597 research outputs found
Evidence for the Multiverse in the Standard Model and Beyond
In any theory it is unnatural if the observed parameters lie very close to
special values that determine the existence of complex structures necessary for
observers. A naturalness probability, P, is introduced to numerically evaluate
the unnaturalness. If P is small in all known theories, there is an observer
naturalness problem. In addition to the well-known case of the cosmological
constant, we argue that nuclear stability and electroweak symmetry breaking
(EWSB) represent significant observer naturalness problems. The naturalness
probability associated with nuclear stability is conservatively estimated as
P_nuc < 10^{-(3-2)}, and for simple EWSB theories P_EWSB < 10^{-(2-1)}. This
pattern of unnaturalness in three different arenas, cosmology, nuclear physics,
and EWSB, provides evidence for the multiverse. In the nuclear case the problem
is largely solved even with a flat multiverse distribution, and with nontrivial
distributions it is possible to understand both the proximity to neutron
stability and the values of m_e and m_d - m_u in terms of the electromagnetic
contribution to the proton mass. It is reasonable that multiverse distributions
are strong functions of Lagrangian parameters due to their dependence on
various factors. In any EWSB theory, strongly varying distributions typically
lead to a little or large hierarchy, and in certain multiverses the size of the
little hierarchy is enhanced by a loop factor. Since the correct theory of EWSB
is unknown, our estimate for P_EWSB is theoretical. The LHC will determine
P_EWSB more robustly, which may remove or strengthen the observer naturalness
problem of EWSB. For each of the three arenas, the discovery of a natural
theory would eliminate the evidence for the multiverse; but in the absence of
such a theory, the multiverse provides a provisional understanding of the data.Comment: 79 pages, 23 figure
Landscape Predictions for the Higgs Boson and Top Quark Masses
If the Standard Model is valid up to scales near the Planck mass, and if the
cosmological constant and Higgs mass parameters scan on a landscape of vacua,
it is well known that the observed orders of magnitude of these quantities can
be understood from environmental selection for large-scale structure and atoms.
If in addition the Higgs quartic coupling scans, with a probability
distribution peaked at low values, environmental selection for a phase having a
scale of electroweak symmetry breaking much less than the Planck scale leads to
a most probable Higgs mass of 106 GeV. While fluctuations below this are
negligible, the upward fluctuation is 25/p GeV, where p measures the strength
of the peaking of the a priori distribution of the quartic coupling. If the top
Yukawa coupling also scans, the most probable top quark mass is predicted to
lie in the range (174--178) GeV, providing the standard model is valid to at
least 10^{17} GeV. The downward fluctuation is 35 GeV/ \sqrt{p}, suggesting
that p is sufficiently large to give a very precise Higgs mass prediction.
While a high reheat temperature after inflation could raise the most probable
value of the Higgs mass to 118 GeV, maintaining the successful top prediction
suggests that reheating is limited to about 10^8 GeV, and that the most
probable value of the Higgs mass remains at 106 GeV. If all Yukawa couplings
scan, then the e,u,d and t masses are understood to be outliers having extreme
values induced by the pressures of strong environmental selection, while the s,
\mu, c, b, \tau Yukawa couplings span only two orders of magnitude, reflecting
an a priori distribution peaked around 10^{-3}. Extensions of these ideas allow
order of magnitude predictions for neutrino masses, the baryon asymmetry and
important parameters of cosmological inflation.Comment: 41 pages; v4: threshold corrrections for top Yukawa are correcte
Multiverse Understanding of Cosmological Coincidences
There is a deep cosmological mystery: although dependent on very different
underlying physics, the timescales of structure formation, of galaxy cooling
(both radiatively and against the CMB), and of vacuum domination do not differ
by many orders of magnitude, but are all comparable to the present age of the
universe. By scanning four landscape parameters simultaneously, we show that
this quadruple coincidence is resolved. We assume only that the statistical
distribution of parameter values in the multiverse grows towards certain
catastrophic boundaries we identify, across which there are drastic regime
changes. We find order-of-magnitude predictions for the cosmological constant,
the primordial density contrast, the temperature at matter-radiation equality,
the typical galaxy mass, and the age of the universe, in terms of the fine
structure constant and the electron, proton and Planck masses. Our approach
permits a systematic evaluation of measure proposals; with the causal patch
measure, we find no runaway of the primordial density contrast and the
cosmological constant to large values.Comment: 40 pages, 5 figures; discussion of measures extended, version to
appear in Phys. Rev.
The case of veterinary interprofessional practice: From one health to a world of its own
BACKGROUND: Research regarding the veterinary professions' involvement in interprofessional practice and education (IPE), either with health care professionals as part of One Health, or specifically within the veterinary health care team, is sparse. PURPOSE: To investigate veterinary interprofessional working and learning in veterinary practices; then ultimately to make recommendations for IPE. METHOD: Two case studies in typical but contrasting practices were conducted. The study consisted of three sequential and complementary weeks: 1) observing the whole team, 2) shadowing selected focus individuals from each profession and 3) interviewing focus individuals regarding teamwork. Triangulation was achieved by synthesis of emergent themes from observational field notes and interview transcripts. DISCUSSION: Facilitators to interprofessional practices included hierarchy, trust and value, different perspectives, formal infrastructure and professionalization. Challenges included hierarchy, spatial and temporal work patterns, professional motivations, and error and blame. CONCLUSION: The veterinary and human health care fields face similar interprofessional challenges. Real life observations, as described here, can provide important insight relevant to the design of IPE initiatives
Metric-affine f(R) theories of gravity
General Relativity assumes that spacetime is fully described by the metric
alone. An alternative is the so called Palatini formalism where the metric and
the connections are taken as independent quantities. The metric-affine theory
of gravity has attracted considerable attention recently, since it was shown
that within this framework some cosmological models, based on some generalized
gravitational actions, can account for the current accelerated expansion of the
universe. However we think that metric-affine gravity deserves much more
attention than that related to cosmological applications and so we consider
here metric-affine gravity theories in which the gravitational action is a
general function of the scalar curvature while the matter action is allowed to
depend also on the connection which is not {\em a priori} symmetric. This
general treatment will allow us to address several open issues such as: the
relation between metric-affine gravity and General Relativity (in vacuum
as well as in the presence of matter), the implications of the dependence (or
independence) of the matter action on the connections, the origin and role of
torsion and the viability of the minimal-coupling principle.Comment: typos corrected, replaced to match published versio
Looking backward, looking forward: the city region of the mid-21st century
Emerging as a serious tool of analysis in the United States around 1950, the city region concept was increasingly applied in a European context after 1980. Since 2000, it has evolved further with recognition of the polycentric mega-city region, first recognised in Eastern Asia but now seen as an emerging urban form both in Europe and the United States. The paper speculates on the main changes that may impact on the growth and development of such complex urban regions in the first half of the 21st century, concluding that achieving the goal of polycentric urban development may prove more complex than at first it may seem
Taming the Runaway Problem of Inflationary Landscapes
A wide variety of vacua, and their cosmological realization, may provide an
explanation for the apparently anthropic choices of some parameters of particle
physics and cosmology. If the probability on various parameters is weighted by
volume, a flat potential for slow-roll inflation is also naturally understood,
since the flatter the potential the larger the volume of the sub-universe.
However, such inflationary landscapes have a serious problem, predicting an
environment that makes it exponentially hard for observers to exist and giving
an exponentially small probability for a moderate universe like ours. A general
solution to this problem is proposed, and is illustrated in the context of
inflaton decay and leptogenesis, leading to an upper bound on the reheating
temperature in our sub-universe. In a particular scenario of chaotic inflation
and non-thermal leptogenesis, predictions can be made for the size of CP
violating phases, the rate of neutrinoless double beta decay and, in the case
of theories with gauge-mediated weak scale supersymmetry, for the fundamental
scale of supersymmetry breaking.Comment: 31 pages, including 3 figure
Baryogenesis from Primordial Blackholes after Electroweak Phase Transition
Incorporating a realistic model for accretion of ultra-relativistic particles
by primordial blackholes (PBHs), we study the evolution of an Einstein-de
Sitter universe consisting of PBHs embedded in a thermal bath from the epoch
sec to sec. In this paper we use Barrow
et al's ansatz to model blackhole evaporation in which the modified Hawking
temperature goes to zero in the limit of the blackhole attaining a relic state
with mass . Both single mass PBH case as well as the case in which
blackhole masses are distributed in the range gm
have been considered in our analysis. Blackholes with mass larger than gm appear to survive beyond the electroweak phase transition and,
therefore, successfully manage to create baryon excess via
emissions, averting the baryon number wash-out due to sphalerons. In this
scenario, we find that the contribution to the baryon-to-entropy ratio by PBHs
of initial mass is given by , where
and are the CP-violating parameter and the initial mass
fraction of the PBHs, respectively. For larger than ,
the observed matter-antimatter asymmetry in the universe can be attributed to
the evaporation of PBHs.Comment: Latex2e file with seven figures included as postscript file
Royal and Lordly Residence in Scotland c 1050 to c 1250: an Historiographical Review and Critical Revision
Academic study of eleventh to thirteenth century high status residence in Scotland has been largely bypassed by the English debates over origin, function and symbolism. Archaeologists have also been slow to engage with three decades of historical revision of traditional socio-economic, cultural and political models upon which their interpretations of royal and lordly residence have drawn. Scottish castle-studies of the pre-1250 era continue to be framed by a ‘military architecture’ historiographical tradition and a view of the castle as an alien artefact imposed on the land by foreign adventurers and a ‘modernising’ monarchy and native Gaelic nobility. Knowledge and understanding of pre-twelfth century native high status sites is rudimentary and derived primarily from often inappropriate analogy with English examples. Discussion of native responses to the imported castle-building culture is founded upon retrospective projection of inappropriate later medieval social and economic models and anachronistic perceptions of military colonialism. Cultural and socio-economic difference is rarely recognised in archaeological modelling and cultural determinism has distorted perceptions of structural form, social status and material values. A programme of interdisciplinary studies focused on specific sites is necessary to provide a corrective to this current situation
Loop-Generated Bounds on Changes to the Graviton Dispersion Relation
We identify the effective theory appropriate to the propagation of massless
bulk fields in brane-world scenarios, to show that the dominant low-energy
effect of asymmetric warping in the bulk is to modify the dispersion relation
of the effective 4-dimensional modes. We show how such changes to the graviton
dispersion relation may be bounded through the effects they imply, through
loops, for the propagation of standard model particles. We compute these bounds
and show that they provide, in some cases, the strongest constraints on
nonstandard gravitational dispersions. The bounds obtained in this way are the
strongest for the fewest extra dimensions and when the extra-dimensional Planck
mass is the smallest. Although the best bounds come for warped 5-D scenarios,
for which the 5D Planck Mass is O(TeV), even in 4 dimensions the graviton loop
can lead to a bound on the graviton speed which is comparable with other
constraints.Comment: 18 pages, LaTeX, 4 figures, uses revte
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