152 research outputs found
Trying to understand the Standard Model parameters
We stress the importance of the circa 20 parameters in the Standard Model,
which are not fixed by the model but only determined experimentally, as a
window to the physics beyond the Standard Model. However, it is a tiny window
in as far as these numbers contain only the information corresponding to about
one line of text. Looking for a method to study these coupling and mass
parameters, we put forward the idea of the Multiple Point Principle as a first
step. This principle states that Nature adjusts the coupling and mass
parameters so as to make many different vacuum states exist and have
approximately the same energy densities (cosmological constants). As an
illustrative application, we put up the proposal that a small increase (maybe
only an infinitesimal one) in the value of the top quark coupling constant
could lead to a new vacuum phase; in this new phase the binding of a bound
state of 6 top quarks and 6 anti-top quarks becomes so strong as to become a
tachyon and condense in the vacuum. Assuming the existence of a third
degenerate vacuum at the fundamental energy scale, we present a solution to the
hierarchy problem of why the ratio of the fundamental scale to the electroweak
scale is so large. We also present a 5 parameter fit to the orders of magnitude
of the quark-lepton masses and mixing angles in the Family Replicated Gauge
Group Model. In this model, the Standard Model gauge group and a gauged B-L
(baryon number minus lepton number) is extended to one set of gauge fields for
each family of fermions.Comment: Institute address corrected and one reference adde
Unifying CP violations of quark and lepton sectors
A preliminary determination of the Dirac phase in the PMNS matrix is
\dell\approx -\frac{\pi}{2}. A rather accurately determined Jarlskog
invariant in the CKM matrix is close to the maximum. Since the phases in
the CKM and PMNS matrices will be accurately determined in the future, it is an
interesting problem to relate these two phases. This can be achieved in a
families-unified grand unification if the weak CP violation is introduced
spontaneously {\it \`a la} Froggatt and Nielsen at a high energy scale, where
only one meaningful Dirac CP phase appears.Comment: 10 pages with 3 figure
The Hilbert basis method for D-flat directions and the superpotential
We discuss, using the Hilbert basis method, how to efficiently construct a
complete basis for D-flat directions in supersymmetric Abelian and non-Abelian
gauge theories. We extend the method to discrete (R and non-R) symmetries. This
facilitates the construction of a basis of all superpotential terms in a theory
with given symmetries.Comment: 11 pages; a related mathematica code can be found at
http://einrichtungen.ph.tum.de/T30e/codes/NonAbelianHilbert
On The Potential of Minimal Flavour Violation
Assuming the Minimal Flavour Violation hypothesis, we derive the general
scalar potential for fields whose background values are the Yukawa couplings.
We analyze the minimum of the potential and discuss the fine-tuning required to
dynamically generate the mass hierarchies and the mixings between different
quark generations. Two main cases are considered, corresponding to Yukawa
interactions being effective operators of dimension five or six (or,
equivalently, resulting from bi-fundamental and fundamental scalar fields,
respectively). At the renormalizable and classical level, no mixing is
naturally induced from dimension five Yukawa operators. On the contrary, from
dimension six Yukawa operators one mixing angle and a strong mass hierarchy
among the generations result.Comment: 33 pages, 6 figures; Note added in proof on the stability of the
minima of the scalar potential; results unchanged; references adde
D-brane Inspired Fermion Mass Textures
In this paper, the issues of the quark mass hierarchies and the Cabbibo
Kobayashi Maskawa mixing are analyzed in a class of intersecting D-brane
configurations with Standard Model gauge symmetry. The relevant mass matrices
are constructed taking into account the constraints imposed by extra abelian
symmetries and anomaly cancelation conditions. Possible mass generating
mechanisms including perturbative as well as non-perturbative effects are
discussed and specific patterns of mass textures are found characterized by the
hierarchies of the scales where the various sources contribute. It is argued
that the Cholesky decomposition of the mass matrices is the most appropriate
way to determine the properties of these fermion mass patterns, while the
associated triangular mass matrix form provides a unified description of all
phenomenologically equivalent symmetric and non-symmetric mass matrices. An
elegant analytic formula is derived for the Cholesky triangular form of the
mass matrices where the entries are given as simple functions of the mass
eigenstates and the diagonalizing transformation entries. Finally, motivated by
the possibility of vanishing zero Yukawa mass entries in several D-brane and
F-theory constructions due to the geometry of the internal space, we analyse in
detail all possible texture-zeroes mass matrices within the proposed new
context. These new texture-zeroes are compared to those existing in the
literature while D-brane inspired cases are worked out in detail.Comment: 58 pages, 7 figure
Ultraviolet Completion of Flavour Models
Effective Flavour Models do not address questions related to the nature of
the fundamental renormalisable theory at high energies. We study the
ultraviolet completion of Flavour Models, which in general has the advantage of
improving the predictivity of the effective models. In order to illustrate the
important features we provide minimal completions for two known A4 models. We
discuss the phenomenological implications of the explicit completions, such as
lepton flavour violating contributions that arise through the exchange of
messenger fields.Comment: 18 pages, 8 figure
Effective Lagrangian approach to vector mesons, their structure and decays
An improved update of the structure and decays of , and
mesons based on a chiral SU(3) Lagrangian, including anomaly terms is
presented. We demonstrate that a consistent and quantitatively successful
description of both pion and kaon electromagnetic form factors can be achieved.
We also discuss the cross section, the Dalitz
decay and aspects of and mixing. Relations to previous versions of the Vector Meson Dominance
model will be examined.Comment: 35 pages, TeX, 14 ps figures, submitted to Z.Phys.
Vacuum Alignment in SUSY A4 Models
In this note we discuss the vacuum alignment in supersymmetric models with
spontaneously broken flavour symmetries in the presence of soft supersymmetry
(SUSY) breaking terms. We show that the inclusion of soft SUSY breaking terms
can give rise to non-vanishing vacuum expectation values (VEVs) for the
auxiliary components of the flavon fields. These non-zero VEVs can have an
important impact on the phenomenology of this class of models, since they can
induce an additional flavour violating contribution to the sfermion soft mass
matrix of right-left (RL) type. We carry out an explicit computation in a class
of SUSY A4 models predicting tri-bimaximal mixing in the lepton sector. The
flavour symmetry breaking sector is described in terms of flavon and driving
supermultiplets. We find non-vanishing VEVs for the auxiliary components of the
flavon fields and for the scalar components of the driving fields which are of
order m_{SUSY} x and m_{SUSY}, respectively. Thereby, m_{SUSY} is the
generic soft SUSY breaking scale which is expected to be around 1 TeV and
is the VEV of scalar components of the flavon fields. Another effect of these
VEVs can be the generation of a mu term.Comment: 23 pages; added a new section on the relation to Supergravity;
version accepted for publication in JHE
Implementing a quality improvement programme in palliative care in care homes: a qualitative study
<p>Abstract</p> <p>Background</p> <p>An increasing number of older people reach the end of life in care homes. The aim of this study is to explore the perceived benefits of, and barriers to, implementation of the Gold Standards Framework for Care Homes (GSFCH), a quality improvement programme in palliative care.</p> <p>Methods</p> <p>Nine care homes involved in the GSFCH took part. We conducted semi-structured interviews with nine care home managers, eight nurses, nine care assistants, eleven residents and seven of their family members. We used the Framework approach to qualitative analysis. The analysis was deductive based on the key tasks of the GSFCH, the 7Cs: communication, coordination, control of symptoms, continuity, continued learning, carer support, and care of the dying. This enabled us to consider benefits of, and barriers to, individual components of the programme, as well as of the programme as a whole.</p> <p>Results</p> <p>Perceived benefits of the GSFCH included: improved symptom control and team communication; finding helpful external support and expertise; increasing staff confidence; fostering residents' choice; and boosting the reputation of the home. Perceived barriers included: increased paperwork; lack of knowledge and understanding of end of life care; costs; and gaining the cooperation of GPs. Many of the tools and tasks in the GSFCH focus on improving communication. Participants described effective communication within the homes, and with external providers such as general practitioners and specialists in palliative care. However, many had experienced problems with general practitioners. Although staff described the benefits of supportive care registers, coding predicted stage of illness and advance care planning, which included improved communication, some felt the need for more experience of using these, and there were concerns about discussing death.</p> <p>Conclusions</p> <p>Most of the barriers described by participants are relevant to other interventions to improve end of life care in care homes. There is a need to investigate the impact of quality improvement programmes in care homes, such as the GSFCH, on a wider range of outcomes for residents and their families, and to monitor the sustainability of any resulting improvements. It is also important to explore the impact of the different components of these complex interventions.</p
The flavor puzzle in multi-Higgs models
We reconsider the flavor problem in the models with two Higgs doublets. By
studying two generation toy models, we look for flavor basis independent
constraints on Yukawa couplings that will give us the mass hierarchy while
keeping all Yukawa couplings of the same order. We then generalize our findings
to the full three generation Standard Model. We find that we need two
constraints on the Yukawa couplings to generate the observed mass hierarchy,
and a slight tuning of Yukawa couplings of order 10%, much less than the
Standard Model. We briefly study how these constraints can be realized, and
show how flavor changing currents are under control for mixing in
the near-decoupling limit.Comment: 26 pages, typos are corrected, references are added, the final
versio
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