391 research outputs found
Geometrical properties of Riemannian superspaces, observables and physical states
Classical and quantum aspects of physical systems that can be described by
Riemannian non degenerate superspaces are analyzed from the topological and
geometrical points of view. For the N=1 case the simplest supermetric
introduced in [Physics Letters B \textbf{661}, (2008),186] have the correct
number of degrees of freedom for the fermion fields and the super-momentum
fulfil the mass shell condition, in sharp contrast with other cases in the
literature where the supermetric is degenerate. This fact leads a deviation of
the 4-impulse (e.g. mass constraint) that can be mechanically interpreted as a
modification of the Newton's law. Quantum aspects of the physical states and
the basic states and the projection relation between them, are completely
described due the introduction of a new Majorana-Weyl representation of the
generators of the underlying group manifold. A new oscillatory fermionic effect
in the part of the vaccum solution involving the chiral and antichiral
components of this Majorana bispinor is explicitly shown.Comment: 16 pags. 3 figures. To Anna Grigorievna Kartavenko and Academic
Professor Alexei Norianovich Sissakian, in memoria
Confinement-Deconfinement Transition in 3-Dimensional QED
We argue that, at finite temperature, parity invariant non-compact
electrodynamics with massive electrons in 2+1 dimensions can exist in both
confined and deconfined phases. We show that an order parameter for the
confinement-deconfinement phase transition is the Polyakov loop operator whose
average measures the free energy of a test charge that is not an integral
multiple of the electron charge. The effective field theory for the Polyakov
loop operator is a 2-dimensional Euclidean scalar field theory with a global
discrete symmetry , the additive group of the integers. We argue that the
realization of this symmetry governs confinement and that the
confinement-deconfinement phase transition is of
Berezinskii-Kosterlitz-Thouless type. We compute the effective action to
one-loop order and argue that when the electron mass is much greater than
the temperature and dimensional coupling , the effective field theory
is the Sine-Gordon model. In this limit, we estimate the critical temperature,
.Comment: 11 pages, latex, no figure
Gravitational anomaly and fundamental forces
I present an argument, based on the topology of the universe, why there are
three generations of fermions. The argument implies a preferred gauge group of
SU(5), but with SO(10) representations of the fermions. The breaking pattern
SU(5) to SU(3)xSU(2)xU(1) is preferred over the pattern SU(5) to SU(4)xU(1). On
the basis of the argument one expects an asymmetry in the early universe
microwave data, which might have been detected already.Comment: Contribution to the 2nd School and Workshop on Quantum Gravity and
Quantum Geometry. Corfu, september 13-20 2009. 10 page
The cosmological background of vector modes
We investigate the spectrum of vector modes today which is generated at
second order by density perturbations. The vector mode background that is
generated by structure formation is small but in principle it contributes to
the integrated Sachs-Wolfe effect, to redshift-space distortions and to weak
lensing. We recover, clarify and extend previous results, and explain carefully
why no vorticity is generated in the fluid at second order. The amplitude of
the induced vector mode in the metric is around 1% that of the first-order
scalars on small scales. We also calculate the power spectrum and the energy
density of the vector part of the shear at second order.Comment: 9 pages, 2 figures. Version to appear in JCAP; minor improvements and
additional reference
Cosmological Non-Linearities as an Effective Fluid
The universe is smooth on large scales but very inhomogeneous on small
scales. Why is the spacetime on large scales modeled to a good approximation by
the Friedmann equations? Are we sure that small-scale non-linearities do not
induce a large backreaction? Related to this, what is the effective theory that
describes the universe on large scales? In this paper we make progress in
addressing these questions. We show that the effective theory for the
long-wavelength universe behaves as a viscous fluid coupled to gravity:
integrating out short-wavelength perturbations renormalizes the homogeneous
background and introduces dissipative dynamics into the evolution of
long-wavelength perturbations. The effective fluid has small perturbations and
is characterized by a few parameters like an equation of state, a sound speed
and a viscosity parameter. These parameters can be matched to numerical
simulations or fitted from observations. We find that the backreaction of
small-scale non-linearities is very small, being suppressed by the large
hierarchy between the scale of non-linearities and the horizon scale. The
effective pressure of the fluid is always positive and much too small to
significantly affect the background evolution. Moreover, we prove that
virialized scales decouple completely from the large-scale dynamics, at all
orders in the post-Newtonian expansion. We propose that our effective theory be
used to formulate a well-defined and controlled alternative to conventional
perturbation theory, and we discuss possible observational applications.
Finally, our way of reformulating results in second-order perturbation theory
in terms of a long-wavelength effective fluid provides the opportunity to
understand non-linear effects in a simple and physically intuitive way.Comment: 84 pages, 3 figure
Electroweak Corrections to the Charged Higgs Boson Decay into Chargino and Neutralino
The electroweak corrections to the partial widths of the decays including one-loop
diagrams of the third generation quarks and squarks, are investigated within
the Supersymmetric Standard Model. The relative corrections can reach the
values about 10%, therefore they should be taken into account for the precise
experimental measurement at future colliders.Comment: 21 pages, 6 eps figures, 1 Latex fil
Global conformal anomaly in N=2 string
We show the existence of a global anomaly in the one-loop graphs of N=2
string theory, defined by sewing tree amplitudes, unless spacetime
supersymmetry is imposed. The anomaly is responsible for the non-vanishing
maximally helicity violating amplitudes. The supersymmetric completion of the
N=2 string spectrum is formulated by extending the previous cohomological
analysis with an external spin factor; the target space-time spin-statistics of
these individual fields in a selfdual background are compatible with previous
cohomological analysis as fields of arbitrary spin may be bosonized into one
another. We further analyze duality relations between the open and closed
string amplitudes and demonstrate this in the supersymmetric extension of the
target space-time theory through the insertion of zero-momentum operators.Comment: 29 pages, LaTeX, one figur
Two-loop scalar self-energies in a general renormalizable theory at leading order in gauge couplings
I present results for the two-loop self-energy functions for scalars in a
general renormalizable field theory, using mass-independent renormalization
schemes based on dimensional regularization and dimensional reduction. The
results are given in terms of a minimal set of loop-integral basis functions,
which are readily evaluated numerically by computers. This paper contains the
contributions corresponding to the Feynman diagrams with zero or one vector
propagator lines. These are the ones needed to obtain the pole masses of the
neutral and charged Higgs scalar bosons in supersymmetry, neglecting only the
purely electroweak parts at two-loop order. A subsequent paper will present the
results for the remaining diagrams, which involve two or more vector lines.Comment: 26 pages, 4 figures, revtex4, axodraw.sty. Version 2: sentence after
eq. (A.13) corrected, references added. Version 3: typos in eqs. (5.17),
(5.20), (5.21), (5.32) are corrected. Also, the MSbar versions of eqs. (5.32)
and (5.33) are now include
The impact of the rising colorectal cancer incidence in young adults on the optimal age to start screening
BACKGROUND: In 2016, the Microsimulation Screening Analysis-Colon (MISCAN-Colon) model was used to inform the US Preventive Services Task Force colorectal cancer (CRC) screening guidelines. In this study, 1 of 2 microsimulation analyses to inform the update of the American Cancer Society CRC screening guideline, the authors re-evaluated the optimal screening strategies in light of the increase in CRC diagnosed in young adults. METHODS: The authors adjusted the MISCAN-Colon model to reflect the higher CRC incidence in young adults, who were assumed to carry forward escalated disease risk as they age. Life-years gained (LYG; benefit), the number of colonoscopies (COL; burden) and the ratios of incremental burden to benefit (efficiency ratio [ER] = ΔCOL/ΔLYG) were projected for different screening strategies. Strategies differed with respect to test modality, ages to start (40 years, 45 years, and 50 years) and ages to stop (75 years, 80 years, and 85 years) screening, and screening intervals (depending on screening modality). The authors then determined the model-recommended strategies in a similar way as was done for the US Preventive Services Task Force, using ER thresholds in accordance with the previously accepted ER of 39. RESULTS: Because of the higher CRC incidence, model-predicted LYG from screening increased compared with the previous analyses. Consequently, the balance of burden to benefit of screening improved and now 10-yearly colonoscopy screening starting at age 4
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