arXiv subjects

Aneesh V. Manohar

Publications and source records attributed to Aneesh V. Manohar.

At least 55 records · Page 3Linked to original sources

arXiv2013

Naive Dimensional Analysis Counting of Gauge Theory Amplitudes and Anomalous Dimensions

We show that naive dimensional analysis (NDA) is equivalent to the result that L-loop scattering amplitudes have perturbative order N=L+Delta, with a shift Delta that depends on the NDA-weight of operator insertions. The NDA weight of an operator is defined in this paper, and the general NDA formula for perturbative order N is derived. The formula is used to explain why the one-loop anomalous dimension matrix for dimension-six operators in the Standard Model effective field theory has entries with perturbative order ranging from 0 to 4. The results in this paper are valid for an arbitrary effective field theory, and they constrain the coupling constant dependence of anomalous dimensions and scattering amplitudes in a general effective field theory.

hep-ph↗

arXiv2013

The Topology and Size of the Universe from CMB Temperature and Polarization Data

We analyze seven year and nine year WMAP temperature maps for signatures of three finite flat topologies M_0=T^3, M_1=T^2 x R^1, and M_2=S^1 x R^2. We use Monte-Carlo simulations with the Feldman-Cousins method to obtain confidence intervals for the size of the topologies considered. We analyze the V, W, and Q frequency bands along with the ILC map and find no significant difference in the results. The 95.5% confidence level lower bound on the size of the topology is 1.5L_0 for M_0, 1.4L_0 for M_1, and 1.1L_0 for M_2, where L_0 is the radius of the last scattering surface. Our results agree very well with the recently released results from the Planck temperature data. We show that the likelihood function is not Gaussian in the size, and therefore simulations are important for obtaining accurate bounds on the size. We then introduce the formalism for including polarization data in the analysis. The improvement that we find from WMAP polarization maps is small because of the high level of instrumental noise, but our forecast for Planck maps shows a much better improvement on the lower bound for L. For the M_0 topology we expect an improvement on the lower bound of L from 1.7L_0 to 1.9L_0 at 95.5% confidence level. Using both polarization and temperature data is important because it tests the hypothesis that deviations in the TT spectrum at small l originate in the primordial perturbation spectrum.

astro-ph.CO↗

arXiv2013

An Exactly Solvable Model for Dimension Six Higgs Operators and $h \to γγ$

An exactly solvable large $N$ model is constructed which reduces at low energies to the Standard Model plus the dimension six Higgs-gauge operators $g_1^2 H^\dagger H B_{μν} B^{μν}$, $g_2^2 H^\dagger H W^a_{μν} W^{aμν}$, $g_1 g_2 H^\dagger τ^a H W^a_{μν} B^{μν}$, and $ε^{abc} W^a_μ{}^νW^b_ν{}^ρW^c_ρ{}^μ$. All other dimension six operators are suppressed by powers of $1/N$. The Higgs-gauge operators lead to deviations from the Standard Model $h \to γγ$ and $h \to γZ$ rates. A simple variant of the model can be used to also generate the Higgs-gluon operator $g_3^2 H^\dagger H G^A_{μν} G^{Aμν}$ which contributes to the Higgs production rate via gluon fusion.

hep-ph↗

arXiv2013

Limits on Semiclassical Fluctuations in the Primordial Universe

We place limits on semiclassical fluctuations that might be present in the primordial perturbation spectrum. These can arise if some signatures of pre-inflationary features survive the expansion, or could be created by whatever mechanism ends inflation. We study two possible models for such remnant fluctuations, both of which break the isotropy of CMB on large scales. We first consider a semiclassical fluctuation in one Fourier mode of primordial perturbations. The second scenario we analyze is a semiclassical Gaussian bump somewhere in space. These models are tested with the seven-year WMAP data using a Markov Chain Monte Carlo Bayesian analysis, and we place limits on these fluctuations. The upper bound for the amplitude of a fluctuation in a single Fourier mode is a<=10^(-4), while for the Gaussian bump a<=10^(-3).

astro-ph.CO↗

arXiv2013

Double Parton Correlations in the Bag Model

Double parton scattering is sensitive to correlations between the two partons in the hadron, including correlations in flavor, spin, color, momentum fractions and transverse separation. We obtain a first estimate of the size of these correlations by calculating the corresponding double parton distribution functions in a bag model of the proton. We find significant correlations between momentum fractions, spin and flavor, but negligible correlations with transverse separation. The model estimates of the relative importance of these correlations will help experimental studies disentangle them.

hep-ph↗

arXiv2013

Renormalization Group Scaling of Higgs Operators and Γ(h -> γγ)

We compute the renormalization of dimension six Higgs-gauge boson operators that can modify Γ(h -> γγ) at tree-level. Operator mixing is shown to lead to an important modification of new physics effects which has been neglected in past calculations. We also find that the usual formula for the S oblique parameter contribution of these Higgs-gauge boson operators needs additional terms to be consistent with renormalization group evolution. We study the implications of our results for Higgs phenomenology and for new physics models which attempt to explain a deviation in Γ(h -> γγ). We derive a new relation between the S parameter and the Γ(h -> γγ) and Γ(h ->Z γ) decay rates.

hep-ph↗

arXiv2012

What is Double Parton Scattering?

Processes such as double Drell-Yan and same-sign WW production have contributions from double parton scattering, which are not well-defined because of a delta(z_\perp=0) singularity that is generated by QCD evolution. We study the single and double parton contributions to these processes, and show how to handle the singularity using factorization and operator renormalization. We compute the QCD evolution of double parton distribution functions (PDFs) due to mixing with single PDFs. The modified evolution of dPDFs at z_\perp=0, including generalized dPDFs for the non-forward case, is given in the appendix. We include a brief discussion of the experimental interpretation of dPDFs and how they can probe flavor, spin and color correlations of partons in hadrons.

hep-ph↗

arXiv2012

Measuring gravitational lensing of the cosmic microwave background using cross correlation with large scale structure

We cross correlate the gravitational lensing map extracted from cosmic microwave background measurements by the Wilkinson Microwave Anisotropy Probe (WMAP) with the radio galaxy distribution from the NRAO VLA Sky Survey (NVSS) by using a quadratic estimator technique. We use the full covariance matrix to filter the data, and calculate the cross-power spectra for the lensing-galaxy correlation. We explore the impact of changing the values of cosmological parameters on the lensing reconstruction, and obtain statistical detection significances at $>3σ$. The results of all cross correlations pass the curl null test as well as a complementary diagnostic test using the NVSS data in equatorial coordinates. We forecast the potential for Planck and NVSS to constrain the lensing-galaxy cross correlation as well as the galaxy bias. The lensing-galaxy cross-power spectra are found to be Gaussian distributed.

astro-ph.CO↗

arXiv2012

Electroweak Radiative Corrections to Higgs Production via Vector Boson Fusion using Soft-Collinear Effective Theory

Soft-collinear effective theory (SCET) is applied to compute electroweak radiative corrections to Higgs production via gauge boson fusion, q q -> q q H. There are several novel features which make this process an interesting application of SCET. The amplitude is proportional to the Higgs vacuum expectation value (VEV), and so is not a gauge singlet amplitude. Standard resummation methods require a gauge singlet operator and do not apply here. The SCET analysis requires operators with both collinear and soft external fields, with the Higgs VEV being described by an external soft ϕ field. There is a scalar soft-collinear transition operator in the SCET Lagrangian which contributes to the scattering amplitude, and is derived here.

hep-ph↗

arXiv2012

A QCD Analysis of Double Parton Scattering: Color Correlations, Interference Effects and Evolution

We derive a factorization formula for the double Drell-Yan cross section in terms of double parton distribution functions (dPDFs). Diparton flavor, spin and color correlations and parton-exchange interference terms contribute, even for unpolarized beams. Soft radiation effects are nontrivial for the color correlation and interference contributions, and are described by non-perturbative soft functions. We provide a field-theoretic definition of the quark dPDFs and study some of their basic properties, including discrete symmetries and their interpretation in a non-relativistic quark model. We calculate the renormalization group evolution of the quark dPDFs and of the soft functions. The evolution receives contributions from both ultraviolet and rapidity divergences. We find that color correlation and interference effects are Sudakov suppressed, greatly reducing the number of dPDFs needed to describe double parton scattering at high energy experiments.

hep-ph↗

arXiv2012

Electroweak Sudakov Corrections and the Top Quark Forward-Backward Asymmetry

The Standard Model (SM) prediction of the top quark forward backward asymmetry is shown to be slightly enhanced by a correction factor of 1.05 due to electroweak Sudakov (EWS) logarithms of the form (α/sin^2 θ_W)^n log^{m< 2n} (s/M_{W,Z}^2). The EWS effect on the dijet and t \bar{t} invariant mass spectra is significant, reducing the SM prediction by ~20, 10 % respectively for the highest invariant masses measured at the LHC, and changing the shape of the high-mass tail of the spectrum. These corrections significantly affect measurements of the top quark invariant mass spectrum and the search for an excess of events related to the top quark forward-backward asymmetry.

hep-ph↗

arXiv2011

The Topology and Size of the Universe from the Cosmic Microwave Background

We study the possibility that the universe has compact topologies T^3, T^2 x R^1, or S^1 x R^2 using the seven-year WMAP data. The maximum likelihood 95% confidence intervals for the size L of the compact direction are 1.7 < L/L_0 < 2.1, 1.8 < L/L_0 < 2.0, 1.2 < L/L_0 < 2.1 for the three cases, respectively, where L_0=14.4 Gpc is the distance to the last scattering surface. An infinite universe is compatible with the data at 4.3 sigma. We find using a Bayesian analysis that the most probable universe has topology T^2 x R^1, with L/L_0=1.9.

astro-ph.CO↗

arXiv2010

Hilbert Series for Flavor Invariants of the Standard Model

The Hilbert series is computed for the lepton flavor invariants of the Standard Model with three generations including the right-handed neutrino sector needed to generate light neutrino masses via the see-saw mechanism. We also compute the Hilbert series of the quark flavor invariants for the case of four generations.

hep-ph↗

arXiv2010

Constraining weak annihilation using semileptonic D decays

The recently measured semileptonic D_s decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D_{(s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |Vub| from inclusive semileptonic B decays.

hep-ph↗

arXiv2010

Reparametrization Invariance Constraints on Inclusive Decay Spectra and Masses

Reparametrization invariance relations are determined for the inclusive decay spectra of heavy hadrons. They connect the leading order result to the lambda_1 term, and the lambda_2 and rho_2 terms, and imply that the lambda_1 and rho_2 terms in the total rate occur in the combinations 1+lambda_1/(2m_Q^2) and lambda_2-rho_2/m_Q. The relations are satisfied by the known results for the hadronic decay tensors for B -> X e nu, B -> X gamma and B -> X e+ e- decays. An interesting field-theory result, the connection between currents in full and effective theories and the change in currents under field redefinitions, is discussed. The hadron masses are given to order (Lambda_QCD)^3/m_Q^2 including radiative corrections, and provide an example illustrating the relation between renormalization and reparametrization invariance and mu-independence of 1/m_Q^3 corrections to physical quantities.

hep-ph↗

arXiv2010

Radiative Corrections to Longitudinal and Transverse Gauge Boson and Higgs Production

Radiative corrections to gauge boson and Higgs production computed recently using soft-collinear effective theory (SCET) require the one-loop high-scale matching coefficients in the standard model. We give explicit expressions for the matching coefficients for the effective field theory (EFT) operators for q qbar -> VV and q qbar -> phi^+ phi for a general gauge theory with an arbitrary number of gauge groups. The group theory factors are given explicitly for the standard model, including both QCD and electroweak corrections.

hep-ph↗

arXiv2009

A Lattice Test of 1/N_c Baryon Mass Relations

1/N_c baryon mass relations are compared with lattice simulations of baryon masses using different values of the light-quark masses, and hence different values of SU(3) flavor-symmetry breaking. The lattice data clearly display both the 1/N_c and SU(3) flavor-symmetry breaking hierarchies. The validity of 1/N_c baryon mass relations derived without assuming approximate SU(3) flavor-symmetry also can be tested by lattice data at very large values of the strange quark mass. The 1/N_c expansion constrains the form of discretization effects; these are suppressed by powers of 1/N_c by taking suitable combinations of masses. This 1/N_c scaling is explicitly demonstrated in the present work.

hep-lat↗

arXiv2009

Soft and Collinear Functions for the Standard Model

Radiative corrections to high energy scattering processes were given previously in terms of universal soft and collinear functions. This paper gives the collinear functions for all standard model particles, the general form of the soft function, and explicit expressions for the soft functions for fermion-fermion scattering, longitudinal and transverse gauge boson production, single W/Z production, and associated Higgs production. An interesting subtlety in the use of the Goldstone boson equivalence theorem for longitudinal W+ production is discussed.

hep-ph↗