54 research outputs found
Flavour physics constraints in the BMSSM
We study the implications of the presence of the two leading-order,
non-renormalizable operators in the Higgs sector of the MSSM to flavour physics
observables. We identify the constraints of flavour physics on the parameters
of the BMSSM when we: a) focus on a region of parameters for which electroweak
baryogenesis is feasible, b) use a CMSSM-like parametrization, and c) consider
the case of a generic NUHM-type model. We find significant differences as
compared to the standard MSSM case.Comment: 22 pages, 7 figure
The decay Bs -> mu+ mu-: updated SUSY constraints and prospects
We perform a study of the impact of the recently released limits on BR(Bs ->
mu+ mu-) by LHCb and CMS on several SUSY models. We show that the obtained
constraints can be superior to those which are derived from direct searches for
SUSY particles in some scenarios, and the use of a double ratio of purely
leptonic decays involving Bs -> mu+ mu- can further strengthen such
constraints. We also discuss the experimental sensitivity and prospects for
observation of Bs -> mu+ mu- during the sqrt(s)=7 TeV run of the LHC, and its
potential implications.Comment: 30 pages, 21 figures. v2: Improved discussion of constraints from B
-> tau nu, references adde
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at = 2.76 TeV
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb
collisions at TeV at the Large Hadron Collider is
presented. We observe a growing trend with energy now not only for the
longitudinal and the outward but also for the sideward pion source radius. The
pion homogeneity volume and the decoupling time are significantly larger than
those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/388
Supersymmetric Monojets at the Large Hadron Collider
Supersymmetric monojets may be produced at the Large Hadron Collider by the
process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a
jet recoiling against missing transverse momentum. We discuss the feasibility
and utility of the supersymmetric monojet signal. In particular, we examine the
possible precision with which one can ascertain the neutralino_1-squark-quark
coupling via the rate for monojet events. Such a coupling contains information
on the composition of the neutralino_1 and helps bound dark matter direct
detection cross-sections and the dark matter relic density of the neutralino_1.
It also provides a check of the supersymmetric relation between gauge couplings
and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an
error that appears in all previous versions of the appendix. This error has
no effect on the results in the main body of the pape
Flavor Physics in an SO(10) Grand Unified Model
In supersymmetric grand-unified models, the lepton mixing matrix can possibly
affect flavor-changing transitions in the quark sector. We present a detailed
analysis of a model proposed by Chang, Masiero and Murayama, in which the
near-maximal atmospheric neutrino mixing angle governs large new b -> s
transitions. Relating the supersymmetric low-energy parameters to seven new
parameters of this SO(10) GUT model, we perform a correlated study of several
flavor-changing neutral current (FCNC) processes. We find the current bound on
B(tau -> mu gamma) more constraining than B(B -> X_s gamma). The LEP limit on
the lightest Higgs boson mass implies an important lower bound on tan beta,
which in turn limits the size of the new FCNC transitions. Remarkably, the
combined analysis does not rule out large effects in B_s-B_s-bar mixing and we
can easily accomodate the large CP phase in the B_s-B_s-bar system which has
recently been inferred from a global analysis of CDF and DO data. The model
predicts a particle spectrum which is different from the popular Constrained
Minimal Supersymmetric Standard Model (CMSSM). B(tau -> mu gamma) enforces
heavy masses, typically above 1 TeV, for the sfermions of the degenerate first
two generations. However, the ratio of the third-generation and
first-generation sfermion masses is smaller than in the CMSSM and a (dominantly
right-handed) stop with mass below 500 GeV is possible.Comment: 44 pages, 5 figures. Footnote and references added, minor changes,
Fig. 2 corrected; journal versio
Impact of LHC Searches on NLSP Top Squark and Gluino Mass
We explore the implications of 7 TeV LHC searches for a scenario in which one
of the stops is the next-to lightest supersymmetric particle (NLSP). The NLSP
stop (\tilde{t}_1) is assumed to decay exclusively into neutralino and charm
quark. We consider processes where the stops are pair produced together with a
hard QCD jet. We also consider stop quarks from gluino decays, \tilde{g}\to
t\tilde{t}_1^\ast+\bar{t}\tilde{t}_1. We show that the monojet ATLAS and CMS
searches corresponding to 1 fb^{-1} of integrated luminosity are sensitive to
stop masses of up to 160 GeV, with the 20% neutralino-stop coannihilation
region essentially ruled out for M_{\tilde{t}_1}\lesssim 140 GeV. The region
M_{\tilde{t}_1}\lesssim 130 GeV is excluded with even relatively larger mass
difference, M_{\tilde{t}_1}-M_{\tilde{\chi}_1^0}\sim 40 GeV, by the multi-jets
search. The b-jet and same-sign dilepton searches are sensitive to a heavier
gluino because they only pick up gluino pair production events followed by top
quarks decaying into b-jets and same-sign dileptons, respectively. We find that
the LHC data places a lower limit on the gluino mass in this scenario of about
600 GeV (700 GeV) from b-jets (same-sign dileptons) searches.Comment: 18 pages, 10 figures and 4 table
Naturalness of the Non-Universal MSSM in the light of the recent Higgs results
We analyse the naturalness of the Minimal Supersymmetric Standard Model
(MSSM) in the light of recent LHC results from the ATLAS and CMS experiments.
We study non-universal boundary conditions for the scalar and the gaugino
sector, with fixed relations between some of the soft breaking parameters, and
find a significant reduction of fine-tuning for non-universal gaugino masses.
For a Higgs mass of about 125 GeV, as observed recently, we find parameter
regions with a fine-tuning of O(10), taking into account experimental and
theoretical uncertainties. These regions also survive after comparison with
simplified model searches in ATLAS and CMS. For a fine-tuning less than 20 the
lightest neutralino is expected to be lighter than about 400 GeV and the
lighter stop can be as heavy as 3.5 TeV. On the other hand, the gluino mass is
required to be above 1.5 TeV. For non-universal gaugino masses, we discuss
which fixed GUT scale ratios can lead to a reduced fine-tuning and find that
the recent Higgs results have a strong impact on which ratio is favoured. We
also discuss the naturalness of GUT scale Yukawa relations, comparing the
non-universal MSSM with the CMSSM.Comment: 24 pages, 8 figures; version accepted for publication in JHE
A 119-125 GeV Higgs from a string derived slice of the CMSSM
The recent experimental hints for a relatively heavy Higgs with a mass in the range 119-125 GeV favour supersymmetric scenarios with a large mixing in the stop mass matrix. It has been shown that this is possible in the constrained Minimal Super-symmetric Standard Model (CMSSM), but only for a very specific relation between the trilinear parameter and the soft scalar mass, favouring A ≈ −2m for a relatively light spectrum, and sizable values of tan β. We describe here a string-derived scheme in which the first condition is automatic and the second arises as a consequence of imposing radiative EW symmetry breaking and viable neutralino dark matter in agreement with WMAP constraints. More specifically, we consider modulus dominated SUSY-breaking in Type II string compactifications and show that it leads to a very predictive CMSSM-like scheme, with small departures due to background fluxes. Imposing the above constraints leaves only one free parameter, which corresponds to an overall scale. We show that in this construction A=−3/2–√m≃−2mA=−3/2m≃−2m and in the allowed parameter space tan β ≃ 38 − 41, leading to 119 GeV < mh < 125 GeV. The recent LHCb results on BR(Bs → μ+μ−) further constrain this range, leaving only the region with mh ~ 125. GeV. We determine the detectability of this model and show that it could start being probed by the LHC at 7(8) TeV with a luminosity of 5(2) fb−1, and the whole parameter space would be accessible for 14 TeV and 25 fb−1. Furthermore, this scenario can host a long-lived stau with the right properties to lead to catalyzed BBN. We finally argue that anthropic arguments could favour the highest value for the Higgs mass that is compatible with neutralino dark matter, i.e., mh-125 GeV
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe
- …