , the quantum gravity
effects show up in the opposite direction. However, these effects only manifest
themselves significantly when the temperature is larger than . Thus, DSR can have considerable influence on the early universe in
cosmological study.Comment: 17 pages, 7 figures, final version for publication in AP
Icosahedral B\u3csub\u3e12\u3c/sub\u3e-containing core–shell structures of B\u3csub\u3e80\u3c/sub\u3e
Low-lying icosahedral (Ih) B12-containing structures of B80 are explored, and a number of core–shell isomers are found to have lower energy than the previous predicted B80 fullerene. The structural transformation of boron clusters from tubular structure to core–shell structure may occur at a critical size less than B80
- …