5,393 research outputs found
What is the probability that a random integral quadratic form in variables has an integral zero?
We show that the density of quadratic forms in variables over that are isotropic is a rational function of , where the rational
function is independent of , and we determine this rational function
explicitly. When real quadratic forms in variables are distributed
according to the Gaussian Orthogonal Ensemble (GOE) of random matrix theory, we
determine explicitly the probability that a random such real quadratic form is
isotropic (i.e., indefinite).
As a consequence, for each , we determine an exact expression for the
probability that a random integral quadratic form in variables is isotropic
(i.e., has a nontrivial zero over ), when these integral quadratic
forms are chosen according to the GOE distribution. In particular, we find an
exact expression for the probability that a random integral quaternary
quadratic form has an integral zero; numerically, this probability is
approximately .Comment: 17 pages. This article supercedes arXiv:1311.554
Freezing Transition, Characteristic Polynomials of Random Matrices, and the Riemann Zeta-Function
We argue that the freezing transition scenario, previously explored in the
statistical mechanics of 1/f-noise random energy models, also determines the
value distribution of the maximum of the modulus of the characteristic
polynomials of large N x N random unitary (CUE) matrices. We postulate that our
results extend to the extreme values taken by the Riemann zeta-function zeta(s)
over sections of the critical line s=1/2+it of constant length and present the
results of numerical computations in support. Our main purpose is to draw
attention to possible connections between the statistical mechanics of random
energy landscapes, random matrix theory, and the theory of the Riemann zeta
function.Comment: published version with a few misprints corrected and references adde
Search for Electromagnetic Counterparts to LIGO-Virgo Candidates: Expanded Very Large Array
This paper summarizes a search for radio wavelength counterparts to candidate
gravitational wave events. The identification of an electromagnetic counterpart
could provide a more complete understanding of a gravitational wave event,
including such characteristics as the location and the nature of the
progenitor. We used the Expanded Very Large Array (EVLA) to search six galaxies
which were identified as potential hosts for two candidate gravitational wave
events. We summarize our procedures and discuss preliminary results.Comment: 4 pages; to appear in the New Horizons in Time Domain Astronomy,
Proceedings of IAU Symposium 285, eds. R. E. M. Griffin, R. J. Hanisch & R.
Seama
Liver transplant recipients’ experiences and perspectives of a telehealth-delivered lifestyle programme A qualitative study
Introduction Dietary modification and exercise are encouraged to address cardiometabolic risk factors after solid organ transplantation. However, the lived experience of attempting positive lifestyle changes for liver transplant recipients is not known. The aim of this study was to explore the experiences of liver transplant recipients and their perspectives of a 12-week telehealth lifestyle programme and assess the feasibility of this innovative health service. Methods Focus groups and one-on-one interviews were conducted with participants who had completed a 12-week, group-based, telehealth-delivered diet and exercise programme and thematic qualitative analysis was used to code and theme the data. Results In total, 19 liver transplant recipients participated in the study (25-68 years, median time since transplant 4.4 years, 63% male). Overarching themes included: (a) 'broad telehealth advantages' which highlighted that telehealth reduced the perceived burdens of face-to-face care; (b) 'impact of employment' which identified employment as a competing priority and appeared to effect involvement with the programme; (c) 'adapting Mediterranean eating pattern to meet individual needs' which identified the adaptability of the Mediterranean diet supported by sessions with the dietitian; (d) 'increasing exercise confidence' which recognised that a tailored approach facilitated confidence and acceptability of the exercise component of the programme. Discussion A telehealth lifestyle programme delivered by dietitians and exercise physiologists is an acceptable alternative to face-to-face care that can meet the needs of liver transplant recipients. There is a need to further innovate and broaden the scope of routine service delivery beyond face-to-face consultations
A new correlator in quantum spin chains
We propose a new correlator in one-dimensional quantum spin chains, the
Emptiness Formation Probability (EFP). This is a natural generalization
of the Emptiness Formation Probability (EFP), which is the probability that the
first spins of the chain are all aligned downwards. In the EFP we let
the spins in question be separated by sites. The usual EFP corresponds to
the special case when , and taking allows us to quantify non-local
correlations. We express the EFP for the anisotropic XY model in a
transverse magnetic field, a system with both critical and non-critical
regimes, in terms of a Toeplitz determinant. For the isotropic XY model we find
that the magnetic field induces an interesting length scale.Comment: 6 pages, 1 figur
Random matrix theory, the exceptional Lie groups, and L-functions
There has recently been interest in relating properties of matrices drawn at
random from the classical compact groups to statistical characteristics of
number-theoretical L-functions. One example is the relationship conjectured to
hold between the value distributions of the characteristic polynomials of such
matrices and value distributions within families of L-functions. These
connections are here extended to non-classical groups. We focus on an explicit
example: the exceptional Lie group G_2. The value distributions for
characteristic polynomials associated with the 7- and 14-dimensional
representations of G_2, defined with respect to the uniform invariant (Haar)
measure, are calculated using two of the Macdonald constant term identities. A
one parameter family of L-functions over a finite field is described whose
value distribution in the limit as the size of the finite field grows is
related to that of the characteristic polynomials associated with the
7-dimensional representation of G_2. The random matrix calculations extend to
all exceptional Lie groupsComment: 14 page
Signatures of homoclinic motion in quantum chaos
Homoclinic motion plays a key role in the organization of classical chaos in
Hamiltonian systems. In this Letter, we show that it also imprints a clear
signature in the corresponding quantum spectra. By numerically studying the
fluctuations of the widths of wavefunctions localized along periodic orbits we
reveal the existence of an oscillatory behavior, that is explained solely in
terms of the primary homoclinic motion. Furthermore, our results indicate that
it survives the semiclassical limit.Comment: 5 pages, 4 figure
Characteristic Polynomials of Sample Covariance Matrices: The Non-Square Case
We consider the sample covariance matrices of large data matrices which have
i.i.d. complex matrix entries and which are non-square in the sense that the
difference between the number of rows and the number of columns tends to
infinity. We show that the second-order correlation function of the
characteristic polynomial of the sample covariance matrix is asymptotically
given by the sine kernel in the bulk of the spectrum and by the Airy kernel at
the edge of the spectrum. Similar results are given for real sample covariance
matrices
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