arXiv subjects

Vernon Barger

Publications and source records attributed to Vernon Barger.

At least 181 records · Page 10Linked to original sources

arXiv2011

Proton size anomaly

A measurement of the Lamb shift in muonic hydrogen yields a charge radius of the proton that is smaller than the CODATA value by about 5 standard deviations. We explore the possibility that new scalar, pseudoscalar, vector, and tensor flavor-conserving nonuniversal interactions may be responsible for the discrepancy. We consider exotic particles that among leptons, couple preferentially to muons, and mediate an attractive nucleon-muon interaction. We find that the many constraints from low energy data disfavor new spin-0, spin-1 and spin-2 particles as an explanation.

hep-ph↗

arXiv2011

Tevatron Asymmetry of Tops in a W',Z' Model

Recent results from the CDF Collaboration indicate the the top-pair forward-backward asymmetry is largest in regions of high rapidity difference $|Δy|$ and invariant mass $M_{t\bar t}.$ We show that experimental observations can be explained by our previously proposed Asymmetric Left-Right Model (ALRM). The gauge symmetry $U'(1)\times SU'(2)\times SU(2)$ is broken by a triplet Higgs in the primed sector. The $W'$ boson has a $(t,d)$ right-handed coupling and the $Z'$ boson has diagonal fermion couplings. We determine the model parameters to be $M_{W'} = 700$ GeV, $M_{Z'}=1$ TeV, and charged current coupling $g'_2=3$. The $W'$ and $Z'$ total decay widths are of $\mathcal{O}(100$ GeV). The signals from $Z'\to t\bar t$ and $W'\to tb$ at the LHC will test the model.

hep-ph↗

arXiv2011

Hollow cone sieve for top

A method of top tagging is introduced. Using the anti-kt algorithm to define jets, events with nj = 2 fat jets of cone size R = 1.5 are decomposed into R = 0.6 sub-jets and retained if nj (R= 0.6) >= 4 . One pair of sub-jets reconstructs the W-mass and another jet is tagged as a b-jet, as necessary for hadronic or semileptonic events of tt origin. This 'hollow cone' method distinguishes the tt events from the light parton QCD dijet events.

hep-ph↗

arXiv2010

Electromagnetic properties of dark matter: dipole moments and charge form factor

A neutral dark matter particle may possess an electric dipole moment (EDM) or a magnetic dipole moment (MDM), so that its scattering with nuclei is governed by electromagnetic interactions. If the moments are associated with relevant operators of dimension-5, they may be detectable in direct search experiments. We calculate complete expressions of the scattering cross sections and the recoil energy spectra for dark matter with these attributes. We also provide useful formulae pertinent to dark matter that interacts via an electric charge form factor (CFF) which is related to the charge radius defined by an effective dimension-6 operator. We show that a 7 GeV dark matter particle with an EDM, MDM or CFF easily reproduces the CoGeNT excess while remaining consistent with null searches.

hep-ph↗

arXiv2010

Triple-Top Signal of New Physics at the LHC

We present leading-order (LO) cross sections for the production of three top quarks ($tt\tb$,$t\tb\tb$) at the Large Hadron Collider (LHC). We find a total LO cross section for triple-top production in the Standard Model of $σ\approx 2 $ fb at $\sqrt{s}=14$ TeV and we give examples of two new physics models which have a significant enhancement to this channel. In the Minimal Supersymmetric Standard Model (MSSM), there are regions of parameter space where the decays of gluino pairs into final states including three tops has a cross section $σ\approx 41$ fb. In a leptophobic $Z'$ model featuring right-handed couplings of the $u$-quark to the top, we find $σ\approx 28$ fb. With efficient identification and reconstruction of the top quarks, the triple-top signal could potentially provide evidence for new physics at the LHC.

hep-ph↗

arXiv2010

Three Layers of Neutrinos

In this letter we point out that in a class of models for spontaneous R-parity breaking based on gauged B-L, the spectrum for neutrinos is quite peculiar. We find that those models generally predict three layers of neutrinos: one heavy sterile neutrino, two massive active neutrinos, and three near massless (one active and two sterile) neutrinos.

hep-ph↗

arXiv2010

Complex Scalar Dark Matter vis-à-vis CoGeNT, DAMA/LIBRA and XENON100

The CoGeNT and DAMA/LIBRA experiments have found evidence for the spin-independent scattering from nuclei of a light dark matter (DM) particle, 7-12 GeV, which is not excluded by the XENON DM experiments. We show that this putative DM signal can be explained by a complex scalar singlet extension of the standard model (CSM), with a thermal cosmological DM density, and a Higgs sector that is consistent with LEP constraints. We make predictions for the masses, production, and decays of the two Higgs mass eigenstates and describe how the Higgs and DM particles can be discovered at the LHC.

hep-ph↗

arXiv2010

Light Higgs Boson, Light Dark Matter and Gamma Rays

A light Higgs boson is preferred by $M_W$ and $m_t$ measurements. A complex scalar singlet addition to the Standard Model allows a better fit to these measurements through a new light singlet dominated state. It then predicts a light Dark Matter (DM) particle that can explain the signals of DM scattering from nuclei in the CoGeNT and DAMA/LIBRA experiments. Annihilations of this DM in the galactic halo, $AA\rightarrow b\bar{b}, c\bar{c}, τ^+τ^-$, lead to gamma rays that naturally improve a fit to the Fermi Large Area Telescope data in the central galactic regions. The associated light neutral Higgs boson may also be discovered at the Large Hadron Collider.

hep-ph↗

arXiv2010

Fermion WIMPless Dark Matter at DeepCore and IceCube

We investigate the prospects for indirect detection of fermion WIMPless dark matter at the neutrino telescopes IceCube and DeepCore. The dark matter annihilating in the Sun is a hidden sector Majorana fermion that couples through Yukawa couplings to a connector particle and a visible sector particle, and it exhibits only spin-dependent scattering with nuclei via couplings to first generation quarks. We consider cases where the annihilation products are taus, staus, or sneutrinos of the three generations. To evaluate the muon fluxes incident at the detector, we propagate the neutrino spectra through the solar medium and to the Earth and account for the effects of neutrino oscillations, energy losses due to neutral- and charged-current interactions, and tau regeneration. We find that for the stau and sneutrino channels, a 5 yr 3$σ$ detection of dark matter lighter than about 300 GeV is possible at IceCube for large Yukawa couplings or for dark matter and connector particles with similar masses. The tau channel offers far better detection prospects. However, due to its lower energy threshold and better muon background rejection capability, DeepCore is able to detect signals in all annihilation channels and for a wider range of dark matter masses.

hep-ph↗

arXiv2010

Asymmetric Left-Right Model and the Top Pair Forward-Backward Asymmetry

The forward-backward asymmetry measurement in top-pair production at the Tevatron is about $2σ$ from the Standard Model prediction. We propose an asymmetric left-right model, which includes a $W'$ boson with a right-handed coupling of down to top quark, and a $Z'$ boson with diagonal couplings to the up, top, and down quarks with $M_{W'}\approx175$ GeV and $M_{Z'}\approx 900$ GeV. The model accounts for the asymmetry while remaining consistent with the top-pair total cross-section and invariant mass distribution.

hep-ph↗

arXiv2010

Capability of LHC to discover supersymmetry with \sqrt{s}=7 TeV and 1 fb^{-1}

We examine the capability of the CERN Large Hadron Collider to discovery supersymmetry (SUSY) with energy \sqrt{s}=7 TeV and integrated luminosity of about 1 fb^{-1}. Our results are presented within the paradigm minimal supergravity model (mSUGRA or CMSSM). Using a 6-dimensional grid of cuts for optimization of signal to background-- including missing E_T-- we find for m_{\tg}\sim m_{\tq} an LHC reach of m_{\tg}\sim 800,\ 950,\ 1100 and 1200 GeV for 0.1, 0.3, 1 and 2 fb^{-1}, respectively. For m_{\tg}<< m_{\tq}, the reach is instead near m_{\tg}\sim 480,\ 540,\ 620 and 700 GeV, for the same integrated luminosities. We also examine the LHC reach in the case of very low integrated luminosity where missing E_T may not be viable. We focus on the multi-muon, multi-lepton (including electrons) and dijet signals. Although the LHC reach without E_T^{miss} is considerably lower in these cases, it is still substantial: for 0.3 fb^{-1}, the dijet reach in terms of gluino mass is up to 600 GeV for very low m_0, while the dilepton reach is to gluino masses of \sim 500 GeV over a range of m_0 values.

hep-ph↗

arXiv2009

Six-Lepton Z' Resonance at the Large Hadron Collider

New physics models admit the interesting possibility of a Z' weak boson associated with an extra U(1) gauge symmetry and a Higgs boson that is heavy enough to decay into a pair of Z bosons. Then Z' production and decay via Z' -> ZH -> ZZZ has a distinctive LHC signal that is nearly background free and reconstructs the H and Z' masses and widths. The Z' decay to 3 pairs of leptons is especially distinctive. The ZH decay mode exists even if the Z' is decoupled from leptons, which motivates an independent 6-lepton resonance search regardless of the dilepton search results.

hep-ph↗

arXiv2009

Single top and Higgs associated production at the LHC

We study the production of a Standard Model (SM) Higgs boson in association with a single top quark and either a light jet or $W$-boson at the LHC with a center of mass energy of 14 TeV. Due to the destructive interference of the contributing SM diagrams, the value of the top Yukawa coupling and the sign of the $WWh$ coupling may be probed for Higgs masses above 150 GeV where $WW$ and $ZZ$ are the dominant Higgs decays. We consider Higgs masses of $m_{h}=120$, 150, 180, and 200 GeV and devise experimental cuts to extract the signal from SM backgrounds and measure the top Yukawa coupling.

hep-ph↗

arXiv2009

SUSY dark matter and lepton flavor violation

We study lepton flavor-violating (LFV) processes within a supersymmetric type-I seesaw framework with flavor-blind universal boundary conditions, properly accounting for the effect of the neutrino sector on the dark matter relic abundance. We consider several possibilities for the neutrino Yukawa coupling matrix and show that in regions of SUSY parameter space that yield the correct neutralino relic density, LFV rates can differ from naive estimates by up to two orders of magnitude. Contrary to common belief, we find that current LFV limits do not exclude neutrino Yukawa couplings larger than top Yukawa couplings. We introduce the ISAJET-M program that was used for the computations.

hep-ph↗

arXiv2009

$b \to s$ Transitions in Family-dependent $U(1)^\prime$ Models

We analyze flavor-changing-neutral-current (FCNC) effects in the $b\to s$ transitions that are induced by family non-universal $U(1)'$ gauge symmetries. After systematically developing the necessary formalism, we present a correlated analysis for the $ΔB =1, 2$ processes. We adopt a model-independent approach in which we only require family-universal charges for the first and second generations and small fermion mixing angles. We analyze the constraints on the resulting parameter space from $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (π, ϕ, η', ρ, ω, f_0)K_S$ decays. Our results indicate that the currently observed discrepancies in some of these modes with respect to the Standard Model predictions can be consistently accommodated within this general class of models.

hep-ph↗

arXiv2009

Higgs ID at the LHC

We make a complete catalog of extended Higgs sectors involving SU(2)_L doublets and singlets, subject to natural flavor conservation. In each case we present the couplings of a light neutral CP-even Higgs state h in terms of the model parameters, and identify which models are distinguishable in principle based on this information. We also give explicit expressions for the model parameters in terms of h couplings and exhibit the behaviors of the couplings in the limit where the deviations from the Standard Model Higgs couplings are small. Finally we discuss prospects for differentiation of extended Higgs models based on measurements at the LHC and ILC and identify the regions in which these experiments could detect deviations from the SM Higgs predictions.

hep-ph↗

arXiv2009

Family Non-universal $U(1)^\prime$ Gauge Symmetries and $b\to s$ Transitions

We present a correlated analysis for the $ΔB =1, 2$ processes which occur via $b\to s$ transitions within models with a family non-universal $U(1)^\prime$. We take a model-independent approach, and only require family universal charges for the first and second generations and small fermion mixing angles. The results of our analysis show that within this class of models, the anomalies in $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (π, ϕ, η', ρ, ω, f_0)K_S$ decays can be accommodated.

hep-ph↗

arXiv2009

Minimal gauged U(1)_{B-L} model with spontaneous R-parity violation

We study the minimal gauged U(1)_{B-L} supersymmetric model and show that it provides an attractive theory for spontaneous R-parity violation. Both U(1)_{B-L} and R-parity are broken by the vacuum expectation value of the right-handed sneutrino (proportional to the soft SUSY masses), thereby linking the B-L and soft SUSY scales. In this context we find a consistent mechanism for generating neutrino masses and a realistic mass spectrum, all without extending the Higgs sector of the minimal supersymmetry standard model. We discuss the most relevant collider signals and the connection between the Z' gauge boson and R-parity violation.

hep-ph↗