794 research outputs found
A solution to the hierarchy problem from an almost decoupled hidden sector within a classically scale invariant theory
If scale invariance is a classical symmetry then both the Planck scale and
the weak scale should emerge as quantum effects. We show that this can be
realized in simple scale invariant theories with a hidden sector. The
weak/Planck scale hierarchy emerges in the (technically natural) limit where
the hidden sector decouples from the ordinary sector. The weak scale is
protected from quadratic divergences because of classical scale invariance, so
there is no hierarchy problem.Comment: 10 page
Open String Amplitudes in Various Gauges
Recently, Schnabl constructed the analytic solution of the open string
tachyon. Subsequently, the absence of the physical states at the vacuum was
proved. The development relies heavily on the use of the gauge condition
different from the ordinary one. It was shown that the choice of gauge
simplifies the analysis drastically. When we perform the calculation of the
amplitudes in Schnabl gauge, we find that the off-shell amplitudes of the
Schnabl gauge is still very complicated. In this paper, we propose the use of
the propagator in the modified Schnabl gauge and show that this modified use of
the Schnabl gauge simplifies the computation of the off-shell amplitudes
drastically. We also compute the amplitudes of open superstring in this gauge.Comment: 23 pages, minor correction
The off-shell Veneziano amplitude in Schnabl gauge
We give a careful definition of the open string propagator in Schnabl gauge
and present its worldsheet interpretation. The propagator requires two
Schwinger parameters and contains the BRST operator. It builds surfaces by
gluing strips of variable width to the left and to the right of off-shell
states with contracted or expanded local frames. We evaluate explicitly the
four-point amplitude of off-shell tachyons. The computation involves a subtle
boundary term, crucial to enforce the correct exchange symmetries.
Interestingly, the familiar on-shell physics emerges even though string
diagrams produce Riemann surfaces more than once. Off-shell, the amplitudes do
not factorize over intermediate on-shell states.Comment: 48 pages, 10 figures. v2:acknowledgments adde
Note on Matrix Model with Massless Flavors
In this note, following the work of Seiberg in hep-th/0211234 for the
conjecture between the field theory and matrix model in the case with massive
fundamental flavors, we generalize it to the case with massless fundamental
flavors. We show that with a little modifications, the analysis given by
Seiberg can be used directly to the case of massless flavors. Furthermore, this
new method explains the insertion of delta functions in the matrix model given
by Demasure and Janik in hep-th/0211082.Comment: 10 pages. Type fixed. Remarks adde
Exact Superpotentials for Theories with Flavors via a Matrix Integral
We extend and test the method of Dijkgraaf and Vafa for computing the
superpotential of N=1 theories to include flavors in the fundamental
representation of the gauge group. This amounts to computing the contribution
to the superpotential from surfaces with one boundary in the matrix integral.
We compute exactly the effective superpotential for the case of gauge group
U(N_c), N_f massive flavor chiral multiplets in the fundamental and one massive
chiral multiplet in the adjoint, together with a Yukawa coupling. We compare up
to sixth-order with the result obtained by standard field theory techniques in
the already non trivial case of N_c=2 and N_f=1. The agreement is perfect.Comment: 7 pages, v2: typos involving signs fixed; v3: version to appear in
Phys.Rev.
Hearing the voices of older adult patients: processes and findings to inform health services research
Background
Clinical academic research and service improvement is planned using Patient and Public Involvement and Engagement (PPIE) but older PPIE participants are consulted less often due to the perception that they are vulnerable or hard to engage.
Objectives
To consult frail older adults about a recently adopted service, discharge to assess (D2A), and to prioritise services improvements and research topics associated with the design and delivery of discharge from hospital. To use successive PPIE processes to enable a permanent PPIE panel to be established.
Participants
Following guidance from an established hospital PPI panel 27 older adult participants were recruited. Participants from Black, Asian and Minority Ethnic (BAME) communities, affluent and non-affluent areas and varied social circumstances were included.
Methods
Focus groups and individual interviews were conducted in participants own homes or nearby social venues.
Results
Priorities for discharge included remaining independent despite often feeling lonely at home; to remain in hospital if needed; and for services to ensure effective communication with families. The main research priority identified was facilitating independence, whilst establishing a permanent PPIE panel involving older adults was viewed favourably.
Conclusions
Taking a structured approach to PPIE enabled varied older peoples’ voices to express their priorities and concerns into early discharge from hospital, as well as enabling the development of health services research into hospital discharge planning and management. Older people as participants identified research priorities after reflecting on their experiences. Listening and reflection enabled researchers to develop a new “Community PPIE Elders Panel” to create an enduring PPIE infrastructure for frail older housebound people to engage in research design, development and dissemination
Fluctuations around the Tachyon Vacuum in Open String Field Theory
We consider quadratic fluctuations around the tachyon vacuum numerically in
open string field theory. We work on a space spanned
by basis string states used in the Schnabl's vacuum solution. We show that the
truncated form of the Schnabl's vacuum solution on is
well-behaved in numerical work. The orthogonal basis for the new BRST operator
on and the quadratic forms of potentials
for independent fields around the vacuum are obtained. Our numerical results
support that the Schnabl's vacuum solution represents the minimum energy
solution for arbitrary fluctuations also in open string field theory.Comment: 16 pages, 2 figures, some comments and one table added, version to
appear in JHE
Marginal deformations in string field theory
We describe a method for obtaining analytic solutions corresponding to exact
marginal deformations in open bosonic string field theory. For the photon
marginal deformation we have an explicit analytic solution to all orders. Our
construction is based on a pure gauge solution where the gauge field is not in
the Hilbert space. We show that the solution itself is nevertheless perfectly
regular. We study its gauge transformations and calculate some coefficients
explicitly. Finally, we discuss how our method can be implemented for other
marginal deformations.Comment: 23 pages. v2: Some paragraphs improved, typos corrected, ref adde
Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity
We have analysed pion photoproduction imposing constraints from fixed t
dispersion relations and unitarity. Coupled integral equations for the S and P
wave multipoles were derived from the dispersion relations and solved by the
method of Omnes and Muskhelishvili. The free parameters were determined by a
fit to the most recent data for \pi^{+} and \pi^{0} production on the proton as
well as \pi^{-} production on the neutron, in the energy We have analysed pion
photoproduction imposing constraints from fixed t dispersion relations and
unitarity. Coupled integral equations for the S and P wave multipoles were
derived from the dispersion relations and solved by the method of Omnes and
Muskhelishvili. The free parameters were determined by a fit to the most recent
data for \pi^{+} and \pi^{0} production on the proton as well as \pi^{-}
production on the neutron, in the energy range 160 MeV \leq E_{\gamma} \leq 420
MeV. The lack of high precision data on the neutron and of polarization
observables leads to some limitations of our results. Especially the multipole
M_{1-} connected with the Roper resonance P_{11}(1440) cannot be determined to
the required precision. Our predictions for the threshold amplitudes are in
good agreement with both the data and chiral perturbation theory. In the region
of the \Delta(1232) we have determined the ratio of electric quadrupole and
magnetic dipole excitation. The position of the resonance pole is obtained in
excellent agreement with pion-nucleon scattering, and the complex residues of
the multipoles are determined with the speed-plot technique.Comment: 46 pages LATEX including 29 postscript figure
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