82 research outputs found
The strength of small-instanton amplitudes in gauge theories with compact extra dimensions
We study instanton effects in theories with compact extra dimensions. We
perform an instanton calculation in a 5d theory on a circle of radius R, with
gauge, scalar, and fermion fields in the bulk of the extra dimension. We show
that, depending on the matter content, instantons of size rho << R can dominate
the amplitude. Using deconstruction as an ultraviolet definition of the theory
allows us to show, in a controlled approximation, that for a small number of
bulk fermions, the amplitude for small size instantons exponentially grows as
e^{O(1)R/rho}.Comment: Title modified, references added, typos corrected. Version to appear
in JHEP. 24 pages, 1 figur
Index theorem for topological excitations on R^3 * S^1 and Chern-Simons theory
We derive an index theorem for the Dirac operator in the background of
various topological excitations on an R^3 \times S^1 geometry. The index
theorem provides more refined data than the APS index for an instanton on R^4
and reproduces it in decompactification limit. In the R^3 limit, it reduces to
the Callias index theorem. The index is expressed in terms of topological
charge and the eta-invariant associated with the boundary Dirac operator.
Neither topological charge nor eta-invariant is typically an integer, however,
the non-integer parts cancel to give an integer-valued index. Our derivation is
based on axial current non-conservation--an exact operator identity valid on
any four-manifold--and on the existence of a center symmetric, or approximately
center symmetric, boundary holonomy (Wilson line). We expect the index theorem
to usefully apply to many physical systems of interest, such as low temperature
(large S^1, confined) phases of gauge theories, center stabilized Yang-Mills
theories with vector-like or chiral matter (at S^1 of any size), and
supersymmetric gauge theories with supersymmetry-preserving boundary conditions
(also at any S^1). In QCD-like and chiral gauge theories, the index theorem
should shed light into the nature of topological excitations responsible for
chiral symmetry breaking and the generation of mass gap in the gauge sector. We
also show that imposing chirally-twisted boundary condition in gauge theories
with fermions induces a Chern-Simons term in the infrared. This suggests that
some QCD-like gauge theories should possess components with a topological
Chern-Simons phase in the small S^1 regime.Comment: 29 pages, refs added, published versio
Gluon condensate and c-quark mass in pseudoscalar sum rules at 3-loop order
Charmonium sum rules for pseudoscalar 0^{-+} state eta_c(1S) are analyzed
within perturbative QCD and Operator Product Expansion. The perturbative part
of the pseudoscalar correlator is considered at alpha_s^2 order and the
contribution of the gluon condensate is taken into account with alpha_s
correction. The OPE series includes the operators of dimension D=6,8 computed
both in the instanton and factorization model. The method of moments in MS-bar
scheme allows to establish acceptable values of the charm quark mass and gluon
condensate, using the experimental mass of eta_c. In result of the analisys the
charm quark mass is found to be m_c(m_c)=1.26+-0.02 GeV independently of the
condensate value. The sensitivity of the results to various approximations for
the massive 3-loop pseudoscalar correlator is discussed.Comment: 19 pages, 1 latex + 5 eps files. v2: Operators of dimension D=8
included; the condensate restriction relaxed; c-quark mass is found
m_c(m_c)=1.26+-0.02 GeV independently of other sum rules and condensate
value. To appear in JHE
Infinite Renormalization of Theta-Term and Jarlskog Invariant for CP-Violation
The logarithmic ultraviolet divergence in the theta-term induced by
electroweak interactions in the Kobayashi-Maskawa model of CP-violation, found
by Ellis and Gaillard, is discussed. We relate it to the Jarlskog CP-odd
invariant of quark mass matrix. The divergence arises in 14th order in Higgs
coupling as well as in 12th order plus 2nd order in U(1) gauge boson coupling.Comment: 6 pages + 1 figure (included), LaTex, TPI-MINN-93/91-T,
UMN-TH-1212/9
Effective Lagrangian and Quantum Screening in Charged Condensate
A condensate of charged scalars in a neutralizing background of fermions
(e.g., condensed helium-4 nuclei in an electron background in white dwarf
cores) is investigated further. We discuss an effective Lagrangian approach to
this system and show that the strong screening of an electric charge found
previously in arXiv:0806.3692 in a mean-field approximation, is a consequence
of a cancellation due to a phonon. The resulting propagators contain terms that
strongly modify their infrared behavior. Furthermore, we evaluate a one-loop
fermion quantum correction to the screened potential, and find that it is also
suppressed by the phonon subtraction. Therefore, charged impurities (e.g.,
hydrogen or helium-3 nuclei) will be screened efficiently by the condensate.Comment: 1+16 pages; v2: typos & minor improvements; v3: one reference and one
footnote added; two comments streamline
Nonperturbative Corrections to Inclusive Beauty and Charm Decays: QCD versus Phenomenological Models
We present a selfconsistent method for treating nonperturbative effects in
inclusive nonleptonic and semileptonic decays of heavy flavour hadrons. These
effects give rise to powerlike corrections , with
denoting the heavy quark mass.The leading correction to the semileptonic
branching ratio occurs for n=2. It is expressed in terms of the
vector-pseudoscalar mass splitting: \delta BR\ind{sl}/BR\ind{sl} \simeq
BR\ind{nl}\, \cdot \,6\,(\,(M_V^2-M_P^2)/m_Q^2)\cdot (c_+^2 - c_-^2)/2N_c and
yields a {\it reduction} of BR\ind{sl}. This nonperturbative correction
contributes to the nonleptonic width with a sign opposite to that of the
perturbative terms that are non-leading in . In beauty decays the former
reduces the latter by 20 \% whereas in charm decays they more or less cancel.
This leads to a {\it reduction} of BR\ind{sl} by no more than 10 \% in beauty
decays and by a factor of roughly two in charm decays. We confront these
results with those obtained from phenomenological models of heavy flavour
decays and find that such models are unable to mimic these leading corrections
by a specific choice of quark masses or by invoking Fermi motion.Comment: 11 pages (2 figs are not included), Latex file, FERMILAB-PUB-92/158-T
UND-HEP-92-BIG04 TPI-MINN-92/30-
On Conformal Deformations
For a conformal theory it is natural to seek the conformal moduli space, M_c
to which it belongs, generated by the exactly marginal deformations. By now we
should have the tools to determine M_c in the presence of enough supersymmetry.
Here it is shown that its dimension is determined in terms of a certain index.
Moreover, the D-term of the global group is an obstruction for deformation, in
presence of a certain amount of preserved supersymmetry. As an example we find
that the deformations of the membrane (3d) field theory, under certain
conditions, are in 35/SL(4,C). Other properties including the local geometry of
M_c are discussed.Comment: 10 page
A Remark on Lorentz Violation at Finite Temperature
We investigate the radiatively induced Chern-Simons-like term in
four-dimensional field theory at finite temperature. The Chern-Simons-like term
is temperature dependent and breaks the Lorentz and CPT symmetries. We find
that this term remains undetermined although it can be found unambiguously in
different regularization schemes at finite temperature.Comment: To appear in JHEP, 8 pages, 1 eps figure, minor changes and
references adde
On search for new Higgs physics in CDF at the Tevatron
We discuss the Higgs boson mass sum rules in the Minimal Supersymmetric
Standard Model in order to estimate the upper limits on the masses of stop
quarks as well as the lower bounds on the masses of the scalar Higgs boson
state. The bounds on the scale of quark-lepton compositeness derived from the
CDF Collaboration (Fermilab Tevatron) data and applied to new extra gauge boson
search is taken into account. These extra gauge bosons are considered in the
framework of the extended SU(2)_h \times SU(2)_l model. In addition, we discuss
the physics of rare decays of the MSSM Higgs bosons in both CP-even and CP-odd
sectors and also some extra gauge bosons.Comment: 24 pages, LaTeX, 8 figure
Strong coupling in massive gravity by direct calculation
We consider four-dimensional massive gravity with the Fierz-Pauli mass term.
The analysis of the scalar sector has revealed recently that this theory
becomes strongly coupled above the energy scale \Lambda = (M_{Pl}^2 m^4)^{1/5}
where m is the mass of the graviton. We confirm this scale by explicit
calculations of the four-graviton scattering amplitude and of the loop
correction to the interaction between conserved sources.Comment: 9 pages, 3 figures, some clarifications adde
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