2,453 research outputs found
Impurity center in a semiconductor quantum ring in the presence of a radial electric field
The problem of an impurity electron in a quantum ring (QR) in the presence of
a radially directed strong external electric field is investigated in detail.
Both an analytical and a numerical approach to the problem are developed. The
analytical investigation focuses on the regime of a strong wire-electric field
compared to the electric field due to the impurity. An adiabatic and
quasiclassical approximation is employed. The explicit dependencies of the
binding energy of the impurity electron on the electric field strength,
parameters of the QR and position of the impurity within the QR are obtained.
Numerical calculations of the binding energy based on a finite-difference
method in two and three dimensions are performed for arbitrary strengths of the
electric field. It is shown that the binding energy of the impurity electron
exhibits a maximum as a function of the radial position of the impurity that
can be shifted arbitrarily by applying a corresponding wire-electric field. The
maximal binding energy monotonically increases with increasing electric field
strength. The inversion effect of the electric field is found to occur. An
increase of the longitudinal displacement of the impurity typically leads to a
decrease of the binding energy. Results for both low- and high-quantum rings
are derived and discussed. Suggestions for an experimentally accessible set-up
associated with the GaAs/GaAlAs QR are provided.Comment: 16 pages, 8 figure
One-photon decay of the tetraquark state in a relativistic constituent quark model with infrared confinement
We further explore the consequences of treating the X(3872) meson as a
tetraquark bound state by analyzing its one-photon decay X => \gamma + J/psi in
the framework of our approach developed in previous papers which incorporates
quark confinement in an effective way. To introduce electromagnetism we gauge a
nonlocal effective Lagrangian describing the interaction of the X(3872) meson
with its four constituent quarks by using the P-exponential path-independent
formalism. We calculate the matrix element of the transition X => \gamma+ J/psi
and prove its gauge invariance. We evaluate the X=> \gamma + J/psi decay width
and the longitudinal/transverse composition of the J/psi in this decay. For a
reasonable value of the size parameter of the X(3872) meson we find consistency
with the available experimental data. We also calculate the helicity and
multipole amplitudes of the process, and describe how they can be obtained from
the covariant transition amplitude by covariant projection.Comment: 13 pages, 5 figures. Typos corrected, version matching the one
published in PR
Observational constraints on early dark energy
We review and update constraints on the Early Dark Energy (EDE) model from
cosmological data sets, in particular Planck PR3 and PR4 cosmic microwave
background (CMB) data and large-scale structure (LSS) data sets including
galaxy clustering and weak lensing data from the Dark Energy Survey, Subaru
Hyper Suprime-Cam, and KiDS+VIKING-450, as well as BOSS/eBOSS galaxy clustering
and Lyman- forest data. We detail the fit to CMB data, and perform the
first analyses of EDE using the CAMSPEC and Hillipop likelihoods for Planck CMB
data, rather than Plik, both of which yield a tighter upper bound on the
allowed EDE fraction than that found with Plik. We then supplement CMB data
with large-scale structure data in a series of new analyses. All these analyses
are concordant in their Bayesian preference for CDM over EDE, as
indicated by marginalized posterior distributions. We perform a series of tests
of the impact of priors in these results, and compare with frequentist analyses
based on the profile likelihood, finding qualitative agreement with the
Bayesian results. All these tests suggest prior volume effects are not a
determining factor in analyses of EDE. This work provides both a review of
existing constraints and several new analyses.Comment: 59 pages, 23 figures, 11 tables, Invited review for International
Journal of Modern Physics
Constraining Early Dark Energy with Large-Scale Structure
An axion-like field comprising of the energy density of the
universe near matter-radiation equality is a candidate to resolve the Hubble
tension; this is the "early dark energy" (EDE) model. However, as shown in Hill
et al. (2020), the model fails to simultaneously resolve the Hubble tension and
maintain a good fit to both cosmic microwave background (CMB) and large-scale
structure (LSS) data. Here, we use redshift-space galaxy clustering data to
sharpen constraints on the EDE model. We perform the first EDE analysis using
the full-shape power spectrum likelihood from the Baryon Oscillation
Spectroscopic Survey (BOSS), based on the effective field theory (EFT) of LSS.
The inclusion of this likelihood in the EDE analysis yields a tighter
error bar on compared to primary CMB data alone, yielding km/s/Mpc ( CL). In addition, we constrain the
maximum fractional energy density contribution of the EDE to ( CL). We explicitly demonstrate that the EFT BOSS likelihood
yields much stronger constraints on EDE than the standard BOSS likelihood.
Including further information from photometric LSS surveys,the constraints
narrow by an additional , yielding km/s/Mpc
( CL) and ( CL). These bounds are obtained
without including local-universe data, which is in strong tension with
the CMB and LSS, even in the EDE model. We also refute claims that MCMC
analyses of EDE that omit SH0ES from the combined dataset yield misleading
posteriors. Finally, we demonstrate that upcoming Euclid/DESI-like
spectroscopic galaxy surveys can greatly improve the EDE constraints. We
conclude that current data preclude the EDE model as a resolution of the Hubble
tension, and that future LSS surveys can close the remaining parameter space of
this model.Comment: 26 pages, 12 figures. v2: Version to appear in Phys Rev D. Appendices
B and C demonstrate that EDE provides a worse fit than LCDM to Planck+BOSS
data, and that constraints are not driven by prior volume effect
Integrating out the heaviest quark in N--flavour ChPT
We extend a known method to integrate out the strange quark in three flavour
chiral perturbation theory to the context of an arbitrary number of flavours.
As an application, we present the explicit formulae to one--loop accuracy for
the heavy quark mass dependency of the low energy constants after decreasing
the number of flavours by one while integrating out the heaviest quark in
N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ
Exclusive semileptonic and nonleptonic decays of the Bc meson
We study exclusive nonleptonic and semileptonic decays of the Bc-meson within
a relativistic constituent quark model previously developed by us. For the
nonleptonic decays we use the factorizing approximation. We update our model
parameters by using new experimental data for the mass and the lifetime of the
Bc meson and the leptonic decay constants of the D-meson. We calculate the
branching ratios for a large set of exclusive nonleptonic and semileptonic
decays of the meson and compare our results with the results of other
studies. As a guide for further experimental exploration we provide explicit
formulas for the full angular decay distributions in the cascade decays Bc^- =>
J/psi(=> l^+l^-) + rho^-(=> pi^- pi^0) and Bc^- => J/psi(=> l^+l^-) +
W^-(off-shell)(=> l^- + nubar).Comment: 19 pages, 2 figure
Nonlinear supersymmetry: from classical to quantum mechanics
Quantization of the nonlinear supersymmetry faces a problem of a quantum
anomaly. For some classes of superpotentials, the integrals of motion admit the
corrections guaranteeing the preservation of the nonlinear supersymmetry at the
quantum level. With an example of the system realizing the nonlinear
superconformal symmetry, we discuss the nature of such corrections and
speculate on their possible general origin.Comment: 11 page
Ultra-light axions and the tension: joint constraints from the cosmic microwave background and galaxy clustering
We search for ultra-light axions as dark matter (DM) and dark energy particle
candidates, for axion masses , by a joint analysis of cosmic microwave background
(CMB) and galaxy clustering data -- and consider if axions can resolve the
tension in inferred values of the matter clustering parameter . We give
legacy constraints from Planck 2018 CMB data, improving 2015 limits on the
axion density by up to a factor of three; CMB data from
the Atacama Cosmology Telescope and the South Pole Telescope marginally weaken
Planck bounds at , owing to lower (and
theoretically-consistent) gravitational lensing signals. We jointly infer, from
Planck CMB and full-shape galaxy power spectrum and bispectrum data from the
Baryon Oscillation Spectroscopic Survey (BOSS), that axions are, today, of the DM for and for
. BOSS data
strengthen limits, in particular at higher by probing
high-wavenumber modes (). BOSS alone finds a
preference for axions at , for , but Planck disfavours this result. Nonetheless, axions
in a window can improve consistency between CMB and galaxy
clustering data, e.g., reducing the discrepancy from to , since these axions suppress structure growth at the scales to which is sensitive. We expect improved
constraints with upcoming high-resolution CMB and galaxy lensing and future
galaxy clustering data, where we will further assess if axions can restore
cosmic concordance.Comment: 52 pages, 22 figure
Superconformal mechanics and nonlinear supersymmetry
We show that a simple change of the classical boson-fermion coupling
constant, , , in the superconformal mechanics
model gives rise to a radical change of a symmetry: the modified classical and
quantum systems are characterized by the nonlinear superconformal symmetry. It
is generated by the four bosonic integrals which form the so(1,2) x u(1)
subalgebra, and by the 2(n+1) fermionic integrals constituting the two spin-n/2
so(1,2)-representations and anticommuting for the order n polynomials of the
even generators. We find that the modified quantum system with an integer value
of the parameter is described simultaneously by the two nonlinear
superconformal symmetries of the orders relatively shifted in odd number. For
the original quantum model with , , this means the
presence of the order 2p nonlinear superconformal symmetry in addition to the
osp(2|2) supersymmetry.Comment: 16 pages; misprints corrected, note and ref added, to appear in JHE
Higher Spins from Tensorial Charges and OSp(N|2n) Symmetry
It is shown that the quantization of a superparticle propagating in an N=1,
D=4 superspace extended with tensorial coordinates results in an infinite tower
of massless spin states satisfying the Vasiliev unfolded equations for free
higher spin fields in flat and AdS_4 N=1 superspace. The tensorial extension of
the AdS_4 superspace is proved to be a supergroup manifold OSp(1|4). The model
is manifestly invariant under an OSp(N|8) (N=1,2) superconformal symmetry. As a
byproduct, we find that the Cartan forms of arbitrary Sp(2n) and OSp(1|2n)
groups are GL(2n) flat, i.e. they are equivalent to flat Cartan forms up to a
GL(2n) rotation. This property is crucial for carrying out the quantization of
the particle model on OSp(1|4) and getting the higher spin field dynamics in
super AdS_4, which can be performed in a way analogous to the flat case.Comment: LaTeX, 21 page (JHEP style), misprints corrected, added comments on
the relation of results of hep-th/0106149 with hep-th/9904109 and
hep-th/9907113, references adde
- …