201 research outputs found
Interplay of Direct and Indirect Searches for New Physics
We report recent work on the interplay of collider and flavour physics
regarding the search for physics beyond the Standard Model.Comment: 4 pages, based on an invited talk at PANIC11, MIT, Cambridge, USA,
24.-29.7.201
Status of Higgs couplings after Run-1 of the LHC using Lilith 1.0
We provide an update of the global fits of the couplings of the 125.5 GeV
Higgs boson using all publicly available experimental results from Run-1 of the
LHC as per Summer 2014. The fits are done by means of the new public code
Lilith 1.0. We present a selection of results given in terms of signal
strengths, reduced couplings, and for the Two-Higgs-Doublet Models of Type I
and II.Comment: 12 pages, 4 figure
Diagnosing Degenerate Higgs Bosons at 125 GeV
We develop diagnostic tools that would provide incontrovertible evidence for
the presence of more than one Higgs boson near 125 GeV in the LHC data.Comment: 4 pages, 2 figure
The phenomenological MSSM in view of the 125 GeV Higgs data
The parameter space of the phenomenological MSSM (pMSSM) is explored by means
of Markov Chain Monte Charlo (MCMC) methods, taking into account the latest LHC
results on the Higgs signal at 125 GeV in addition to relevant low-energy
observables and LEP constraints. We use a Bayesian approach to derive posterior
densities for the parameters and observables of interests. We find in
particular that the Higgs measurements have a significant impact on the
parameters mu and tan beta due to radiative corrections to the bottom Yukawa
coupling. We show moreover the impact of the most recent dark matter
measurements on the probability distributions, and we discuss prospects for the
next run of the LHC at 13-14 TeV.Comment: 28 pages, 13 figures; v2: matches version accepted for publication in
PR
Thermal leptogenesis and the gravitino problem in the Asaka-Yanagida axion/axino dark matter scenario
A successful implementation of thermal leptogenesis requires the re-heat
temperature after inflation T_R to exceed ~2\times 10^9 GeV. Such a high T_R
value typically leads to an overproduction of gravitinos in the early universe,
which will cause conflicts, mainly with BBN constraints. Asaka and Yanagida
(AY) have proposed that these two issues can be reconciled in the context of
the Peccei-Quinn augmented MSSM (PQMSSM) if one adopts a mass hierarchy
m(sparticle)>m(gravitino)>m(axino), with m(axino) keV. We calculate the relic
abundance of mixed axion/axino dark matter in the AY scenario, and investigate
under what conditions a value of T_R sufficient for thermal leptogenesis can be
generated. A high value of PQ breaking scale f_a is needed to suppress
overproduction of axinos, while a small vacuum misalignment angle \theta_i is
needed to suppress overproduction of axions. The large value of f_a results in
late decaying neutralinos. To avoid BBN constraints, the AY scenario requires a
low thermal abundance of neutralinos and high values of neutralino mass. We
include entropy production from late decaying saxions, and find the saxion
needs to be typically at least several times heavier than the gravitino. A
viable AY scenario suggests that LHC should discover a spectrum of SUSY
particles consistent with weak scale supergravity; that the apparent neutralino
abundance is low; that a possible axion detection signal (probably with m_axion
in the sub-micro-eV range) should occur, but no direct or indirect signals for
WIMP dark matter should be observed.Comment: 28 pages including 21 .eps figures; high resolution pdf version
available at http://www.nhn.ou.edu/~bae
Reconciling thermal leptogenesis with the gravitino problem in SUSY models with mixed axion/axino dark matter
Successful implementation of thermal leptogenesis requires re-heat
temperatures T_R\agt 2\times 10^9 GeV, in apparent conflict with SUSY models
with TeV-scale gravitinos, which require much lower T_R in order to avoid Big
Bang Nucleosynthesis (BBN) constraints. We show that mixed axion/axino dark
matter can reconcile thermal leptogenesis with the gravitino problem in models
with m_{\tG}\agt 30 TeV, a rather high Peccei-Quinn breaking scale and an
initial mis-alignment angle \theta_i < 1. We calculate axion and axino dark
matter production from four sources, and impose BBN constraints on long-lived
gravitinos and neutralinos. Moreover, we discuss several SUSY models which
naturally have gravitino masses of the order of tens of TeV. We find a
reconciliation difficult in Yukawa-unified SUSY and in AMSB with a wino-like
lightest neutralino. However, T_R\sim 10^{10}-10^{12} GeV can easily be
achieved in effective SUSY and in models based on mixed moduli-anomaly
mediation. Consequences of this scenario include: 1. an LHC SUSY discovery
should be consistent with SUSY models with a large gravitino mass, 2. an
apparent neutralino relic abundance \Omega_{\tz_1}h^2\alt 1, 3. no WIMP direct
or indirect detection signals should be found, and 4. the axion mass should be
less than \sim 10^{-6} eV, somewhat below the conventional range which is
explored by microwave cavity axion detection experiments.Comment: 25 pages including 15 .eps figures; updated version to coincide with
published versio
Prospects for Yukawa Unified SO(10) SUSY GUTs at the CERN LHC
The requirement of t-b-\tau Yukawa coupling unification is common in simple
grand unified models based on the gauge group SO(10), and it also places a
severe constraint on the expected spectrum of superpartners. For Yukawa-unified
models with \mu >0, the spectrum is characterized by three mass scales: {\it
i}). first and second generation scalars in the multi-TeV range, {\it ii}).
third generation scalars, \mu and m_A in the few-TeV range and {\it iii}).
gluinos in the \sim 350-500 GeV range with chargino masses around 100-160 GeV.
In such a scenario, gluino pair production should occur at large rates at the
CERN LHC, followed by gluino three-body decays into neutralinos or charginos.
Discovery of Yukawa-unified SUSY at the LHC should hence be possible with only
1 fb^{-1} of integrated luminosity, by tagging multi-jet events with 2--3
isolated leptons, without relying on missing E_T. A characteristic dilepton
mass edge should easily be apparent above Standard Model background. Combining
dileptons with b-jets, along with the gluino pair production cross section
information, should allow for gluino and neutralino mass reconstruction. A
secondary corroborative signal should be visible at higher integrated
luminosity in the W1Z2-> 3\ell channel, and should exhibit the same dilepton
mass edge as in the gluino cascade decay signal.Comment: 25 pages including 18 EPS figure
The Flavour of Natural SUSY
An inverted mass hierarchy in the squark sector, as in so-called "natural
supersymmetry", requires non-universal boundary conditions at the mediation
scale of supersymmetry breaking. We propose a formalism to define such boundary
conditions in a basis-independent manner and apply it to generic scenarios
where the third-generation squarks are light, while the first two generation
squarks are heavy and near-degenerate. We show that not only is our formalism
particularly well-suited to study such hierarchical squark mass patterns, but
in addition the resulting soft terms at the TeV scale are manifestly compatible
with the principle of minimal flavour violation, and thus automatically obey
constraints from flavour physics.Comment: 19 pages, 4 figures; v2: matches journal versio
Constraints on and future prospects for Two-Higgs-Doublet Models in light of the LHC Higgs signal
We analyze the Two-Higgs-Doublet Models (2HDMs) of Type I and II for
consistency with the latest measurements of the ~125.5 GeV Higgs-like signal at
the LHC. To this end, we perform scans of the 2HDM parameter space taking into
account all relevant pre-LHC constraints as well as the most recent limits
coming from searches for heavy Higgs-like states at the LHC. The current status
of the 2HDMs of Type I and II is discussed assuming that the observed 125.5 GeV
state is one of the two CP-even Higgs bosons, either the lighter h or the
heavier H. Implications for future experiments, including expectations
regarding other lighter or heavier Higgs bosons are given. The possible
importance of heavier Higgs bosons feeding the signals for the 125.5 GeV state
is also evaluated.Comment: 52 pages, 32 figures, match to the published versio
Electroweak Phase Transition and LHC Signatures in the Singlet Majoron Model
We reconsider the strength of the electroweak phase transition in the singlet
Majoron extension of the Standard Model, with a low (~TeV) scale of the singlet
VEV. A strongly first order phase transition, of interest for electroweak
baryogenesis, is found in sizeable regions of the parameter space, especially
when the cross-coupling lambda_{hs}|S|^2|H|^2 between the singlet and the
doublet Higgs is significant. Large Majorana Yukawa couplings of the singlet
neutrinos, y_i S nu_i^c nu_i, are also important for strengthening the
transition. We incorporate the LEP and Tevatron constraints on the Higgs
masses, and electroweak precision constraints, in our search for allowed
parameters; successful examples include singlet masses ranging from 5 GeV to
several TeV. Models with a strong phase transition typically predict a
nonstandard Higgs with mass in the range 113 GeV < m_H < 200 GeV and production
cross sections reduced by mixing with the singlet, with cos^2(theta)
significantly less than 1. We also find examples where the singlet is light and
the decay H -> SS can modify the Higgs branching ratios relative to Standard
Model expectations.Comment: 36 pages, 18 figure
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