1,214 research outputs found
The Jeffreys-Lindley Paradox and Discovery Criteria in High Energy Physics
The Jeffreys-Lindley paradox displays how the use of a p-value (or number of
standard deviations z) in a frequentist hypothesis test can lead to an
inference that is radically different from that of a Bayesian hypothesis test
in the form advocated by Harold Jeffreys in the 1930s and common today. The
setting is the test of a well-specified null hypothesis (such as the Standard
Model of elementary particle physics, possibly with "nuisance parameters")
versus a composite alternative (such as the Standard Model plus a new force of
nature of unknown strength). The p-value, as well as the ratio of the
likelihood under the null hypothesis to the maximized likelihood under the
alternative, can strongly disfavor the null hypothesis, while the Bayesian
posterior probability for the null hypothesis can be arbitrarily large. The
academic statistics literature contains many impassioned comments on this
paradox, yet there is no consensus either on its relevance to scientific
communication or on its correct resolution. The paradox is quite relevant to
frontier research in high energy physics. This paper is an attempt to explain
the situation to both physicists and statisticians, in the hope that further
progress can be made.Comment: v4: Continued editing for clarity. Figure added. v5: Minor fixes to
biblio. Same as published version except for minor copy-edits, Synthese
(2014). v6: fix typos, and restore garbled sentence at beginning of Sec 4 to
v
Constraining Supersymmetry using the relic density and the Higgs boson
Recent measurements by Planck, LHC experiments, and Xenon100 have significant
impact on supersymmetric models and their parameters. We first illustrate the
constraints in the mSUGRA plane and then perform a detailed analysis of the
general MSSM with 13 free parameters. Using SFitter, Bayesian and Profile
Likelihood approaches are applied and their results compared. The allowed
structures in the parameter spaces are largely defined by different mechanisms
of dark matter annihilation in combination with the light Higgs mass
prediction. In mSUGRA the pseudoscalar Higgs funnel and stau co-annihilation
processes are still avoiding experimental pressure. In the MSSM stau
co-annihilation, the light Higgs funnel, a mixed bino--higgsino region
including the heavy Higgs funnel, and a large higgsino region predict the
correct relic density. Volume effects and changes in the model parameters
impact the extracted mSUGRA and MSSM parameter regions in the Bayesian
analysis
Long lived charginos in Natural SUSY?
Supersymmetric models with a small neutralino-chargino mass difference, and
as a result metastable charginos, have been a popular topic of investigation in
collider phenomenology, e.g. in anomaly-mediated models of supersymmetry
breaking. Recently, the absence of any supersymmetric signal at the 8 TeV LHC
data has led to significant interest in the so-called Natural SUSY models with
light higgsinos. These models also have a naturally small neutralino-chargino
mass difference. However, we show here that when relevant indirect constraints
from results at the LHC and elsewhere are applied, this possibility is heavily
constrained within the Minimal Supersymmetric Standard Model (MSSM): massive
metastable higgsinos are not a signature of Natural SUSY.Comment: Extended discussion, updated references, matches version to appear in
JHE
On the detectability of the CMSSM light Higgs boson at the Tevatron
We examine the prospects of detecting the light Higgs h^0 of the Constrained
MSSM at the Tevatron. To this end we explore the CMSSM parameter space with
\mu>0, using a Markov Chain Monte Carlo technique, and apply all relevant
collider and cosmological constraints including their uncertainties, as well as
those of the Standard Model parameters. Taking 50 GeV < m_{1/2}, m_0 < 4 TeV,
|A_0| < 7 TeV and 2 < tan(beta) < 62 as flat priors and using the formalism of
Bayesian statistics we find that the 68% posterior probability region for the
h^0 mass lies between 115.4 GeV and 120.4 GeV. Otherwise, h^0 is very similar
to the Standard Model Higgs boson. Nevertheless, we point out some enhancements
in its couplings to bottom and tau pairs, ranging from a few per cent in most
of the CMSSM parameter space, up to several per cent in the favored region of
tan(beta)\sim 50 and the pseudoscalar Higgs mass of m_A\lsim 1 TeV. We also
find that the other Higgs bosons are typically heavier, although not
necessarily much heavier. For values of the h^0 mass within the 95% probability
range as determined by our analysis, a 95% CL exclusion limit can be set with
about 2/fb of integrated luminosity per experiment, or else with 4/fb (12/fb) a
3 sigma evidence (5 sigma discovery) will be guaranteed. We also emphasize that
the alternative statistical measure of the mean quality-of-fit favors a
somewhat lower Higgs mass range; this implies even more optimistic prospects
for the CMSSM light Higgs search than the more conservative Bayesian approach.
In conclusion, for the above CMSSM parameter ranges, especially m_0, either
some evidence will be found at the Tevatron for the light Higgs boson or, at a
high confidence level, the CMSSM will be ruled out.Comment: JHEP versio
Direct Constraints on Minimal Supersymmetry from Fermi-LAT Observations of the Dwarf Galaxy Segue 1
The dwarf galaxy Segue 1 is one of the most promising targets for the
indirect detection of dark matter. Here we examine what constraints 9 months of
Fermi-LAT gamma-ray observations of Segue 1 place upon the Constrained Minimal
Supersymmetric Standard Model (CMSSM), with the lightest neutralino as the dark
matter particle. We use nested sampling to explore the CMSSM parameter space,
simultaneously fitting other relevant constraints from accelerator bounds, the
relic density, electroweak precision observables, the anomalous magnetic moment
of the muon and B-physics. We include spectral and spatial fits to the Fermi
observations, a full treatment of the instrumental response and its related
uncertainty, and detailed background models. We also perform an extrapolation
to 5 years of observations, assuming no signal is observed from Segue 1 in that
time. Results marginally disfavour models with low neutralino masses and high
annihilation cross-sections. Virtually all of these models are however already
disfavoured by existing experimental or relic density constraints.Comment: 22 pages, 5 figures; added extra scans with extreme halo parameters,
expanded introduction and discussion in response to referee's comment
Constraints on Extended Neutral Gauge Structures
Indirect precision data are used to constrain the masses of possible extra
Z^prime bosons and their mixings with the ordinary Z. We study a variety of
Z^prime bosons as they appear in E_6 and left-right unification models, the
sequential Z boson, and the example of an additional U(1) in a concrete model
from heterotic string theory. In all cases the mixings are severely constrained
(sin theta < 0.01). The lower mass limits are generally of the order of several
hundred GeV and competitive with collider bounds. The exception is the Z_psi
boson, whose vector couplings vanish and whose limits are weaker. The results
change little when the rho parameter is allowed, which corresponds to a
completely arbitrary Higgs sector. On the other hand, in specific models with
minimal Higgs structures the limits are generally pushed into the TeV region.Comment: 13 pages of LaTeX2e, 6 figure
Dark matter protohalos in MSSM-9 and implications for direct and indirect detection
We study how the kinetic decoupling of dark matter (DM) within a minimal
supersymmetric extension of the standard model, by adopting nine independent
parameters (MSSM-9), could improve our knowledge of the properties of the DM
protohalos. We show that the most probable neutralino mass regions, which
satisfy the relic density and the Higgs mass contraints, are those with the
lightest supersymmetric neutralino mass around 1 TeV and 3 TeV, corresponding
to Higgsino-like and Wino-like neutralino, respectively. The kinetic decoupling
temperature in the MSSM-9 scenario leads to a most probable protohalo mass in a
range of . The part of the
region closer to 2 TeV gives also important contributions from the
neutralino-stau co-annihilation, reducing the effective annihilation rate in
the early Universe. We also study how the size of the smallest DM substructures
correlates to experimental signatures, such as the spin-dependent and
spin-independent scattering cross sections, relevant for direct detection of
DM. Improvements on the spin-independent sensitivity might reduce the most
probable range of the protohalo mass between 10 and
10, while the expected spin-dependent sensitivity
provides weaker constraints. We show how the boost of the luminosity due to DM
annihilation increases, depending on the protohalo mass. In the Higgsino case,
the protohalo mass is lower than the canonical value often used in the
literature (10), while does not
deviate from cm s; there is no
significant enhancement of the luminosity. On the contrary, in the Wino case,
the protohalo mass is even lighter, and is two orders
of magnitude larger; as its consequence, we see a substantial enhancement of
the luminosity.Comment: 26 pages, 8 figure
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