233 research outputs found
On the Atomic Photoeffect in Non-relativistic QED
In this paper we present a mathematical analysis of the photoelectric effect
for one-electron atoms in the framework of non-relativistic QED. We treat
photo-ionization as a scattering process where in the remote past an atom in
its ground state is targeted by one or several photons, while in the distant
future the atom is ionized and the electron escapes to spacial infinity. Our
main result shows that the ionization probability, to leading order in the
fine-structure constant, , is correctly given by formal time-dependent
perturbation theory, and, moreover, that the dipole approximation produces an
error of only sub-leading order in . In this sense, the dipole
approximation is rigorously justified.Comment: 25 page
Ground States in the Spin Boson Model
We prove that the Hamiltonian of the model describing a spin which is
linearly coupled to a field of relativistic and massless bosons, also known as
the spin-boson model, admits a ground state for small values of the coupling
constant lambda. We show that the ground state energy is an analytic function
of lambda and that the corresponding ground state can also be chosen to be an
analytic function of lambda. No infrared regularization is imposed. Our proof
is based on a modified version of the BFS operator theoretic renormalization
analysis. Moreover, using a positivity argument we prove that the ground state
of the spin-boson model is unique. We show that the expansion coefficients of
the ground state and the ground state energy can be calculated using regular
analytic perturbation theory
Binding threshold for the Pauli-Fierz operator
For the Pauli-Fierz operator with a short range potential we study the
binding threshold as a function of the fine structure constant and
show that it converges to the binding threshold for the Schr\"odinger operator
in the small limit
Absence of Ground States for a Class of Translation Invariant Models of Non-relativistic QED
We consider a class of translation invariant models of non-relativistic QED
with net charge. Under certain natural assumptions we prove that ground states
do not exist in the Fock space
Towards a construction of inclusive collision cross-sections in the massless Nelson model
The conventional approach to the infrared problem in perturbative quantum
electrodynamics relies on the concept of inclusive collision cross-sections. A
non-perturbative variant of this notion was introduced in algebraic quantum
field theory. Relying on these insights, we take first steps towards a
non-perturbative construction of inclusive collision cross-sections in the
massless Nelson model. We show that our proposal is consistent with the
standard scattering theory in the absence of the infrared problem and discuss
its status in the infrared-singular case.Comment: 23 pages, LaTeX. As appeared in Ann. Henri Poincar\'
Approach to ground state and time-independent photon bound for massless spin-boson models
It is widely believed that an atom interacting with the electromagnetic field
(with total initial energy well-below the ionization threshold) relaxes to its
ground state while its excess energy is emitted as radiation. Hence, for large
times, the state of the atom+field system should consist of the atom in its
ground state, and a few free photons that travel off to spatial infinity.
Mathematically, this picture is captured by the notion of asymptotic
completeness. Despite some recent progress on the spectral theory of such
systems, a proof of relaxation to the ground state and asymptotic completeness
was/is still missing, except in some special cases (massive photons, small
perturbations of harmonic potentials). In this paper, we partially fill this
gap by proving relaxation to an invariant state in the case where the atom is
modelled by a finite-level system. If the coupling to the field is sufficiently
infrared-regular so that the coupled system admits a ground state, then this
invariant state necessarily corresponds to the ground state. Assuming slightly
more infrared regularity, we show that the number of emitted photons remains
bounded in time. We hope that these results bring a proof of asymptotic
completeness within reach.Comment: 45 pages, published in Annales Henri Poincare. This archived version
differs from the journal version because we corrected an inconsequential
mistake in Section 3.5.1: to do this, a new paragraph was added after Lemma
3.
Ground State and Resonances in the Standard Model of Non-relativistic QED
We prove existence of a ground state and resonances in the standard model of
the non-relativistic quantum electro-dynamics (QED). To this end we introduce a
new canonical transformation of QED Hamiltonians and use the spectral
renormalization group technique with a new choice of Banach spaces.Comment: 50 pages change
Differential Redox Regulation of ORAI Ion Channels: A Mechanism to Tune Cellular Calcium Signaling
Reactive oxygen species (ROS) are involved in many physiological and pathophysiological cellular processes.
We used lymphocytes, which are exposed to highly oxidizing environments during inflammation,
to study the influence of ROS on cellular function. Calcium ion (Ca2+) influx through Ca2+ release–activated
Ca2+ (CRAC) channels composed of proteins of the ORAI family is essential for the activation, proliferation,
and differentiation of T lymphocytes, but whether and how ROS affect ORAI channel function have
been unclear. Here, we combined Ca2+ imaging, patch-clamp recordings and measurements of cell proliferation
and cytokine secretion to determine the effects of hydrogen peroxide (H2O2) on ORAI channel
activity and human T helper lymphocyte (TH cell) function. ORAI1, but not ORAI3, channels were inhibited
by oxidation by H2O2. The differential redox sensitivity of ORAI1 and ORAI3 channels depended mainly
on an extracellularly located reactive cysteine, which is absent in ORAI3. TH cells became progressively
less redox-sensitive after differentiation into effector cells, a shift that would allow them to proliferate,
differentiate, and secrete cytokines in oxidizing environments. The decreased redox sensitivity of effector
TH cells correlated with increased expression of Orai3 and increased abundance of several cytosolic antioxidants.
Knockdown of ORAI3 with small-interfering RNA rendered effector TH cells more redox-sensitive.
The differential expression of Orai isoforms between naïve and effector TH cells may tune cellular responses
under oxidative stress
Hierarchy Theory of Evolution and the Extended Evolutionary Synthesis: Some Epistemic Bridges, Some Conceptual Rifts
Contemporary evolutionary biology comprises a plural landscape of multiple co-existent conceptual frameworks and strenuous voices that disagree on the nature and scope of evolutionary theory. Since the mid-eighties, some of these conceptual frameworks have denounced the ontologies of the Modern Synthesis and of the updated Standard Theory of Evolution as unfinished or even flawed. In this paper, we analyze and compare two of those conceptual frameworks, namely Niles Eldredge’s Hierarchy Theory of Evolution (with its extended ontology of evolutionary entities) and the Extended Evolutionary Synthesis (with its proposal of an extended ontology of evolutionary processes), in an attempt to map some epistemic bridges (e.g. compatible views of causation; niche construction) and some conceptual rifts (e.g. extra-genetic inheritance; different perspectives on macroevolution; contrasting standpoints held in the “externalism–internalism” debate) that exist between them. This paper seeks to encourage theoretical, philosophical and historiographical discussions about pluralism or the possible unification of contemporary evolutionary biology
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