arXiv subjects

Mohammadreza Zakeri

Publications and source records attributed to Mohammadreza Zakeri.

At least 19 recordsLinked to original sources

arXiv2025

Does the Sun have a Dark Disk?

The Sun is not quite a perfect sphere, and its oblateness, thought to be induced through its rotation, has been measured using optical observations of its radius. Its gravitational quadrupole moment can then be deduced using solar models, or through helioseismology, and it can also be determined from measurements of its gravitational effects on Mercury's orbit. The various assessments do not appear to agree, with the most complete and precise orbital assessments being in slight excess of other determinations. This may speak to the existence of a non-luminous disk or ring, where we also note evidence for a circumsolar dust ring within Mercury's orbit from the Solar TErrestrial RElations Observatory (STEREO) mission. Historically, too, a protoplanetary disk may have been key to reconciling the Sun's metallicity with its neutrino yield. The distribution of the non-luminous mass within Mercury's orbit can modify the relative size of the optical and orbital quadrupole moments in different ways. We develop how we can use these findings to limit the mass of a dark disk, ring, or halo in the immediate vicinity of the Sun, and we note how future observational studies of the inner solar system can not only refine these constraints but also help to identify and to assess the mass of its dark-matter component.

hep-ph↗

arXiv2024

Insights from Binary Pulsars and Laboratories into Baryon Number Violation: Implications for GeV Dark Matter

Rare processes in laboratory and within astrophysical environments can be highly sensitive probes of baryon-number violating interactions at the TeV scale. We demonstrate the power of neutron stars to constrain baryon number violation by considering a minimal extension of the standard model involving a TeV-mass scalar mediator and a GeV scale Majorana fermion $ψ$. We find that a $ΔB = 2$ mass-loss process in binary pulsar systems via $n \to γψ$ and the subsequent scattering $ψn \to π^- K^+$ places stringent constraints on the model parameter space. These limits will become much stronger, due to the possibility of $Λ\rightarrow γψ$ decays at the tree level, if the neutron star equation of state is hyperonic. We compare these constraints with ongoing and future collider experiments, $n-\bar{n}$ oscillations, and dinucleon decay searches at future large-scale neutrino experiments, finding that the binary pulsars bounds on couplings are significantly tighter for specific flavor combinations.

hep-ph↗

arXiv2024

Pulsar Timing Anomalies: A Window into Baryon Number Violation

We investigate the influence of a specific class of slow Baryon Number Violation (BNV) -- one that induces quasi-equilibrium evolution -- on pulsar spin characteristics. This work reveals how BNV can potentially alter observable parameters, including spin-down rates, the second derivative of spin frequency, and braking indices of pulsars. Moreover, we demonstrate that BNV could lead to anomalies in pulsar timing, along with a wide array of braking indices, both positive and negative. In addition, we examine the possibility of pulsar spin-up due to BNV, which may result in a novel mechanism for the revival of ``dead'' pulsars. We conclude by assessing the sensitivity required for future pulsar timing efforts to detect such BNV effects, thus highlighting the potential for pulsars to serve as laboratories for testing fundamental physics.

astro-ph.HE↗

arXiv2024

Probing Dark Sectors with Neutron Stars

Tensions in the measurements of neutron and kaon weak decays, such as of the neutron lifetime, may speak to the existence of new particles and dynamics not present in the Standard Model (SM). In scenarios with dark sectors, particles that couple feebly to those of the SM appear. We offer a focused overview of such possibilities and describe how the observations of neutron stars, which probe either their structure or dynamics, limit them. In realizing these constraints, we highlight how the assessment of particle processes within dense baryonic matter impacts the emerging picture -- and we emphasize both the flavor structure of the constraints and their broader connections to cogenesis models of dark matter and baryogenesis.

hep-ph↗

arXiv2024

How Macroscopic Limits on Neutron Star Baryon Loss Yield Microscopic Limits on Non-Standard-Model Baryon Decay

We investigate how our baryon-loss limits from anomalous binary-pulsar period lengthening can be interpreted microscopically to yield specific constraints on the particle physics of baryon number violation within a neutron star. We focus on the possibility of anomalous baryon disappearance via dark baryon processes and on scenarios in which the produced dark-sector particles do not survive to influence the response of the star to baryon-number-violating effects. We flesh out the conditions for which this may occur, as well as other key assumptions. We then turn to the analysis of particle processes in the dense nuclear medium found at the core of a neutron star, employing the techniques of relativistic mean-field theory. Using our study of in-medium effects and limits on macroscopic baryon number violation we extract limits on in-vacuum baryon-number-violating processes, and we determine them for various equations of state. We conclude by noting the implications of our results for models of dark-sector-enabled baryogenesis.

hep-ph↗

arXiv2022

Constraining Time Dependent Dark Matter Signals from the Sun

Dark matter (DM) particles captured by the Sun can produce high energy electrons outside the Sun through annihilating into meta-stable mediators. The corresponding cosmic-ray electron signals observed by the space-based experiments will be time dependent due to the orbital motion of the space-based detectors. The shape of this time dependence is predictable given the orbital information of the detectors. Since the high-energy CR electron (with energy E>100 GeV) fluxes are expected to be constant in time, non-observation of such time variation can be used to place upper limits on the DM annihilation cross section. We analyze the time dependence of dark matter cosmic-ray signals in three space-based experiments: AMS-02, DAMPE and CALET. Under the assumption that no time dependent signal is observed, we derive the 95% C.L. exclusion limits on the signal strength from the current data. We map our limits onto the parameter space of the dark photon model and find that the constraints are comparable with that derived from the supernova SN1987A.

hep-ph↗

arXiv2022

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we use it as motivation for a broader review of the ways that baryon number violation, be it real or apparent, and dark sectors can intertwine and how neutron star observables, both present and future, can constrain them.

hep-ph↗

arXiv2020

Non-Abelian Vector Boson as FIMP Dark Matter

In this analysis we demonstrate the freeze-in realization of a non-abelian vector boson dark matter (DM). We choose to elaborate an existing $SU(2)_N$ extension ($N$ stands for neutral) of the Standard Model (SM) with an additional $U(1)=S^{'}$ global symmetry, which stabilizes the vector boson ($X,\bar{X}$) as DM through unbroken $S=T_{3N}+S^{'}$ and as lightest odd $S$ particle. The analysis reveals that the contribution to the freeze-in production of DM from the decay of a heavier scalar bidoublet $ζ_1^{0,\pm} \to ζ_2^{0,\pm}X$ is important even after the freeze-out of $ζ_1^{0,\pm}$ in equilibrium with thermal bath. Moreover, the neutral component of $SU(2)_N$ scalar triplet ($Δ$), responsible for neutrino mass generation in this framework, turns out to serve as additional DMs in the model and offers a multipartite freeze-in DM set up to explore. The allowed parameter space is obtained after estimating constraints from CMB, BBN and AMS-02 bound. This exercise nicely complements the freeze-out realization of ($X,\bar{X}$) as weakly interacting massive particle (WIMP) and distinguishes it through stable charge track signature at collider compared to leptonic signal excess as found in WIMP scenario.

hep-ph↗

arXiv2019

Exotic Lepton-Flavor Violating Higgs Decays

Exotic Higgs decays are promising channels to discover new physics in the near future. We present a simple model with a new light scalar that couples to the Standard Model through a charged lepton-flavor violating interaction. This can yield exciting new signatures, such as $h \to e^+ e^+ μ^-μ^-$, that currently have no dedicated searches at the Large Hadron Collider. We discuss this model in detail, assess sensitivity from flavor constraints, explore current constraints from existing multi-lepton searches, and construct a new search strategy to optimally target these exotic, lepton-flavor violating Higgs decays.

hep-ph↗

arXiv2018

Multipartite Dark Matter in $SU(2)_N$ extension of Standard Model and signatures at the LHC

An $SU(2)_N$ extension ($N$ stands for neutral) of the Standard Model (SM) is proposed with an additional $U(1)=S^{'}$ global symmetry, which stabilizes the lightest of the vector boson ($X,\bar{X}$) as dark matter (DM) through unbroken $S=T_{3N}+S^{'}$. The field content of the model is motivated to address neutrino mass generation, a possible unification to $SU(7)$, along with spontaneous symmetry breaking of $SU(2)_N$ resulting in massive gauge bosons. None of the SM particles are charged under $SU(2)_N$ and therefore $X,\bar{X}$ do not have a direct coupling to the visible sector besides a Higgs portal, which is tiny to avoid any conflict with Higgs data. We show that, a large kinematic region of this model allows the neutral component of $SU(2)_N$ scalar triplet and heavy neutrinos introduced here to become additional DM components. In this paper we explore the viability of such multipartite DM parameter space, including non-zero DM-DM interactions, to comply with relic density and direct search constraints. We also demonstrate that the model may yield hadronically quiet single lepton and two lepton signatures with missing energy at the Large Hadron Collider (LHC) that can be accessed with high luminosity.

hep-ph↗

arXiv2018

A Minimal Model For Two-Component FIMP Dark Matter: A Basic Search

In the multi-component configurations of dark matter phenomenology, we propose a minimal two-component configuration which is an extension of the Standard Model with only three new fields; one scalar and one fermion interact with the thermal soup through Higgs portal, mediated by the other scalar in such a way that the stabilities of dark matter candidates are made simultaneously by an explicit $Z_2$ symmetry. Against the most common freeze-out framework, we look for dark matter particle signatures in the freeze-in scenario by evaluating the relic density and detection signals. A simple distinguishing feature of the model is the lack of dark matter conversion, so the dark matter components act individually and the model can be adapted entirely to both singlet scalar and singlet fermionic models, separately. We find dark matter self-interaction as the most promising approach to probe such feeble models. Although the scalar component satisfies this constraint, the fermionic one refuses it even in the resonant region.

hep-ph↗

arXiv2018

Alternative $[SU(3)]^4$ Model of Leptonic Color and Dark Matter

The alternative $[SU(3)]^4$ model of leptonic color and dark matter is discussed. It unifies at $M_U \sim 10^{14}$ GeV and has the low-energy subgroup $SU(3)_q \times SU(2)_l \times SU(2)_L \times SU(2)_R \times U(1)_X$ with $(u,h)_R$ instead of $(u,d)_R$ as doublets under $SU(2)_R$. It has the built-in global $U(1)$ dark symmetry which is generalized $B-L$. In analogy to $SU(3)_q$ quark triplets, it has $SU(2)_l$ hemion doublets which have half-integral charges and are confined by $SU(2)_l$ gauge bosons (stickons). In analogy to quarkonia, their vector bound states (hemionia) are uniquely suited for exploration at a future $e^-e^+$ collider.

hep-ph↗

arXiv2017

Dark Revelations of the $[SU(3)]^3$ and $[SU(3)]^4$ Gauge Extensions of the Standard Model

Two theoretically well-motivated gauge extensions of the standard model are $SU(3)_C \times SU(3)_L \times SU(3)_R$ and $SU(3)_q \times SU(3)_L \times SU(3)_l \times SU(3)_R$, where $SU(3)_q$ is the same as $SU(3)_C$ and $SU(3)_l$ is its color leptonic counterpart. Each as three variations, according to how $SU(3)_R$ is broken. It is shown here for the first time that a built-in dark $U(1)_D$ gauge symmetry exists in all six versions, and may be broken to discrete $Z_2$ dark parity. The available dark matter candidates in each case include fermions, scalars, as well as {\it vector gauge bosons}. This work points to the unity of matter with dark matter, the origin of which is not {\it ad hoc}.

hep-ph↗

arXiv2017

Dark Gauge U(1) Symmetry for an Alternative Left-Right Model

An alternative left-right model of quarks and leptons, where the $SU(2)_R$ lepton doublet $(ν,l)_R$ is replaced with $(n,l)_R$ so that $n_R$ is not the Dirac mass partner of $ν_L$, has been known since 1987. Previous versions assumed a global $U(1)_S$ symmetry to allow $n$ to be identified as a dark-matter fermion. We propose here a gauge extension by the addition of extra fermions to render the model free of gauge anomalies, and just one singlet scalar to break $U(1)_S$. This results in two layers of dark matter, one hidden behind the other.

hep-ph↗

arXiv2017

Quartified Leptonic Color, Bound States, and Future Electron-Positron Collider

The $[SU(3)]^4$ quartification model of Babu, Ma, and Willenbrock (BMW), proposed in 2003, predicts a confining leptonic color $SU(2)$ gauge symmetry, which becomes strong at the keV scale. It also predicts the existence of three families of half-charged leptons (hemions) below the TeV scale. These hemions are confined to form bound states which are not so easy to discover at the Large Hadron Collider (LHC). However, just as $J/ψ$ and $Υ$ appeared as sharp resonances in $e^-e^+$ colliders of the 20th century, the corresponding 'hemionium' states are expected at a future $e^-e^+$ collider of the 21st century.

hep-ph↗

arXiv2016

Generalized Gauge U(1) Family Symmetry for Quarks and Leptons

If the standard model of quarks and leptons is extended to include three singlet right-handed neutrinos, then the resulting fermion structure admits an infinite number of anomaly-free solutions with just one simple constraint. Well-known examples satisfying this constraint are $B-L$, $L_μ-L_τ$ , $B-3L_τ$ , etc. We derive this simple constraint, and discuss two new examples which offer some insights to the structure of mixing among quark and lepton families, together with their possible verification at the Large Hadron Collider.

hep-ph↗

arXiv2016

Verifiable Associated Processes from Radiative Lepton Masses with Dark Matter

If leptons do not couple directly to the one Higgs doublet of the standard model of particle interactions, they must still do so somehow indirectly to acquire mass, as proposed recently in several models where it happens in one loop through dark matter. We analyze the important consequences of this scenario in a specific model, including Higgs decay, muon anomalous magnetic moment, $μ\to e γ$, $μ\to eee$, and the proposed dark sector.

hep-ph↗

arXiv2016

Gauge $B-L$ Model of Radiative Neutrino Mass with Multipartite Dark Matter

We propose an extension of the standard model of quarks and leptons to include gauge $B-L$ symmetry with an exotic array of neutral fermion singlets for anomaly cancellation. With the addition of suitable scalars also transforming under $U(1)_{B-L}$, this becomes a model of radiative seesaw neutrino mass with possible multipartite dark matter. If leptoquark fermions are added, necessarily also transforming under $B-L$, the diphoton excess at 750 GeV, recently observed at the Large Hadron Collider, may also be explained.

hep-ph↗