179,627 research outputs found
An exploration of hadronic interactions in blazars using IceCube
Context: Hadronic models, involving matter (proton or nuclei) acceleration in
blazar jets, imply high energy photon and neutrino emissions due to
interactions of high-energy protons with matter and/or radiation in the source
environment. Aims: This paper shows that the sensitivity of the IceCube
neutrino telescope in its 40-string configuration (IC-40) is already at the
level of constraining the parameter space of purely hadronic scenarios of
activity of blazars. Methods: Assuming that the entire source power originates
from hadronic interactions, and assuming that the models describe the data, we
estimate the expected neutrino flux from blazars based on the observed
gamma-ray flux by Fermi, simultaneously with IC-40 observations. We consider
two cases separately to keep the number of constrainable parameters at an
acceptable level: proton-proton or proton-gamma interactions are dominant.
Comparing the IC-40 sensitivity to the neutrino flux expected from some of the
brightest blazars, we constrain model parameters characterizing the parent
high-energy proton spectrum. Results: We find that when pp interactions
dominate, some constraints on the primary proton spectrum can be imposed. For
instance, for the tightest constrained source 3C 454.3, the very high energy
part of the spectra of blazars is constrained to be harder than E^-2 with
cut-off energies in the range of Ecut >10^18 eV. When interactions of
high-energy protons on soft photon fields dominate, we can find similarly tight
constraints on the proton spectrum parameters. [abridged]Comment: accepted for publication in A&
Discovering New Light States at Neutrino Experiments
Experiments designed to measure neutrino oscillations also provide major
opportunities for discovering very weakly coupled states. In order to produce
neutrinos, experiments such as LSND collide thousands of Coulombs of protons
into fixed targets, while MINOS and MiniBooNE also focus and then dump beams of
muons. The neutrino detectors beyond these beam dumps are therefore an
excellent arena in which to look for long-lived pseudoscalars or for vector
bosons that kinetically mix with the photon. We show that these experiments
have significant sensitivity beyond previous beam dumps, and are able to
partially close the gap between laboratory experiments and supernovae
constraints on pseudoscalars. Future upgrades to the NuMI beamline and Project
X will lead to even greater opportunities for discovery. We also discuss thin
target experiments with muon beams, such as those available in COMPASS, and
show that they constitute a powerful probe for leptophilic PNGBs.Comment: 32 text pages, 5 figures, 4 table
Hunting for Dark Matter Coannihilation by Mixing Dijet Resonances and Missing Transverse Energy
Simplified models of the dark matter (co)annihilation mechanism predict
striking new collider signatures untested by current searches. These models,
which were codified in the coannihilation codex, provide the basis for a dark
matter (DM) discovery program at the Large Hadron Collider (LHC) driven by the
measured DM relic density. In this work, we study an exemplary model featuring
-channel DM coannihilation through a scalar diquark mediator as a
representative case study of scenarios with strongly interacting coannihilation
partners. We discuss the full phenomenology of the model, ranging from low
energy flavor constraints, vacuum stability requirements, and precision Higgs
effects to direct detection and indirect detection prospects. Moreover,
motivated by the relic density calculation, we find significant portions of
parameter space are compatible with current collider constraints and can be
probed by future searches, including a proposed analysis for the novel
signature of a dijet resonance accompanied by missing transverse energy (MET).
Our results show that the TeV LHC with luminosity
should be sensitive to mediators as heavy as 1 TeV and dark matter in the
400--500 GeV range. The combination of searches for single and paired dijet
peaks, non-resonant jets + MET excesses, and our novel resonant dijet + MET
signature have strong coverage of the motivated relic density region,
reflecting the tight connections between particles determining the dark matter
abundance and their experimental signatures at the LHC.Comment: 35 pages, 9 figure
Constraining the neutron-matter equation of state with gravitational waves
We show how observations of gravitational waves from binary neutron star
(BNS) mergers over the next few years can be combined with insights from
nuclear physics to obtain useful constraints on the equation of state (EoS) of
dense matter, in particular, constraining the neutron-matter EoS to within 20%
between one and two times the nuclear saturation density $n_0\approx 0.16\
{\text{fm}^{-3}}$. Using Fisher information methods, we combine observational
constraints from simulated BNS merger events drawn from various population
models with independent measurements of the neutron star radii expected from
x-ray astronomy (the Neutron Star Interior Composition Explorer (NICER)
observations in particular) to directly constrain nuclear physics parameters.
To parameterize the nuclear EoS, we use a different approach, expanding from
pure nuclear matter rather than from symmetric nuclear matter to make use of
recent quantum Monte Carlo (QMC) calculations. This method eschews the need to
invoke the so-called parabolic approximation to extrapolate from symmetric
nuclear matter, allowing us to directly constrain the neutron-matter EoS. Using
a principal component analysis, we identify the combination of parameters most
tightly constrained by observational data. We discuss sensitivity to various
effects such as different component masses through population-model
sensitivity, phase transitions in the core EoS, and large deviations from the
central parameter values.Comment: 13 pages, 9 figures + supplement 11 page
The Minimal SUSY Model: From the Unification Scale to the LHC
This paper introduces a random statistical scan over the high-energy initial
parameter space of the minimal SUSY model--denoted as the MSSM.
Each initial set of points is renormalization group evolved to the electroweak
scale--being subjected, sequentially, to the requirement of radiative and
electroweak symmetry breaking, the present experimental lower bounds on the
vector boson and sparticle masses, as well as the lightest neutral Higgs
mass of 125 GeV. The subspace of initial parameters that satisfies all
such constraints is presented, shown to be robust and to contain a wide range
of different configurations of soft supersymmetry breaking masses. The
low-energy predictions of each such "valid" point - such as the sparticle mass
spectrum and, in particular, the LSP - are computed and then statistically
analyzed over the full subspace of valid points. Finally, the amount of
fine-tuning required is quantified and compared to the MSSM computed using an
identical random scan. The MSSM is shown to generically require less
fine-tuning.Comment: 65 pages, 18 figure
SUSY-Breaking Parameters from RG Invariants at the LHC
We study Renormalization Group invariant (RGI) quantities in the Minimal
Supersymmetric Standard Model and show that they are a powerful and simple
instrument for testing high scale models of supersymmetry (SUSY)-breaking. For
illustration, we analyze the frameworks of minimal and general gauge mediated
(MGM and GGM) SUSY-breaking, with additional arbitrary soft Higgs mass
parameters at the messenger scale. We show that if a gaugino and two first
generation sfermion soft masses are determined at the LHC, the RGIs lead to MGM
sum rules that yield accurate predictions for the other gaugino and first
generation soft masses. RGIs can also be used to reconstruct the fundamental
MGM parameters (including the messenger scale), calculate the hypercharge
D-term, and find relationships among the third generation and Higgs soft
masses. We then study the extent to which measurements of the full first
generation spectrum at the LHC may distinguish different SUSY-breaking
scenarios. In the case of MGM, although most deviations violate the sum rules
by more than estimated experimental errors, we find a 1-parameter family of GGM
models that satisfy the constraints and produce the same first generation
spectrum. The GGM-MGM degeneracy is lifted by differences in the third
generation masses and the messenger scales.Comment: (v1) 30 pages; (v2) mislabeling in figs 2 and 3 corrected, version
accepted for publication in Phys. Rev.
Electric dipole moments as probes of new physics
We review several aspects of flavour-diagonal CP violation, focussing on the
role played by the electric dipole moments (EDMs) of leptons, nucleons, atoms
and molecules, which consitute the source of several stringent constraints on
new CP-violating physics. We dwell specifically on the calculational aspects of
applying the hadronic EDM constraints, reviewing in detail the application of
QCD sum-rules to the calculation of nucleon EDMs and CP-odd pion-nucleon
couplings. We also consider the current status of EDMs in the Standard Model,
and on the ensuing constraints on the underlying sources of CP-violation in
physics beyond the Standard Model, focussing on weak-scale supersymmetry.Comment: 62 pages, 10 figures, invited review to appear in Annals of Physics;
v2: references adde
Neutralino Proton Cross Sections In Supergravity Models
The neutralino-proton cross section is examined for supergravity models with
R-parity invariance with universal and non-universal soft breaking. The region
of parameter space that dark matter detectors are currently (or will be
shortly) sensitive i.e. pb, is examined. For universal
soft breaking (mSUGRA), detectors with sensitivity
pb will be able to
sample parts of the parameter space for .
Current relic density bounds restrict GeV
for the maximum cross sections, which is below where astronomical uncertainties
about the Milky Way are relevant. Nonuniversal soft breaking models can allow
much larger cross sections and can sample the parameter space for . In such models, can be quite large reducing the
tension between proton decay bounds and dark matter analysis. We note the
existance of two new domains where coannihilation effects can enter, i.e. for
mSUGRA at large , and for nonuniversal models with small .Comment: 22 pages, latex, 18 figure
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