4,080 research outputs found
Microfield Dynamics of Black Holes
The microcanonical treatment of black holes as opposed to the canonical
formulation is reviewed and some major differences are displayed. In particular
the decay rates are compared in the two different pictures.Comment: 22 pages, 4 figures, Revtex, Minor change in forma
Theoretical survey of tidal-charged black holes at the LHC
We analyse a family of brane-world black holes which solve the effective
four-dimensional Einstein equations for a wide range of parameters related to
the unknown bulk/brane physics. We first constrain the parameters using known
experimental bounds and, for the allowed cases, perform a numerical analysis of
their time evolution, which includes accretion through the Earth. The study is
aimed at predicting the typical behavior one can expect if such black holes
were produced at the LHC. Most notably, we find that, under no circumstances,
would the black holes reach the (hazardous) regime of Bondi accretion.
Nonetheless, the possibility remains that black holes live long enough to
escape from the accelerator (and even from the Earth's gravitational field) and
result in missing energy from the detectors.Comment: RevTeX4, 12 pages, 4 figures, 5 tables, minor changes to match the
accepted version in JHE
The bicycle-train travellers in the Netherlands: personal profiles and travel choices
The Netherlands seems to exhibit the unique conditions that allow cycling on the country level instead of only the city level. Moreover, the national transit system seemingly provides one crucial condition: citizens use the train and cycling systems in an integrated manner, with combined bicycle-train transport recently demonstrating strong growth. Relatively little is known about bicycle-train users, i.e. the people who combine the bicycle and the train in a single trip. In this paper, we investigate their profiles and travel choices, in terms of the modes they choose for access and egress travel, their choice of stations, and their choice of type of bicycles. Studying this specific group can add to our understanding of the role of the train system in the success of cycling in the Netherlands, in turn helping improve policy transfer to metropolitan areas in other countries. In 2017, in cooperation with the Dutch National Railways, researchers surveyed a sample of train travellers, ultimately resulting in more than 3000 completed questionnaires. Descriptive analyses revealed that, compared to train travellers who do not or rarely cycle to/from train stations, bicycle-train users are on average more likely to be young people who are engaged in full-time employment or entrepreneurs, commute to work and hold university degrees. As for their cycling behaviour, bicycle-train travellers use bicycles much more often on the home-end of train trips than on the activity-end. Furthermore, bicycle-train travellers infrequently use suburban stations on the home-end, preferring large stations in the centres of major cities instead. For those who use bicycles, shared bicycles claim a considerable share on the activity-end of a train trip
Ghost Busting: PT-Symmetric Interpretation of the Lee Model
The Lee model was introduced in the 1950s as an elementary quantum field
theory in which mass, wave function, and charge renormalization could be
carried out exactly. In early studies of this model it was found that there is
a critical value of g^2, the square of the renormalized coupling constant,
above which g_0^2, the square of the unrenormalized coupling constant, is
negative. Thus, for g^2 larger than this critical value, the Hamiltonian of the
Lee model becomes non-Hermitian. It was also discovered that in this
non-Hermitian regime a new state appears whose norm is negative. This state is
called a ghost state. It has always been assumed that in this ghost regime the
Lee model is an unacceptable quantum theory because unitarity appears to be
violated. However, in this regime while the Hamiltonian is not Hermitian, it
does possess PT symmetry. It has recently been discovered that a non-Hermitian
Hamiltonian having PT symmetry may define a quantum theory that is unitary. The
proof of unitarity requires the construction of a new time-independent operator
called C. In terms of C one can define a new inner product with respect to
which the norms of the states in the Hilbert space are positive. Furthermore,
it has been shown that time evolution in such a theory is unitary. In this
paper the C operator for the Lee model in the ghost regime is constructed
exactly in the V/N-theta sector. It is then shown that the ghost state has a
positive norm and that the Lee model is an acceptable unitary quantum field
theory for all values of g^2.Comment: 20 pages, 9 figure
A lower limit for Newtonian-noise models of the Einstein Telescope
The Einstein Telescope (ET) is a proposed third-generation gravitational-wave (GW) underground observatory. It will have greatly increased sensitivity compared to current GW detectors, and it is designed to extend the observation band down to a few Hz. At these frequencies, a major limitation of the ET sensitivity is predicted to be due to gravitational fluctuations produced by the environment, most importantly by the seismic field, which give rise to the so-called Newtonian noise (NN). Accurate models of ET NN are crucial to assess the compatibility of an ET candidate site with the ET sensitivity target also considering a possible reduction in NN by noise cancellation. With NN models becoming increasingly complex as they include details of geology and topography, it is crucial to have tools to make robust assessments of their accuracy. For this purpose, we derive a lower bound on seismic NN spectra, which is weakly dependent on geology and properties of the seismic field. As a first application, we use the lower limit to compare it with NN estimates recently calculated for the Sardinia and Euregio Meuse-Rhine (EMR) candidate sites. We find the utility of the method, which shows an inconsistency with the predictions for the EMR site, which indicates that ET NN models require further improvement
Black Hole Evaporation and Compact Extra Dimensions
We study the evaporation of black holes in space-times with extra dimensions
of size L. We first obtain a description which interpolates between the
expected behaviors of very large and very small black holes and then show that
the luminosity is greatly damped when the horizon shrinks towards L from a
larger value. Analogously, black holes born with an initial size smaller than L
are almost stable. This effect is due to the dependence of both the Hawking
temperature and the grey-body factor of a black hole on the dimensionality of
space. Although the picture of what happens when the horizon becomes of size L
is still incomplete, we argue that there occurs a (first order) phase
transition, possibly signaled by an outburst of energy which leaves a
quasi-stable remnant.Comment: RevTeX, 13 pages, 6 figures include
Malignant melanoma with osteosarcomatous differentiation in a lymph node metastasis
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145523/1/cup13283.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145523/2/cup13283_am.pd
Family Firm Configurations for High Performance: The Role of Entrepreneurship and Ambidexterity
The performance drivers of family firms have spawned considerable research interest. Almost exclusively this research has relied on independent sets of explanatory variables in linear analyses. These analyses mask the complex interdependencies that are likely to exist among key success factors, leading to faulty theory and misspecified implications for practice. As treatment, the authors propose a configuration approach to family firm performance that accounts for complex interdependencies among entrepreneurial, innovation and family influence conditions. Using a fuzzy set qualitative comparative analysis of a sample of 129 Finnish family firms, the authors identify sufficient conditions with regard to the existence or absence of antecedent conditions to family firm performance. These conditions include entrepreneurial orientation, exploration and exploitation activities that form causal paths towards family firm performance. To enrich the analysis, the authors theorize and empirically analyse how these conditions might differ in family firms with high and low levels of family influence. They deepen the current understanding of configurations that promote the performance of family firms, offer important implications for theory and practice, and set new directions for future research on the strategic management of family firms. The results are also virtually identical and insensitive to change across subjective and objective performance measures
Characterization of the seismic environment at the Sanford Underground Laboratory, South Dakota
An array of seismometers is being developed at the Sanford Underground
Laboratory, the former Homestake mine, in South Dakota to study the properties
of underground seismic fields and Newtonian noise, and to investigate the
possible advantages of constructing a third-generation gravitational-wave
detector underground. Seismic data were analyzed to characterize seismic noise
and disturbances. External databases were used to identify sources of seismic
waves: ocean-wave data to identify sources of oceanic microseisms, and surface
wind-speed data to investigate correlations with seismic motion as a function
of depth. In addition, sources of events contributing to the spectrum at higher
frequencies are characterized by studying the variation of event rates over the
course of a day. Long-term observations of spectral variations provide further
insight into the nature of seismic sources. Seismic spectra at three different
depths are compared, establishing the 4100-ft level as a world-class low
seismic-noise environment.Comment: 29 pages, 16 figure
Brane-world black holes and the scale of gravity
A particle in four dimensions should behave like a classical black hole if
the horizon radius is larger than the Compton wavelength or, equivalently, if
its degeneracy (measured by entropy in units of the Planck scale) is large. For
spherically symmetric black holes in 4 + d dimensions, both arguments again
lead to a mass threshold MC and degeneracy scale Mdeg of the order of the
fundamental scale of gravity MG. In the brane-world, deviations from the
Schwarzschild metric induced by bulk effects alter the horizon radius and
effective four-dimensional Euclidean action in such a way that MC \simeq Mdeg
might be either larger or smaller than MG. This opens up the possibility that
black holes exist with a mass smaller than MG and might be produced at the LHC
even if M>10 TeV, whereas effects due to bulk graviton exchanges remain
undetectable because suppressed by inverse powers of MG. Conversely, even if
black holes are not found at the LHC, it is still possible that MC>MG and MG
\simeq 1TeV.Comment: 4 pages, no figur
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