Pseudoscalar Masses Research Articles

Search for Neutral Minimal Supersymmetric Standard Model Higgs Bosons Decaying to Tau Pairs inppCollisions ats=7 TeV

A search for neutral MSSM Higgs bosons in pp collisions at the LHC at a center-of-mass energy of 7 TeV is presented. The results are based on a data sample corresponding to an integrated luminosity of 36 inverse picobarns recorded by the CMS experiment. The search uses decays of the Higgs bosons to tau pairs. No excess is observed in the tau-pair invariant-mass spectrum. The resulting upper limits on the Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, yield stringent new bounds in the MSSM parameter space.

Lopsided gauge mediation

It has been recently pointed out that the unavoidable tuning among supersymmetric parameters required to raise the Higgs boson mass beyond its experimental limit opens up new avenues for dealing with the so called $\mu$-$B_\mu$ problem of gauge mediation. In fact, it allows for accommodating, with no further parameter tuning, large values of $B_\mu$ and of the other Higgs-sector soft masses, as predicted in models where both $\mu$ and $B_\mu$ are generated at one-loop order. This class of models, called Lopsided Gauge Mediation, offers an interesting alternative to conventional gauge mediation and is characterized by a strikingly different phenomenology, with light higgsinos, very large Higgs pseudoscalar mass, and moderately light sleptons. We discuss general parametric relations involving the fine-tuning of the model and various observables such as the chargino mass and the value of $\tan\beta$. We build an explicit model and we study the constraints coming from LEP and Tevatron. We show that in spite of new interactions between the Higgs and the messenger superfields, the theory can remain perturbative up to very large scales, thus retaining gauge coupling unification.

Finite fermion mass effects in pseudoscalar Higgs production via gluon–gluon fusion

We compute the leading logarithmic behaviour of the cross-section for the production of a pseudoscalar Higgs boson in gluon–gluon fusion to all-orders in perturbation theory, in the limit of large partonic centre of mass energy. We also calculate the Higgs rapidity distribution to the same accuracy. We include the contributions of top and bottom quarks, together with their interference. Our results are given in terms of single and double integrals, evaluated explicitly up to next-to next-to leading order (NNLO). We use our results to improve the known NNLO inclusive cross-section computed in the effective theory where the fermions in the loop are integrated out. The size of finite fermion mass effects on the inclusive cross-section is found to be small, reaching a few percent only for large values of the pseudoscalar mass.

Meson screening masses from lattice QCD with two light quarks and one strange quark

We present results for screening masses of mesons built from light and strange quarks in the temperature range of approximately between 140 MeV to 800 MeV. The lattice computations were performed with 2+1 dynamical light and strange flavors of improved (p4) staggered fermions along a line of constant physics defined by a pion mass of about 220 MeV and a kaon mass of 500 MeV. The lattices had temporal extents Nt = 4, 6 and 8 and aspect ratios of Ns / Nt \geq 4. At least up to a temperature of 140 MeV the pseudo-scalar screening mass remains almost equal to the corresponding zero temperature pseudo-scalar (pole) mass. At temperatures around 3Tc (Tc being the transition temperature) the continuum extrapolated pseudo-scalar screening mass approaches very close to the free continuum result of 2 \pi T from below. On the other hand, at high temperatures the vector screening mass turns out to be larger than the free continuum value of 2 \pi T. The pseudo-scalar and the vector screening masses do not become degenerate even for a temperature as high as 4Tc. Using these mesonic spatial correlation functions we have also investigated the restoration of chiral symmetry and the effective restoration of the axial symmetry. We have found that the vector and the axial-vector screening correlators become degenerate, indicating chiral symmetry restoration, at a temperature which is consistent with the QCD transition temperature obtained in previous studies. On the other hand, the pseudo-scalar and the scalar screening correlators become degenerate only at temperatures larger than 1.3Tc, indicating that the effective restoration of the axial symmetry takes place at a temperature larger than the QCD transition temperature.

Pseudoscalar mass spectrum in a soft-wall model of AdS/QCD

The anti--de Sitter space/conformal field theory (AdS/CFT) correspondence may offer new and useful insights into the nonperturbative regime of strongly coupled gauge theories such as quantum chromodynamics (QCD). Recently, a modified soft-wall AdS/QCD model incorporated independent sources for explicit and spontaneous chiral symmetry breaking and linear confinement. This model contains a modified dilaton and higher-order interaction terms in the Lagrangian. Within this model we explore the radial pseudoscalar mass spectrum using two different representations of the pion field. We find the mass eigenvalues associated with each representation show the equivalence between the two, and we find good agreement with the pion masses. The Gell-Mann--Oakes--Renner (GOR) relation is naturally obtained.

Chiral dynamics with strange quarks in the light of recent lattice simulations

Several lattice collaborations performing simulations with 2+1 light dynamical quarks have experienced difficulties in fitting their data with standard N f = 3 chiral expansions at next-to-leading order, yielding low values of the quark condensate and/ or the decay constant in the N f = 3 chiral limit. A reordering of these expansions seems required to analyse these data in a consistent way. We discuss such a reordering, known as Resummed Chiral Perturbation Theory, in the case of pseudoscalar masses and decay constants, pion and kaon electromagnetic form factors and K ℓ3 form factors. We show that it provides a good fit of the recent results of two lattice collaborations (PACS-CS and RBC/UKQCD). We describe the emerging picture for the pattern of chiral symmetry breaking, marked by a strong dependence of the observables on the strange quark mass and thus a significant difference between chiral symmetry breaking in the N f = 2 and N f =3 chiral limits. We discuss the consequences for the ratio of decay constants F K /F π and the K ℓ3 form factor at vanishing momentum transfer.

Light meson physics from maximally twisted mass lattice QCD

We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for N f = 2 mass-degenerate quark flavours. By employing four values of the lattice spacing, spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 ≲ m PS ≲ 650MeV we control the major systematic effects of our calculation. This enables us to confront our N f = 2 data with SU(2) chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass.

Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks

We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (N_f = 2+1+1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a~0.078 fm and a~0.086 fm with lattice sizes ranging from L~1.9 fm to L~2.8 fm. We measure with high statistical precision the light pseudoscalar mass m_PS and decay constant f_PS in a range 270 < m_PS < 510 MeV and determine the low energy parameters f_0, l_3 and l_4 of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to N_f=2 results are performed.

Higgs-induced flavor-changing neutral current as a source of new physics inb→stransitions

The experimental study of $B$ mesons suggest the existence of some new physics contribution to the ${B}_{s}^{0}\ensuremath{-}{\overline{B}}_{s}^{0}$ mixing. We study the implications of a hypothesis that this contribution is generated by the Higgs-induced flavor-changing neutral currents (FCNC). We concentrate on the specific $b\ensuremath{\rightarrow}s$ transition which is described by two complex FCNC parameters, ${F}_{23}$ and ${F}_{32}$, and parameters in the Higgs sector. Model-independent constraints on these parameters are derived from the ${B}_{s}^{0}\ensuremath{-}{\overline{B}}_{s}^{0}$ mixing and are used to predict the branching ratios for ${\overline{B}}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and ${\overline{B}}_{d}\ensuremath{\rightarrow}\overline{K}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ numerically by considering general variations in the Higgs parameters assuming that Higgs sector conserves $CP$. Taking the results on ${B}_{s}^{0}\ensuremath{-}{\overline{B}}_{s}^{0}$ mixing derived by the global analysis of UTfit group as a guide we present the general constraints on ${F}_{23}^{*}{F}_{32}$ in terms of the pseudoscalar mass ${M}_{A}$. The former is required to be in the range $\ensuremath{\sim}(1--5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}{M}_{A}^{2}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}2}$ if the Higgs-induced FCNC represent the dominant source of new physics. The phases of these couplings can account for the large $CP$ violating phase in the ${B}_{s}^{0}\ensuremath{-}{\overline{B}}_{s}^{0}$ mixing except when ${F}_{23}={F}_{32}$. The Higgs contribution to ${\overline{B}}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ branching ratio can be large, close to the present limit while it remains close to the standard model value in case of the process ${\overline{B}}_{d}\ensuremath{\rightarrow}\overline{K}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ for all the models under study. We identify and discuss various specific examples which can naturally lead to suppressed FCNC in the ${K}^{0}\ensuremath{-}{\overline{K}}^{0}$ mixing allowing at the same time the required values for ${F}_{23}^{*}$ and ${F}_{32}$.

RADIATIVE CORRECTIONS IN VECTOR-TENSOR MODELS

We consider a two-form antisymmetric tensor field ϕ minimally coupled to a non-Abelian vector field with a field strength F. Canonical analysis suggests that a pseudoscalar mass term [Formula: see text] for the tensor field eliminates degrees of freedom associated with this field. Explicit one-loop calculations show that an additional coupling m Tr (ϕ ∧ F) (which can be eliminated classically by a tensor field shift) reintroduces tensor field degrees of freedom. We attribute this to the lack of the renormalizability in our vector-tensor model. We also explore a vector-tensor model with a tensor field scalar mass term [Formula: see text] and coupling m Tr (ϕ ∧ ⋆F). We comment on the Stueckelberg mechanism for mass generation in the Abelian version of the latter model.

Low-lying baryon spectrum with two dynamical twisted mass fermions

The masses of the low-lying baryons are evaluated using two degenerate flavors of twisted mass sea quarks corresponding to pseudoscalar masses in the range of about 270\char21{}500 MeV. The strange valence quark mass is tuned to reproduce the mass of the kaon in the physical limit. The tree-level Symanzik improved gauge action is employed. We use lattices of spatial size 2.1 and 2.7 fm at two values of the lattice spacing with ${r}_{0}/a=5.22(2)$ and ${r}_{0}/a=6.61(3)$. We check for both finite volume and cutoff effects on the baryon masses. We performed a detailed study of the chiral extrapolation of the octet and decuplet masses using SU(2) $\ensuremath{\chi}\mathrm{PT}$. The lattice spacings determined using the nucleon mass at the physical point are consistent with the values extracted using the pion decay constant. We examine the issue of isospin symmetry breaking for the octet and decuplet baryons and its dependence on the lattice spacing. We show that in the continuum limit isospin breaking is consistent with zero, as expected. The baryon masses that we find after taking the continuum limit and extrapolating to the physical limit are in good agreement with experiment.

Magnetic equation of state in (2+1)-flavor QCD

A first study of critical behavior in the vicinity of the chiral phase transition of (2+1)-flavor QCD is presented. We analyze the quark mass and volume dependence of the chiral condensate and chiral susceptibilities in QCD with two degenerate light quark masses and a strange quark. The strange quark mass (m_s) is chosen close to its physical value; the two degenerate light quark masses (m_l) are varied in a wide range 1/80 \le m_l/m_s \le 2/5, where the smallest light quark mass value corresponds to a pseudo-scalar Goldstone mass of about 75 MeV. All calculations are performed with staggered fermions on lattices with temporal extent Nt=4. We show that numerical results are consistent with O(N) scaling in the chiral limit. We find that in the region of physical light quark mass values, m_l/m_s \simeq 1/20, the temperature and quark mass dependence of the chiral condensate is already dominated by universal properties of QCD that are encoded in the scaling function for the chiral order parameter, the magnetic equation of state. We also provide evidence for the influence of thermal fluctuations of Goldstone modes on the chiral condensate at finite temperature. At temperatures below, but close to the chiral phase transition at vanishing quark mass, this leads to a characteristic dependence of the light quark chiral condensate on the square root of the light quark mass.

Correlation between direct dark matter detection andBr(Bs→μμ)with a large phase ofBs−B¯smixing

We combine the analyses for flavor changing neutral current processes and dark matter solutions in minimal-type supersymmetric grand unified theory models, SO(10) and SU(5), with a large B s -B s mixing phase and large tanβ. For large tanβ, the double-penguin diagram dominates the supersymmetry contribution to the B s -B s mixing amplitude. Also, the Br(B s → μμ) constraint becomes important as it grows as tan 6 β, although it can still be suppressed by a large pseudoscalar Higgs mass m A . We investigate the correlation between B s → μμ and the dark matter direct detection cross section through their dependence on m A . In the minimal-type of SU(5) with type I seesaw, the large mixing in neutrino Dirac couplings results in a large lepton flavor violating decay process τ → μγ, which in turn sets the upper bound on m A . In the SO(10) case, the large mixing can be chosen to be in the Majorana couplings instead, and the constraint from Br(τ → μγ) can be avoided. The heavy Higgs funnel region turns out to be an interesting possibility in both cases and the direct dark matter detection should be possible in the near future in these scenarios.

Update on the direct detection of dark matter in MSSM models with non-universal Higgs masses

We discuss the possibilities for the direct detection of neutralino dark matter via elastic scattering in variants of the minimal supersymmetric extension of the Standard Model (MSSM) with non-universal supersymmetry-breaking contributions to the Higgs masses, which may be either equal (NUHM1) or independent (NUHM2). We compare the ranges found in the NUHM1 and NUHM2 with that found in the MSSM with universal supersymmetry-breaking contributions to all scalar masses, the CMSSM. We find that both the NUHM1 and NUHM2 offer the possibility of larger spin-independent dark matter scattering cross sections than in the CMSSM for larger neutralino masses, since they allow the density of heavier neutralinos with large Higgsino components to fall within the allowed range by astrophysics. The NUHM1 and NUHM2 also offer more possibilities than the CMSSM for small cross sections for lower neutralino masses, since they may be suppressed by scalar and pseudoscalar Higgs masses that are larger than in the CMSSM.

On the radiative corrections to the neutral Higgs boson masses in the NMSSM

We provide a full one-loop calculation of the self energies and tadpoles of the neutral Higgs bosons of the NMSSM. In addition, we compute the two-loop O ( α t α s + α b α s ) corrections to the neutral Higgs boson masses in the effective potential approximation. With respect to earlier calculations, the newly-computed corrections can account for shifts of a few GeV in the light scalar and pseudoscalar masses, and they can also sizeably affect the mixing between singlet and MSSM-like Higgs scalars. Taking these corrections into account will be crucial for a meaningful comparison between the MSSM and NMSSM predictions for the Higgs sector.

PAMELA excess from neutralino annihilation in the NMSSM

We examine whether the cosmic ray positron excess observed by PAMELA can be explained by neutralino annihilation in the next-to-minimal supersymmetric standard model (NMSSM). The main dark matter annihilation products are the lightest $CP$-even scalar ${h}_{1}$ plus the lightest $CP$-odd scalar ${a}_{1}$, with the ${a}_{1}$ decaying into two muons. The energetic positrons needed to explain PAMELA are thus obtained in the NMSSM simply from kinematics. The required large annihilation cross section is obtained from an $s$-channel resonance with the heavier $CP$-odd scalar ${a}_{2}$. Various experiments constrain the PAMELA-favored NMSSM parameter space, including collider searches for a light ${a}_{1}$. These constraints point to a unique corner of the NMSSM parameter space, having a lightest neutralino mass around 160 GeV and a very light pseudoscalar mass less than a GeV. A simple parametrized formula for the charge-dependent solar modulation effects reconciles the discrepancy between the PAMELA data and the estimated background at lower energies. We also discuss the electron and gamma-ray spectra from the Fermi LAT observations, and point out the discrepancy between the NMSSM predictions and Fermi LAT preliminary results and possible resolution. An NMSSM explanation of PAMELA makes three striking and uniquely correlated predictions: the rise in the PAMELA positron spectrum will turn over at around 70 GeV, the dark matter particle mass is less than the top quark mass, and a light sub-GeV pseudoscalar will be discovered at colliders.

SCALAR AND PSEUDOSCALAR GLUEBALLS

We employ two simple and robust results to constrain the mixing matrix of the isosinglet scalar mesons f0(1710), f0(1500), f0(1370): one is the approximate SU (3) symmetry empirically observed in the scalar sector above 1 GeV and confirmed by lattice QCD, and the other is the scalar glueball mass at 1710 MeV in the quenched approximation. In the SU (3) symmetry limit, f0(1500) becomes a pure SU (3) octet and is degenerate with a0(1450), while f0(1370) is mainly an SU (3) singlet with a slight mixing with the scalar glueball which is the primary component of f0(1710). These features remain essentially unchanged even when SU (3) breaking is taken into account. The observed enhancement of ωf0(1710) production over ɸf0(1710) in hadronic J/ψ decays and the copious f0(1710) production in radiative J/ψ decays lend further support to the prominent glueball nature of f0(1710). We deduce the mass of the pseudoscalar glueball G from an η-η′-G mixing formalism based on the anomalous Ward identity for transition matrix elements. With the inputs from the recent KLOE experiment, we find a solution for the pseudoscalar glueball mass around (1.4±0.1) GeV, which is fairly insensitive to a range of inputs with or without Okubo-Zweig-Iizuka-rule violating effects. This affirms that η(1405), having a large production rate in the radiative J/ψ decay and not seen in γγ reactions, is indeed a leading candidate for the pseudoscalar glueball. It is much lower than the results from quenched lattice QCD (&gt; 2.0 GeV) due to the dynamic fermion effect. It is thus urgent to have a full QCD lattice calculation of pseudoscalar glueball masses.

Penguin contribution to the phase of [formula omitted]–[formula omitted] mixing and [formula omitted] in grand unified theories

We investigate the possibility of a large Bs–Bs¯ mixing phase in the context of grand unified theory (GUT) models, e.g., SO(10) and SU(5). In these models, we find that a large phase of Bs mixing is correlated with Br(b→sγ), Br(τ→μγ) and Br(Bs→μμ) for large tanβ. In the case of the SO(10) model, the large phase of Bs mixing is correlated with Br(b→sγ) and Br(Bs→μμ) and we find that a large Bs mixing corresponds to an enhanced Br(Bs→μμ) about to be probed by the Tevatron. In the case of the SU(5) model, the large phase is correlated with Br(τ→μγ) and Br(Bs→μμ). In this case, the Br(τ→μγ) constraint requires a smaller pseudo-scalar Higgs mass which in turn generates a large Br(Bs→μμ) almost at the edge of present experimental constraint. If the present observation of large phase of Bs mixing persists in the upcoming data, using all these branching ratios, we will be able to distinguish these models.

Implications of the Higgs discovery in the MSSM golden region

If the lightest CP-even Higgs boson in the MSSM is discovered at the LHC, two measurements could be made simultaneously: the Higgs mass m_h and the event rate Bs(gg -> h -> gamma gamma). We study to what extent the combination of these two measurements would allow us to extract parameters in the stop mass matrix, including the off-diagonal mixing term, with a focus on the MSSM golden region where the stops are light and the mixing is large. Even though both the production cross-section and the decay amplitude are not sensitive to supersymmetric parameters outside of the stop sector, the branching ratio depends on the total decay width, which is dominated by the Higgs decay to b quarks and sensitive to both the pseudo-scalar mass m_A and the supersymmetric Higgs mass \mu. In the end we find m_A is an important input in extracting the stop mass parameters, while a fair estimate of the off-diagonal mixing term could be obtained without prior knowledge of \mu.

Screening of light mesons and charmonia at high temperature

We present lattice QCD results for the screening masses of light mesons and charmonia. The lattice computations were performed with 2 + 1 flavors of improved staggered quarks using quark masses which correspond to realistic pion and kaon masses at zero temperature. For the light quark sector we have found that the screening masses in the pseudo-scalar and the isovector scalar channels do not become degenerate at the chiral crossover temperature indicating an effective non-restoration of the axial symmetry. Also the splitting between the vector and the pseudo-scalar screening masses persists even in the limit of zero lattice spacing and at a moderately high temperature around 420 MeV. In the charmonium sector our investigation shows that the screening masses of the pseudo-scalar and the vector charmonia are almost (within a few percent) equal to their zero temperature masses for temperatures less than 300 MeV. We also present results for the charmonium screening masses using periodic boundary conditions along the temporal direction and discuss their implications.