71,054 research outputs found

### Nonlinear realisation approach to topologically massive supergravity

We develop a nonlinear realisation approach to topologically massive
supergravity in three dimensions, with and without a cosmological term. It is a
natural generalisation of a similar construction for ${\cal N}=1$ supergravity
in four dimensions, which was recently proposed by one of us. At the heart of
both formulations is the nonlinear realisation approach to gravity which was
given by Volkov and Soroka fifty years ago in the context of spontaneously
broken local supersymmetry. In our setting, the action for cosmological
topologically massive supergravity is invariant under two different local
supersymmetries. One of them acts on the Goldstino, while the other
supersymmetry leaves the Goldstino invariant. The former can be used to gauge
away the Goldstino, and then the resulting action coincides with that given in
the literature.Comment: 29 page

### The passage of time and top-down causation

It is often claimed that the fundamental laws of physics are deterministic
and time-symmetric and that therefore our experience of the passage of time is
an illusion. This paper will critically discuss these claims and show that they
are based on the misconception that the laws of physics are an exact and
complete description of nature. I will argue that all supposedly fundamental
deterministic and time-symmetric laws have their limitations and are
supplemented by stochastic and irreversible elements. In fact, a deterministic
description of a system is valid only as long as interactions with the rest of
the world can be ignored. The most famous example is the quantum measurement
process that occurs when a quantum system interacts with a macroscopic
environment such as a measurement apparatus. This environment determines in a
top-down way the possible outcomes of the measurement and their probabilities.
I will argue that more generally the possible events that can occur in a system
and their probabilities are the result of top-down influences from the wider
context. In this way the microscopic level of a system is causally open to
influences from the macroscopic environment. In conclusion, indeterminism and
irreversibility are the result of a system being embedded in a wider context.Comment: This paper is based on a talk given at the MG16 conference in July
2021, and it appeared this year in the proceedings of this conference
(online, open access, and print

### Time dilation of quantum clocks in a Newtonian gravitational field

We consider two non-relativistic quantum clocks interacting with a Newtonian
gravitational field produced by a spherical mass. In the framework of Page and
Wootters approach, we derive a time dilation for the time states of the clocks.
The delay is in agreement up to first order with the gravitational time
dilation obtained from the Schwarzschild metric. This result can be extended by
considering the relativistic gravitational potential: in this case we obtain
the agreement with the exact Schwarzschild solution.Comment: 11 pages, 3 figure

### Quantum Mechanics Lecture Notes. Selected Chapters

These are extended lecture notes of the quantum mechanics course which I am
teaching in the Weizmann Institute of Science graduate physics program. They
cover the topics listed below. The first four chapter are posted here. Their
content is detailed on the next page. The other chapters are planned to be
added in the coming months.
1. Motion in External Electromagnetic Field. Gauge Fields in Quantum
Mechanics.
2. Quantum Mechanics of Electromagnetic Field
3. Photon-Matter Interactions
4. Quantization of the Schr\"odinger Field (The Second Quantization)
5. Open Systems. Density Matrix
6. Adiabatic Theory. The Berry Phase. The Born-Oppenheimer Approximation
7. Mean Field Approaches for Many Body Systems -- Fermions and Boson

### Soliton Gas: Theory, Numerics and Experiments

The concept of soliton gas was introduced in 1971 by V. Zakharov as an
infinite collection of weakly interacting solitons in the framework of
Korteweg-de Vries (KdV) equation. In this theoretical construction of a diluted
soliton gas, solitons with random parameters are almost non-overlapping. More
recently, the concept has been extended to dense gases in which solitons
strongly and continuously interact. The notion of soliton gas is inherently
associated with integrable wave systems described by nonlinear partial
differential equations like the KdV equation or the one-dimensional nonlinear
Schr\"odinger equation that can be solved using the inverse scattering
transform. Over the last few years, the field of soliton gases has received a
rapidly growing interest from both the theoretical and experimental points of
view. In particular, it has been realized that the soliton gas dynamics
underlies some fundamental nonlinear wave phenomena such as spontaneous
modulation instability and the formation of rogue waves. The recently
discovered deep connections of soliton gas theory with generalized
hydrodynamics have broadened the field and opened new fundamental questions
related to the soliton gas statistics and thermodynamics. We review the main
recent theoretical and experimental results in the field of soliton gas. The
key conceptual tools of the field, such as the inverse scattering transform,
the thermodynamic limit of finite-gap potentials and the Generalized Gibbs
Ensembles are introduced and various open questions and future challenges are
discussed.Comment: 35 pages, 8 figure

### A decoherence-based approach to the classical limit in Bohm's theory

The paper explains why the de Broglie-Bohm theory reduces to Newtonian mechanics in the macroscopic classical limit. The quantum-to-classical transition is based on three steps: (i) interaction with the environment produces effectively factorized states, leading to the formation of effective wave functions and hence decoherence; (ii) the effective wave functions selected by the environmentâ€“the pointer states of decoherence theoryâ€“will be well-localized wave packets, typically Gaussian states; (iii) the quantum potential of a Gaussian state becomes negligible under standard classicality conditions; therefore, the effective wave function will move according to Newtonian mechanics in the correct classical limit. As a result, a Bohmian system in interaction with the environment will be described by an effective Gaussian state andâ€“when the system is macroscopicâ€“it will move according to Newtonian mechanics

### Noether's second theorem and covariant field theory of mechanical stresses in inhomogeneous ionic liquids

In this paper, we present a covariant approach that utilizes Noether's second
theorem to derive a symmetric stress tensor from the grand thermodynamic
potential functional. We focus on the practical case where the density of the
grand thermodynamic potential is dependent on the first and second coordinate
derivatives of the scalar order parameters. Our approach is applied to several
models of inhomogeneous ionic liquids that consider electrostatic correlations
of ions or short-range correlations related to packing effects. Specifically,
we derive analytical expressions for the symmetric stress tensors of the
Cahn-Hilliard-like model, Bazant-Storey-Kornyshev model, and
Maggs-Podgornik-Blossey model. All of these expressions are found to be
consistent with respective self-consistent field equations.Comment: Submitted to Journal of Chemical Physic

### Worldtube excision method for intermediate-mass-ratio inspirals: scalar-field model in 3+1 dimensions

Binary black hole simulations become increasingly more computationally
expensive with smaller mass ratios, partly because of the longer evolution
time, and partly because the lengthscale disparity dictates smaller time steps.
The program initiated by Dhesi et al. (arXiv:2109.03531) explores a method for
alleviating the scale disparity in simulations with mass ratios in the
intermediate astrophysical range ($10^{-4} \lesssim q \lesssim 10^{-2}$), where
purely perturbative methods may not be adequate. A region ("worldtube") much
larger than the small black hole is excised from the numerical domain, and
replaced with an analytical model approximating a tidally deformed black hole.
Here we apply this idea to a toy model of a scalar charge in a fixed circular
geodesic orbit around a Schwarzschild black hole, solving for the massless
Klein-Gordon field. This is a first implementation of the worldtube excision
method in full 3+1 dimensions. We demonstrate the accuracy and efficiency of
the method, and discuss the steps towards applying it for evolving orbits and,
ultimately, in the binary black-hole scenario. Our implementation is publicly
accessible in the SpECTRE numerical relativity code.Comment: 19 pages, 10 figure

### On the fermionic couplings of axionic dark matter

In the non-relativistic limit, two types of dark matter axion interactions
with fermions are thought to dominate: one is induced by the spatial gradient
of the axion field and called the axion wind, and the other by the
time-derivative of the axion field, generating axioelectric effects. By
generalizing Schiff theorem, it is demonstrated that this latter operator is
actually strongly screened. For a neutral fermion, it can be entirely rotated
away and is unobservable. For charged fermions, the only effect that can peek
through the screening is an axion-induced electric dipole moment (EDM). These
EDMs are not related to the axion coupling to gluons, represent a prediction of
the Dirac theory analogous to the g = 2 magnetic moments, are not further
screened by the original Schiff theorem, and are ultimately responsible for
inducing the usual axioelectric ionization. The two main phenomenological
consequences are then that first the axion-induced neutron EDM could be several
orders of magnitude larger than expected from the axion gluonic coupling, and
second, that the electron EDM could also become available, and could actually
be highly sensitive to relic axions.Comment: 30 pages, no figure. Status of the axioelectric effect clarified, and
improved EDM numerical estimate

### Model-Independent Determination of $H_0$ and $\Omega_{K,0}$ using Time-Delay Galaxy Lenses and Gamma-Ray Bursts

Combining the `time-delay distance' ($D_{\Delta t}$) measurements from galaxy
lenses and other distance indicators provides model-independent determinations
of the Hubble constant ($H_0$) and spatial curvature ($\Omega_{K,0}$), only
based on the validity of the Friedmann-Lema\^itre-Robertson-Walker (FLRW)
metric and geometrical optics. To take the full merit of combining $D_{\Delta
t}$ measurements in constraining $H_0$, we use gamma-ray burst (GRB) distances
to extend the redshift coverage of lensing systems much higher than that of
Type Ia Supernovae (SNe Ia) and even higher than quasars, whilst the general
cosmography with a curvature component is implemented for the GRB distance
parametrizations. Combining Lensing+GRB yields $H_0=71.5^{+4.4}_{-3.0}$~km
s$^{-1}$Mpc$^{-1}$ and $\Omega_{K,0} = -0.07^{+0.13}_{-0.06}$ (1$\sigma$). A
flat-universe prior gives slightly an improved $H_0 = 70.9^{+4.2}_{-2.9}$~km
s$^{-1}$Mpc$^{-1}$. When combining Lensing+GRB+SN Ia, the error bar $\Delta
H_0$ falls by 25\%, whereas $\Omega_{K,0}$ is not improved due to the
degeneracy between SN Ia absolute magnitude, $M_B$, and $H_0$ along with the
mismatch between the SN Ia and GRB Hubble diagrams at $z\gtrsim 1.4$. Future
increment of GRB observations can help to moderately eliminate the $M_B-H_0$
degeneracy in SN Ia distances and ameliorate the restrictions on cosmographic
parameters along with $\Omega_{K,0}$ when combining Lensing+SN Ia+GRB. We
conclude that there is no evidence of significant deviation from a (an) flat
(accelerating) universe and $H_0$ is currently determined at 3\% precision. The
measurements show great potential to arbitrate the $H_0$ tension between the
local distance ladder and cosmic microwave background measurements and provide
a relevant consistency test of the FLRW metric.Comment: Accepted for publication in MNRA

- â€¦