535 research outputs found
Reconstitution of T cell receptor signaling in ZAP-70-deficient cells by retroviral transduction of the ZAP-70 gene.
A variant of severe combined immunodeficiency syndrome (SCID) with a selective inability to produce CD8 single positive T cells and a signal transduction defect in peripheral CD4+ cells has recently been shown to be the result of mutations in the ZAP-70 gene. T cell receptor (TCR) signaling requires the association of the ZAP-70 protein tyrosine kinase with the TCR complex. Human T cell leukemia virus type I-transformed CD4+ T cell lines were established from ZAP-70-deficient patients and normal controls. ZAP-70 was expressed and appropriately phosphorylated in normal T cell lines after TCR engagement, but was not detected in T cell lines from ZAP-70-deficient patients. To determine whether signaling could be reconstituted, wild-type ZAP-70 was introduced into deficient cells with a ZAP-70 retroviral vector. High titer producer clones expressing ZAP-70 were generated in the Gibbon ape leukemia virus packaging line PG13. After transduction, ZAP-70 was detected at levels equivalent to those observed in normal cells, and was appropriately phosphorylated on tyrosine after receptor engagement. The kinase activity of ZAP-70 in the reconstituted cells was also appropriately upregulated by receptor aggregation. Moreover, normal and transduced cells, but not ZAP-70-deficient cells, were able to mobilize calcium after receptor ligation, indicating that proximal TCR signaling was reconstituted. These results indicate that this form of SCID may be corrected by gene therapy
Four-nucleon contact interactions from holographic QCD
We calculate the low energy constants of four-nucleon interactions in an
effective chiral Lagrangian in holographic QCD. We start with a D4-D8 model to
obtain meson-nucleon interactions and then integrate out massive mesons to
obtain the four-nucleon interactions in 4D. We end up with two low energy
constants at the leading order and seven of them at the next leading order,
which is consistent with the effective chiral Lagrangian. The values of the low
energy constants are evaluated with the first five Kaluza-Klein resonances.Comment: 28 page
Effective Theory of a Dynamically Broken Electroweak Standard Model at NLO
We consider the Standard Model as an effective theory at the weak scale
of a generic new strong interaction that dynamically breaks electroweak
symmetry at the energy scale (few) TeV. Assuming only the
minimal field content with the Standard Model fermions and gauge bosons, but
without a light Higgs particle, we construct the complete Lagrangian through
next-to-leading order, that is, including terms of order . The
systematics behind this expansion is clarified. Although similar to chiral
perturbation theory, it is not governed by the dimension of operators alone,
but depends in an essential way on the loop expansion. Power-counting formulas
are derived that indicate the classes of operators required at the
next-to-leading order. The complete set of operators at leading and
next-to-leading order is then listed, based on the restrictions implied by the
Standard-Model gauge symmetries. We recover the well-known operators discussed
in the literature in connection with the electroweak chiral Lagrangian and in
similar contexts, but we collect a complete and systematic list of all terms
through order . This includes some operators not discussed in
explicit terms before. We also show that a few of the previously considered
operators can be eliminated via the equations of motion. As another important
result we confirm the known list of dimension-6 operators in the Standard Model
with an elementary Higgs doublet, essentially as a special case of our
scenario.Comment: 35 pages, 1 figure; references adde
Theoretical Constraints on the Higgs Effective Couplings
We derive constraints on the sign of couplings in an effective Higgs
Lagrangian using prime principles such as the naturalness principle, global
symmetries, and unitarity. Specifically, we study four dimension-six operators,
O_H, O_y, O_g, and O_gamma, which contribute to the production and decay of the
Higgs boson at the Large Hadron Collider (LHC), among other things. Assuming
the Higgs is a fundamental scalar, we find: 1) the coefficient of O_H is
positive except when there are triplet scalars, resulting in a reduction in the
Higgs on-shell coupling from their standard model (SM) expectations if no other
operators contribute, 2) the linear combination of O_H and O_y controlling the
overall Higgs coupling to fermion is always reduced, 3) the sign of O_g induced
by a new colored fermion is such that it interferes destructively with the SM
top contribution in the gluon fusion production of the Higgs, if the new
fermion cancels the top quadratic divergence in the Higgs mass, and 4) the
correlation between naturalness and the sign of O_gamma is similar to that of
O_g, when there is a new set of heavy electroweak gauge bosons. Next
considering a composite scalar for the Higgs, we find the reduction in the
on-shell Higgs couplings persists. If further assuming a collective breaking
mechanism as in little Higgs theories, the coefficient of O_H remains positive
even in the presence of triplet scalars. In the end, we conclude that the gluon
fusion production of the Higgs boson is reduced from the SM rate in all
composite Higgs models. Our study suggests a wealth of information could be
revealed by precise measurements of the Higgs couplings, providing strong
motivations for both improving on measurements at the LHC and building a
precision machine such as the linear collider.Comment: 37 pages, one figure; v2: improved discussion on dispersion relation
and other minor modifications; version accepted for publication
Quantum Gravity in Everyday Life: General Relativity as an Effective Field Theory
This article is meant as a summary and introduction to the ideas of effective
field theory as applied to gravitational systems.
Contents:
1. Introduction
2. Effective Field Theories
3. Low-Energy Quantum Gravity
4. Explicit Quantum Calculations
5. ConclusionsComment: 56 pages, 2 figures, JHEP style, Invited review to appear in Living
Reviews of Relativit
WIMP-nucleus scattering in chiral effective theory
We discuss long-distance QCD corrections to the WIMP-nucleon(s) interactions
in the framework of chiral effective theory. For scalar-mediated WIMP-quark
interactions, we calculate all the next-to-leading-order corrections to the
WIMP-nucleus elastic cross-section, including two-nucleon amplitudes and
recoil-energy dependent shifts to the single-nucleon scalar form factors. As a
consequence, the scalar-mediated WIMP-nucleus cross-section cannot be
parameterized in terms of just two quantities, namely the neutron and proton
scalar form factors at zero momentum transfer, but additional parameters
appear, depending on the short-distance WIMP-quark interaction. Moreover,
multiplicative factorization of the cross-section into particle, nuclear and
astro-particle parts is violated. In practice, while the new effects are of the
natural size expected by chiral power counting, they become very important in
those regions of parameter space where the leading order WIMP-nucleus amplitude
is suppressed, including the so-called "isospin-violating dark matter" regime.
In these regions of parameter space we find order-of-magnitude corrections to
the total scattering rates and qualitative changes to the shape of recoil
spectra.Comment: 23 pages, 6 figures, 1 tabl
Two-nucleon problem in semi-relativistic baryon chiral perturbation theory
We consider a symmetry-preserving approach to the nucleon-nucleon scattering
problem in the framework of the higher-derivative formulation of baryon chiral
perturbation theory. Within this framework the leading-order amplitude is
calculated by solving renormalizable equations and corrections are taken into
account perturbatively.Comment: 3 pages, talk given at 20th European Conference on Few-Body Problems
in Physics (EFB 20), Pisa, Italy, 10-14 Sep 200
Minimal Conformal Technicolor and Precision Electroweak Tests
We study the minimal model of conformal technicolor, an SU(2) gauge theory
near a strongly coupled conformal fixed point, with conformal symmetry softly
broken by technifermion mass terms. Conformal symmetry breaking triggers chiral
symmetry breaking in the pattern SU(4) -> Sp(4), which gives rise to a
pseudo-Nambu-Goldstone boson that can act as a composite Higgs boson. The top
quark is elementary, and the top and electroweak gauge loop contributions to
the Higgs mass are cut off entirely by Higgs compositeness. In particular, the
model requires no top partners and no "little Higgs" mechanism. A nontrivial
vacuum alignment results from the interplay of the top loop and technifermion
mass terms. The composite Higgs mass is completely determined by the top loop,
in the sense that m_h/m_t is independent of the vacuum alignment and is
computable by a strong-coupling calculation. There is an additional composite
pseudoscalar A with mass larger than m_h and suppressed direct production at
LHC. We discuss the electroweak fit in this model in detail. Corrections to Z
-> bb and the T parameter from the top sector are suppressed by the enhanced
Sp(4) custodial symmetry. Even assuming that the strong contribution to the S
parameter is positive and usuppressed, a good electroweak fit can be obtained
for v/f ~ 0.25, where v and f are the electroweak and chiral symmetry breaking
scales respectively. This requires fine tuning at the 10% level.Comment: 34 pages, 4 figures; v2: updated precision electroweak fi
Flavor in Minimal Conformal Technicolor
We construct a complete, realistic, and natural UV completion of minimal
conformal technicolor that explains the origin of quark and lepton masses and
mixing angles. As in "bosonic technicolor", we embed conformal technicolor in a
supersymmetric theory, with supersymmetry broken at a high scale. The exchange
of heavy scalar doublets generates higher-dimension interactions between
technifermions and quarks and leptons that give rise to quark and lepton masses
at the TeV scale. Obtaining a sufficiently large top quark mass requires strong
dynamics at the supersymmetry breaking scale in both the top and technicolor
sectors. This is natural if the theory above the supersymmetry breaking also
has strong conformal dynamics. We present two models in which the strong top
dynamics is realized in different ways. In both models, constraints from
flavor-changing effects can be easily satisfied. The effective theory below the
supersymmetry breaking scale is minimal conformal technicolor with an
additional light technicolor gaugino. We argue that this light gaugino is a
general consequence of conformal technicolor embedded into a supersymmetric
theory. If the gaugino has mass below the TeV scale it will give rise to an
additional pseudo Nambu-Goldstone boson that is observable at the LHC.Comment: 37 pages; references adde
QCD axion and quintessential axion
The axion solution of the strong CP problem is reviewed together with the
other strong CP solutions. We also point out the quintessential
axion(quintaxion) whose potential can be extremely flat due to the tiny ratio
of the hidden sector quark mass and the intermediate hidden sector scale. The
quintaxion candidates are supposed to be the string theory axions, the model
independent or the model dependent axions.Comment: 15 pages. Talk presented at Castle Ringberg, June 9-14, 200
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