arXiv subjects

Alexey A. Petrov

Publications and source records attributed to Alexey A. Petrov.

At least 37 records · Page 2Linked to original sources

arXiv2020

Shining dark matter in Xenon1T

We point out that a non-relativistic $\sim 2 $ GeV dark matter (DM) which interacts with visible matter through higher dimensional Rayleigh operators could explain the excess of "electron recoil" events recently observed by the Xenon1T collaboration. A DM scattering event results in a few keV photon that on average carries most of the deposited energy, while the nuclear recoil energy is only a subleading correction. Since the Xenon1T detector does not discriminate between electrons and photons, such events would be interpreted as excess of the keV electrons. Indirect constraints from dark matter annihilation are avoided for light mediators of ${\mathcal O}(10~{\rm MeV})$ that have sizable couplings to neutrinos. One loop induced spin-independent scattering in dark matter may soon lead to a confirmation signal or already excludes regions of viable parameter space for the Rayleigh DM model, depending on what the exact values of the unknown nonperturbative nuclear matrix elements are.

hep-ph↗

arXiv2020

Semileptonic decays of heavy mesons with artificial neural networks

Experimental checks of the second row unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix involve extractions of the matrix element $V_{cd}$, which may be obtained from semileptonic decay rates of $D$ to $π$. These decay rates are proportional to hadronic form factors which parameterize how the quark $c \to d$ transition is realized in $D \to π$ meson decays. The form factors can not yet be analytically computed over the whole range of available momentum transfer $q^2$, but can be parameterized with a varying degree of model dependency. We propose using artificial neural networks trained from experimental pseudo-data to predict the shape of these form factors with a prescribed uncertainty. We comment on the parameters of several commonly-used model parameterizations of semileptonic form factors. We extract shape parameters and use unitarity to bound the form factor at a given $q^2$, which then allows us to bound the CKM matrix element $|V_{cd}|$.

hep-ph↗

arXiv2018

Studies of Lepton Flavor Violation at the LHC

We examine the charged lepton flavor violating process $gg \rightarrow μ^\pm τ^\mp$ at the $\sqrt{s} = 13$ TeV LHC. Operators generating this process can be induced by new physics (NP) at dimension 8. Despite the power suppression associated with dimension 8 operators, we show that the LHC's large gluon luminosity makes it possible to probe this channel. For an integrated luminosity of 100 fb$^{-1}$ at the LHC, we predict a constraint on the NP scale $Λ\gtrsim 3$ TeV. In addition, we point out that such operators can be induced through top quark loops in models that generate dimension 6 operators of the form $\overline{t} t \, μτ$. We find that the NP scale of these dimension 6 operators can be constrained to be $Λ\gtrsim 3.4-4.1$ TeV with 100 fb$^{-1}$ of data.

hep-ph↗

arXiv2017

Radiative lepton flavor violating B, D, and K decays

We argue that radiative lepton flavor violating (RLFV) decays $P \to γ\ell_1 \overline{\ell}_2$ of $P =B^0_q$, $\bar{D}^0$, and $K^0$ meson states are robust probes of new physics models. In particular, they could be used to put constraints on the Wilson coefficients of effective operators describing lepton flavor-changing neutral current interactions at low energy scales. We set up a generic framework for describing these transitions and review new physics constraints from $P \to \ell_1 \bar \ell_2$ decays. There is discussion of how RLFV transitions provide access to the operators that cannot be constrained in two-body decays and we in turn motivate further experimental searches via these channels.

hep-ph↗

arXiv2017

Direct CP asymmetry in $D\to π^-π^+$ and $D\to K^-K^+$ in QCD-based approach

We present the first QCD-based calculation of hadronic matrix elements with penguin topology determining direct CP-violating asymmetries in $D^0\to π^-π^+$ and $D^0\to K^- K^+$ nonleptonic decays. The method is based on the QCD light-cone sum rules and does not rely on any model-inspired amplitude decomposition, instead leaning heavily on quark-hadron duality. We provide a Standard Model estimate of the direct CP-violating asymmetries in both pion and kaon modes and their difference and comment on further improvements of the presented computation.

hep-ph↗

arXiv2017

Lepton flavor-violating transitions in effective field theory and gluonic operators

Lepton flavor-violating processes offer interesting possibilities to probe new physics at multi-TeV scale. We discuss those in the framework of effective field theory, emphasizing the role of gluonic operators. Those operators are obtained by integrating out heavy quarks that are kinematically inaccessible at the scale where low-energy experiments take place and make those experiments sensitive to the couplings of lepton flavor changing neutral currents to heavy quarks. We discuss constraints on the Wilson coefficients of those operators from the muon conversion $μ^- + (A,Z) \to e^- + (A,Z)$ and from lepton flavor-violating tau decays with one or two hadrons in the final state, e.g. $τ\to \ell \ η^{(\prime)}$ and $τ\to \ell \ π^+π^-$ with $\ell = μ, e$. To illustrate the results we discuss explicit examples of constraining parameters of leptoquark models.

hep-ph↗

arXiv2016

Lepton flavor violating quarkonium decays

We argue that lepton flavor violating (LFV) decays $M \to \ell_1 \overline \ell_2$ of quarkonium states $M$ with different quantum numbers could be used to put constraints on the Wilson coefficients of effective operators describing LFV interactions at low energy scales. We note that restricted kinematics of the two-body quarkonium decays allows us to select operators with particular quantum numbers, significantly reducing the reliance on the single operator dominance assumption that is prevalent in constraining parameters of the effective LFV Lagrangian. We shall also argue that studies of radiative lepton flavor violating $M \to γ\ell_1 \overline \ell_2$ decays could provide important complementary access to those effective operators.

hep-ph↗

arXiv2015

Resolving charm and bottom quark masses in precision Higgs boson analyses

Masses of the charm and bottom quarks are important inputs to precision calculations of Higgs boson observables, such as its partial widths and branching fractions. They constitute a major source of theory uncertainties that needs to be better understood and reduced in light of future high-precision measurements. Conventionally, Higgs boson observables are calculated in terms of $m_c$ and $m_b$, whose values are obtained by averaging over many extractions from low-energy data. This approach may ultimately be unsatisfactory, since $m_c$ and $m_b$ as single numbers hide various sources of uncertainties involved in their extractions some of which call for more careful estimations, and also hide correlations with additional inputs such as $α_s$. Aiming at a more detailed understanding of the uncertainties from $m_c$ and $m_b$ in precision Higgs boson analyses, we present a calculation of Higgs boson observables in terms of low-energy observables, which reveals concrete sources of uncertainties that challenge sub-percent-level calculations of Higgs boson partial widths.

hep-ph↗

arXiv2015

The role of low-energy observables in precision Higgs analysis

A conventional approach to precision calculations of Higgs boson observables uses quark masses $m_c$ and $m_b$ as inputs. However, quark masses are single numbers that hide a variety of low-energy data from which they are extracted, and also hide the various sources of theoretical uncertainties and correlations with additional input parameters such as $α_s$. Higher-precision calculations, which are needed to give meaning to future measurements, require more direct engagement with the low-energy data in a global analysis. We present an initial calculation in this direction, which illustrates the procedure and reveals some of the theory uncertainties that challenge subpercent determinations of Higgs boson partial widths.

hep-ph↗

arXiv2014

D^\pm Production Asymmetry at the LHC from Heavy-Quark Recombination

The asymmetry in the forward region production cross section of D^\pm is calculated using the heavy-quark recombination mechanism for pp collisions at 7 TeV. By suitable choices of four non-perturbative parameters, our calculated results can reproduce those obtained at LHCb. We find A_p ~ -1% when integrated over 2.0 GeV < p_T < 18 GeV and 2.2< eta <4.75, which agrees with A_p=-0.96\pm0.26\pm0.18% as measured by LHCb. Furthermore, the calculated distributions in eta and p_T agree reasonably well with those obtained at LHCb.

hep-ph↗

arXiv2014

Nonstandard neutrino interactions and transition magnetic moments

We constrain generic nonstandard neutrino interactions with existing experimental data on neutrino transition magnetic moments and derive strong bounds on tensorial couplings of neutrinos to charged fermions. We also discuss how some of these tensorial couplings can be constrained by other experiments, e.g., on neutrino-electron and neutrino-nucleus scattering.

hep-ph↗

arXiv2013

Shadowing near nonhyperbolic fixed points

We use Lyapunov type functions to find conditions of finite shadowing in a neighborhood of a nonhyperbolic fixed point of a one-dimensional or two-dimensional homeomorphism or diffeomorphism. A new concept of shadowing in which we control the size of one-step errors is introduced in the case of a nonisolated fixed point.

math.DS↗

arXiv2013

Lyapunov functions, shadowing, and topological stability

We use Lyapunov type functions to give new conditions under which a homeomorphism of a compact metric space has the shadowing property. These conditions are applied to establish the topological stability of some homeomorphisms with nonhyperbolic behavior.

math.DS↗

arXiv2013

Searching for dark matter at LHC with Mono-Higgs production

We consider LHC searches for dark matter in the mono-Higgs channel using the tools of effective field theory. This channel takes unique advantage of the presence of $SU(2)_L$ breaking in those operators to avoid the need for any initial-state radiation, usually necessary to tag the production of invisible particles. We find that sensitivities to parameters describing dark matter interactions with standard model particles are comparable to those from monojet searches for a subset of the usually-considered operators, and we present for the first time bounds from collider searches on operators which couple DM to only the Higgs field or its covariant derivatives.

hep-ph↗

arXiv2013

Faking $B_s \to μ^+μ^-$

Recent evidence from observation of the flavor-changing neutral current decay B_s to mu+ mu- by the LHCb collaboration B(B_s to mu^+ mu^-) = (3.2 * 10^{-9}), is consistent with the latest standard model prediction B(B_s to mu^+ mu^-) = (3.23 +- 0.27) * 10^{-9}. While New Physics can still affect this decay amplitude, its contribution is certainly not the dominant one. We analyze branching ratios of the decays B_s to mu+ mu- X, with X = a photon or neutrino anti-neutrino pair, which can mimic B_s to mu+ mu- on portions of the parameter space where X is soft. We perform a model-independent standard model calculation of those processes incorporating heavy quark and chiral symmetries of QCD. We show that the considered contributions contribute to B_s to mu+ mu- at a sub-percent level.

hep-ph↗

arXiv2012

Searching for super-WIMPs in leptonic heavy meson decays

We study constraints on the models of bosonic super-weakly interacting particle (super-WIMP) dark matter (DM) with DM masses $m_X \sim \mathcal{O}(1 - 100)$ keV from leptonic decays $M\rightarrow \ell \barν_\ell + X$, where $M=B^\pm, D^\pm, D_s^\pm$ is a heavy meson state. We focus on two cases where $X$ denotes either a light pseudoscalar (axion-like), or a light vector state that couples to the standard model (SM) through kinetic mixing. We note that for a small DM mass these decays are separately sensitive to DM couplings to quarks, but not its mass.

hep-ph↗

arXiv2010

The flavor puzzle in multi-Higgs models

We reconsider the flavor problem in the models with two Higgs doublets. By studying two generation toy models, we look for flavor basis independent constraints on Yukawa couplings that will give us the mass hierarchy while keeping all Yukawa couplings of the same order. We then generalize our findings to the full three generation Standard Model. We find that we need two constraints on the Yukawa couplings to generate the observed mass hierarchy, and a slight tuning of Yukawa couplings of order 10%, much less than the Standard Model. We briefly study how these constraints can be realized, and show how flavor changing currents are under control for $K-\bar{K}$ mixing in the near-decoupling limit.

hep-ph↗

arXiv2009

Primordial black holes and the observed Galactic 511 keV line

The observed 511 keV line from the Galactic Bulge is a real challenge for theoretical astrophysics: despite a lot of suggested mechanisms, there is still no convincing explanation and the origin of the annihilated positrons remains unknown. Here we discuss the possibility that a population of slowly evaporating primordial black holes with the mass around $10^{16}-10^{17}$ g ejects (among other particles) low--energy positrons into the Galaxy. In addition to positrons, we have also calculated the spectrum and number density of photons and neutrinos produced by such black holes and found that the photons are potentially observable in the near future, while the neutrino flux is too weak and below the terrestrial and extra--terrestrial backgrounds. Depending on their mass distribution, such black holes could make a small fraction or the whole cosmological dark matter.

astro-ph↗