233 research outputs found
Hairy black holes in theories with massive gravitons
This is a brief survey of the known black hole solutions in the theories of
ghost-free bigravity and massive gravity. Various black holes exist in these
theories, in particular those supporting a massive graviton hair. However, it
seems that solutions which could be astrophysically relevant are the same as in
General Relativity, or very close to them. Therefore, the no-hair conjecture
essentially applies, and so it would be hard to detect the graviton mass by
observing black holes.Comment: References added. 20 pages, 3 figures, based on the talk given at the
7-th Aegean Summer School "Beyond Einstein's theory of gravity", September
201
The four fixed points of scale invariant single field cosmological models
We introduce a new set of flow parameters to describe the time dependence of
the equation of state and the speed of sound in single field cosmological
models. A scale invariant power spectrum is produced if these flow parameters
satisfy specific dynamical equations. We analyze the flow of these parameters
and find four types of fixed points that encompass all known single field
models. Moreover, near each fixed point we uncover new models where the scale
invariance of the power spectrum relies on having simultaneously time varying
speed of sound and equation of state. We describe several distinctive new
models and discuss constraints from strong coupling and superluminality.Comment: 24 pages, 6 figure
Монте-Карло моделирование фазового перехода адроны-КГП в столкновениях тяжелых ионов с помощью партонной модели
Quark gluon plasma (QGP) is a special state of nuclear matter where quarks and gluons behave like free particles. Recently, a number of investigations of this state with high temperature and/or density have been conducted using collisions of relativistic and ultra-relativistic heavy nuclei. It is accepted that depending on the temperature and density, 1st or the 2nd order phase transitions take place in hadron matter during the formation of QGP. Herein, we have modeled heavy ion collisions using a HIJING Monte-Carlo generator, taking into account the description of the 1st order phase transition as a probabilistic process. We analyzed the behavior of the fluctuations of the total (N = N+ – N–) and resultant (Q = N+ – N–) electric charges of the system. Different phases were introduced using the BDMPS (Baier – Dokshitzer – Mueller – Piegne – Schiff) model of parton energy loss during crossing through a dense nuclear medium.Кварк-глюонная плазма (КГП) является особым состоянием ядерной материи, при котором кварки и глюоны ведут себя как свободные частицы. В настоящее время проводятся исследования этого состояния вещества с высокими температурой и/или плотностью с помощью столкновений релятивистских и ультрарелятивистских тяжелых ядер. Считается, что адронная материя испытывает (в зависимости от температуры и плотности) фазовый переход первого или второго рода при образовании КГП. В данной статье были промоделированы столкновения тяжелых ионов с помощью Монте-Карло генератора HIJING с учетом описания фазового перехода первого рода как вероятностного процесса и проанализировано поведение флуктуаций полного (N = N+ – N–) и результирующего (Q = N+ – N–) электрических зарядов системы. Разные фазы были заданы с помощью BDMPS (Baier – Dokshitzer – Mueller – Piegne – Schiff) модели потери партонной энергии при прохождении через плотное ядерное вещество
Affine equation of state from quintessence and k-essence fields
We explore the possibility that a scalar field with appropriate Lagrangian
can mimic a perfect fluid with an affine barotropic equation of state. The
latter can be thought of as a generic cosmological dark component evolving as
an effective cosmological constant plus a generalized dark matter. As such, it
can be used as a simple, phenomenological model for either dark energy or
unified dark matter. Furthermore, it can approximate (up to first order in the
energy density) any barotropic dark fluid with arbitrary equation of state. We
find that two kinds of Lagrangian for the scalar field can reproduce the
desired behaviour: a quintessence-like with a hyperbolic potential, or a purely
kinetic k-essence one. We discuss the behaviour of these two classes of models
from the point of view of the cosmological background, and we give some hints
on their possible clustering properties.Comment: 9 pages, 6 figures. Minor updates, accepted by CQ
Quark-hadron phase transition with surface fluctuation
The effect of surface fluctuation on the observables of quark-hadron phase
transition is studied. The Ginzburg-Landau formalism is extended by the
inclusion of an extra term in the free energy that depends on the vertical
displacements from a flat surface. The probability that a bin has a particular
net displacement is determined by lattice simulation, where the physics input
is color confinement. The surface fluctuation from bin to bin is related to
multiplicity fluctuation, which in turn is measured by the factorial moments.
It is found that both the F-scaling behavior and the scaling exponent are
essentially unaffected by the inclusion of surface fluctuation.Comment: 9 pages, LaTex, 7 figures in a single postscript file, submitted to
Phys. Rev.
Possibility of cyclic Turnarounds In Brane-world Scenario: Phantom Energy Accretion onto Black Holes and its consequences
A universe described by braneworlds is studied in a cyclic scenario. As
expected such an oscillating universe will undergo turnarounds, whenever the
phantom energy density reaches a critical value from either side. It is found
that a universe described by RSII brane model will readily undergo oscillations
if, either the brane tension, \lambda, or the bulk cosmological constant,
\Lambda_{4}, is negative. The DGP brane model does not readily undergo cyclic
turnarounds. Hence for this model a modified equation is proposed to
incorporate the cyclic nature. It is found that there is always a remanent mass
of a black hole at the verge of a turnaround. Hence contrary to known results
in literature, it is found that the destruction of black holes at the
turnaround is completely out of question. Finally to alleviate, if not solve,
the problem posed by the black holes, it is argued that the remanent masses of
the black holes do not act as a serious defect of the model because of Hawking
evaporation.Comment: 10 pages, 2 figures; International Journal of Theoretical Physics
(2012
A high-fidelity noiseless amplifier for quantum light states
Noise is the price to pay when trying to clone or amplify arbitrary quantum
states. The quantum noise associated to linear phase-insensitive amplifiers can
only be avoided by relaxing the requirement of a deterministic operation. Here
we present the experimental realization of a probabilistic noiseless linear
amplifier that is able to amplify coherent states at the highest level of
effective gain and final state fidelity ever reached. Based on a sequence of
photon addition and subtraction, and characterized by a significant
amplification and low distortions, this high-fidelity amplification scheme may
become an essential tool for quantum communications and metrology, by enhancing
the discrimination between partially overlapping quantum states or by
recovering the information transmitted over lossy channels.Comment: 5 pages, 4 figure
The Self-Accelerating Universe with Vectors in Massive Gravity
We explore the possibility of realising self-accelerated expansion of the
Universe taking into account the vector components of a massive graviton. The
effective action in the decoupling limit contains an infinite number of terms,
once the vector degrees of freedom are included. These can be re-summed in
physically interesting situations, which result in non-polynomial couplings
between the scalar and vector modes. We show there are self-accelerating
background solutions for this effective action, with the possibility of having
a non-trivial profile for the vector fields. We then study fluctuations around
these solutions and show that there is always a ghost, if a background vector
field is present. When the background vector field is switched off, the ghost
can be avoided, at the price of entering into a strong coupling regime, in
which the vector fluctuations have vanishing kinetic terms. Finally we show
that the inclusion of a bare cosmological constant does not change the previous
conclusions and it does not lead to a ghost mode in the absence of a background
vector field.Comment: 23 pages, 2 figure
- …