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Mehmet Rauf'un Servet-i FĂŒnun'da tefrika edilen Ferda-yı Garam adlı roman
The singular behavior of massive QCD amplitudes
We discuss the structure of infrared singularities in on-shell QCD amplitudes
with massive partons and present a general factorization formula in the limit
of small parton masses. The factorization formula gives rise to an all-order
exponentiation of both, the soft poles in dimensional regularization and the
large collinear logarithms of the parton masses. Moreover, it provides a
universal relation between any on-shell amplitude with massive external partons
and its corresponding massless amplitude. For the form factor of a heavy quark
we present explicit results including the fixed-order expansion up to three
loops in the small mass limit. For general scattering processes we show how our
constructive method applies to the computation of all singularities as well as
the constant (mass-independent) terms of a generic massive n-parton QCD
amplitude up to the next-to-next-to-leading order corrections.Comment: version to appear in JHEP (sec. 3 with expanded discussion and
appendix with added results
Constraints on the gluon PDF from top quark pair production at hadron colliders
Using the recently derived NNLO cross sections \cite{Czakon:2013goa}, we
provide NNLO+NNLL theoretical predictions for top quark pair production based
on all the available NNLO PDF sets, and compare them with the most precise LHC
and Tevatron data. In this comparison we study in detail the PDF uncertainty
and the scale, and dependence of the theoretical predictions
for each PDF set. Next, we observe that top quark pair production provides a
powerful direct constraint on the gluon PDF at large , and include Tevatron
and LHC top pair data consistently into a global NNLO PDF fit. We then explore
the phenomenological consequences of the reduced gluon PDF uncertainties, by
showing how they can improve predictions for Beyond the Standard Model
processes at the LHC. Finally, we update to full NNLO+NNLL the theoretical
predictions for the ratio of top quark cross sections between different LHC
center of mass energies, as well as the cross sections for hypothetical heavy
fourth-generation quark production at the LHC.Comment: 29 pages, 13 figures, accepted for publication in JHE
Prospects for heavy supersymmetric charged Higgs boson searches at hadron colliders
We investigate the production of a heavy charged Higgs boson at hadron
colliders within the context of the MSSM. A detailed study is performed for all
important production modes and basic background processes for the
t\bar{t}b\bar{b} signature. In our analysis we include effects of initial and
final state showering, hadronization, and principal detector effects. For the
signal production rate we include the leading SUSY quantum effects at high
\tan\beta>~ mt/mb. Based on the obtained efficiencies for the signal and
background we estimate the discovery and exclusion mass limits of the charged
Higgs boson at high values of \tan\beta. At the upgraded Tevatron the discovery
of a heavy charged Higgs boson (MH^+ >~ 200 GeV) is impossible for the
tree-level cross-section values. However, if QCD and SUSY effects happen to
reinforce mutually, there are indeed regions of the MSSM parameter space which
could provide 3\sigma evidence and, at best, 5\sigma charged Higgs boson
discovery at the Tevatron for masses M_H^+<~ 300 GeV and M_H^+<~ 250 GeV,
respectively, even assuming squark and gluino masses in the (500-1000) GeV
range. On the other hand, at the LHC one can discover a H^+ as heavy as 1 TeV
at the canonical confidence level of 5\sigma; or else exclude its existence at
95% C.L. up to masses ~ 1.5 TeV. Again the presence of SUSY quantum effects can
be very important here as they may shift the LHC limits by a few hundred GeV.Comment: Latex2e, 44 pages, 15 figures, 6 tables, uses JHEP3.sty, axodraw.sty.
Comments added. Discussion on QCD factors clarified. Added discussion on
uncertainties. Change of presentation of Tables 4 and 5 and Fig.6. Results
and conclusions unchanged. Version accepted in JHE
PAMELA and FERMI-LAT limits on the neutralino-chargino mass degeneracy
Searches for Dark Matter (DM) particles with indirect detection techniques
have reached important milestones with the precise measurements of the
anti-proton and gamma-ray spectra, notably by the PAMELA and FERMI-LAT
experiments. While the gamma-ray results have been used to test the thermal
Dark Matter hypothesis and constrain the Dark Matter annihilation cross section
into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA
experiment remains relatively unexploited. Here we show that the latter can be
used to set a constraint on the neutralino-chargino mass difference. To
illustrate our point we use a Supersymmetric model in which the gauginos are
light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP)
is the neutralino. In this framework the W^+ W^- production is expected to be
significant, thus leading to large anti-proton and gamma-ray fluxes. After
determining a generic limit on the Dark Matter pair annihilation cross section
into W^+ W^- from the anti-proton data only, we show that one can constrain
scenarios in which the neutralino-chargino mass difference is as large as ~ 20
GeV for a mixed neutralino (and intermediate choices of the anti-proton
propagation scheme). This result is consistent with the limit obtained by using
the FERMI-LAT data. As a result, we can safely rule out the pure wino
neutralino hypothesis if it is lighter than 450 GeV and constitutes all the
Dark Matter.Comment: 22page
Updated Constraints on the Minimal Supergravity Model
Recently, refinements have been made on both the theoretical and experimental
determinations of the i.) mass of the lightest Higgs scalar (m_h), ii.) relic
density of cold dark matter in the universe (Omega_CDM h^2), iii.) branching
fraction for radiative B decay BF(b \to s \gamma), iv.) muon anomalous magnetic
moment (a_\mu), and v.) flavor violating decay B_s \to \mu^+\mu^-. Each of
these quantities can be predicted in the MSSM, and each depends in a
non-trivial way on the spectra of SUSY particles. In this paper, we present
updated constraints from each of these quantities on the minimal supergravity
(mSUGRA) model as embedded in the computer program ISAJET. The combination of
constraints points to certain favored regions of model parameter space where
collider and non-accelerator SUSY searches may be more focussed.Comment: 20 pages, 6 figures. Version published in JHE
pp -> ttH, H->tau tau: toward a model independent determination of the Higgs boson couplings at the LHC
The possibility of detecting a Higgs boson through several production and
decay channels is instrumental to the measurement of its couplings. In this
paper we study the pp-> ttH(H-> tau tau) channel at the LHC, for the case of a
scalar Higgs boson, and use the obtained results to improve on existing
strategies toward a model independent determination of the Higgs boson
couplings. The case of a scalar Higgs boson with mass below 140 GeV looks
particularly promising.Comment: 19 pages, 5 Figures, LaTex, published version, typos corrected,
comments added in Sec.
Direct, Indirect and Collider Detection of Neutralino Dark Matter In SUSY Models with Non-universal Higgs Masses
In supersymmetric models with gravity-mediated SUSY breaking, universality of
soft SUSY breaking sfermion masses m_0 is motivated by the need to suppress
unwanted flavor changing processes. The same motivation, however, does not
apply to soft breaking Higgs masses, which may in general have independent
masses from matter scalars at the GUT scale. We explore phenomenological
implications of both the one-parameter and two-parameter non-universal Higgs
mass models (NUHM1 and NUHM2), and examine the parameter ranges compatible with
Omega_CDM h^2, BF(b --> s,gamma) and (g-2)_mu constraints. In contrast to the
mSUGRA model, in both NUHM1 and NUHM2 models, the dark matter A-annihilation
funnel can be reached at low values of tan(beta), while the higgsino dark
matter annihilation regions can be reached for low values of m_0. We show that
there may be observable rates for indirect and direct detection of neutralino
cold dark matter in phenomenologically aceptable ranges of parameter space. We
also examine implications of the NUHM models for the Fermilab Tevatron, the
CERN LHC and a Sqrt(s)=0.5-1 TeV e+e- linear collider. Novel possibilities
include: very light s-top_R, s-charm_R squark and slepton_L masses as well as
light charginos and neutralinos and H, A and H^+/- Higgs bosons.Comment: LaTeX, 48pages, 26 Figures. The version with high resolution Figures
is available at http://hep.pa.msu.edu/belyaev/public/projects/nuhm/nuhm.p
Linear Collider Capabilities for Supersymmetry in Dark Matter Allowed Regions of the mSUGRA Model
Recent comparisons of minimal supergravity (mSUGRA) model predictions with
WMAP measurements of the neutralino relic density point to preferred regions of
model parameter space. We investigate the reach of linear colliders (LC) with
and 1 TeV for SUSY in the framework of the mSUGRA model. We find
that LCs can cover the entire stau co-annihilation region provided \tan\beta
\alt 30. In the hyperbolic branch/focus point (HB/FP) region of parameter
space, specialized cuts are suggested to increase the reach in this important
``dark matter allowed'' area. In the case of the HB/FP region, the reach of a
LC extends well past the reach of the CERN LHC. We examine a case study in the
HB/FP region, and show that the MSSM parameters and can be
sufficiently well-measured to demonstrate that one would indeed be in the HB/FP
region, where the lightest chargino and neutralino have a substantial higgsino
component.Comment: 29 pages, 15 EPS figures; updated version slightly modified to
conform with published versio
Measurement of B meson production cross-sections in proton-proton collisions at âs= 7 TeV
The production cross-sections of B mesons are measured in pp collisions at a centre-of-mass energy of 7 TeV using data collected with the LHCb detector corresponding to a integrated luminosity of 0.36fbâ1. The B+, B0 and B0s mesons are reconstructed in the exclusive decays B+âJ/ÏK+, B0âJ/ÏKâ0 and B0sâJ/ÏÏ, with J/ÏâÎŒ+ÎŒâ, Kâ0âK+Ïâ and ÏâK+Kâ. The differential cross-sections are measured as functions of B meson transverse momentum pT and rapidity y, in the range 0 < pT<40GeV/c2 and 2.0<y<4.5. The integrated cross-sections in the same pT and y ranges, including charge-conjugate states, are measured to be
Ï(ppâB++X)=38.9±0.3(stat.)±2.5(syst.)±1.3(norm.)ÎŒb,
Ï(ppâB0+X)=38.1±0.6(stat.)±3.7(syst.)±4.7(norm.)ÎŒb,
Ï(ppâB0s+X)=10.5±0.2(stat.)±0.8(syst.)±1.0(norm.)ÎŒb,
where the third uncertainty arises from the pre-existing branching fraction measurements
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