arXiv subjects

Subhendra Mohanty

Publications and source records attributed to Subhendra Mohanty.

At least 37 records · Page 2Linked to original sources

arXiv2021

Evidence of dark energy in different cosmological observations

The idea of a negative-pressure dark energy component in the Universe which causes an accelerated expansion in the late Universe has deep implications in models of field theory and general relativity. In this article, we survey the evidence for dark energy from cosmological observations which started from the compilation of distance-luminosity plots of Type Ia supernovae. This turned out to be consistent with the dark energy inferred from the CMB observations and large scale surveys and gave rise to the concordance $Λ$CDM model of cosmology. In this article, we discuss the observational evidence for dark energy from Type Ia supernovae, CMB, galaxy surveys, observations of the Sunyaev-Zeldovich effect from clusters, and lensing by clusters. We also discuss the observational discrepancy in the values of $H_0$ and $σ_8$ between CMB and large scale structures and discuss if varying dark energy models are able to resolve these tensions between different observations.

astro-ph.CO↗

arXiv2021

Constraints on electromagnetic form factors of sub-GeV dark matter from the Cosmic Microwave Background anisotropy

We consider dark matter which have non-zero electromagnetic form factors like electric/magnetic dipole moments and anapole moment for fermionic dark matter and Rayleigh form factor for scalar dark matter. We consider dark matter mass $m_χ> \cal{ O}({\rm MeV})$ and put constraints on their mass and electromagnetic couplings from CMB and LSS observations. Fermionic dark matter with non-zero electromagnetic form factors can annihilate to $e^+ e^-$ and scalar dark matter can annihilate to $2γ$ at the time of recombination and distort the CMB. We analyze dark matter with multipole moments with Planck and BAO observations. We find upper bounds on anapole moment $g_{A}<7.163\times 10^{3} \text{GeV}^{-2}$, electric dipole moment ${\cal D}<7.978\times 10^{-9} \text{e-cm}$, magnetic dipole moment $μ<2.959\times 10^{-7} μ_B$, and the bound on Rayleigh form factor of dark matter is $g_4/Λ_4^2<1.085\times 10^{-2}\text{GeV}^{-2}$ with $95\%$C.L.

hep-ph↗

arXiv2021

Implications of the NANOGrav result on primordial gravitational waves in nonstandard cosmologies

Recently, the NANOGrav collaboration has reported evidence for a common-spectrum stochastic process, which might be interpreted as the first ever detection of stochastic gravitational wave (GW) background. We discuss the possibility of the signal arising from the first and second-order GWs in nonstandard cosmological history. We show that the NANOGrav observation can be explained by the first order GWs in the nonstandard thermal history with an early matter-dominated era, whereas the parameter space required to explain the NANOGrav observation in the standard cosmology or in the nonstandard epoch of kination domination is ruled out by the BBN and CMB observations. For the second-order GWs arising from the large primordial scalar fluctuations, we study the standard radiation domination and two specific nonstandard cases with a few forms of the primordial power spectrum $P_ζ(k)$ to achieve abundant primordial black hole (PBH) production. We find that the NANOGrav observation can be explained with standard radiation domination for all of these $P_ζ(k)$. Furthermore, a dustlike epoch leads to abundant PBH formation for a lower amplitude of $P_ζ(k)$ than the radiation dominated case and complies with the NANOGrav observation only for a few of the all $P_ζ(k)$ forms considered here, where the peak wavenumber is larger than the wavenumber range probed by the NANOGrav. In this nonstandard epoch, for a broad power spectrum, PBHs are produced in a wide mass range in the planetary mass regime. A nonstandard epoch of kination domination cannot produce enough PBH for any of the $P_ζ(k)$ if the NANOGrav result is to be satisfied.

astro-ph.CO↗

arXiv2021

Inflation and long-range force from clockwork $D$-term

Cosmic inflation driven by the vacuum energy associated with the $D$-term of a supersymmetric abelian gauge group and a possible existence of long-range force mediated by an ultra-light gauge boson $Z^\prime$ are two extreme examples of models based on extra $U(1)$ symmetries. Large vacuum energy sets the scale of inflation while the scales of long-range forces induced by anomaly free extra gauged $U(1)$ symmetries are constrained by neutrino oscillations, binary pulsar timings and invisible neutrino decay. There exists a difference of about 40 orders of magnitude between the scales of these two. Also, gauge couplings associated with the long-range forces are very small compared to the standard model couplings and the one required for inflation. We propose a framework based on clockwork mechanism in which these vastly different scales and associated new physics can coexist without invoking any arbitrarily small or large parameter in the fundamental theory. A chain of $U(1)$ is introduced with characteristic nearest-neighbour interactions. A large $D$-term introduced at one end governs the dynamics of inflation. $Z^\prime$ is localized on the other end of the chain, and it can be massless or can get naturally suppressed mass. The standard model fields can be charged under one of the intermediate $U(1)$ in the chain to give rise to their small effective coupling $g^\prime$ with $Z^\prime$. Constraints on $g^\prime$ and $M_{Z^\prime}$ are discussed in the context of the long-range forces of type $L_μ- L_τ$, $L_e - L_μ$ and $B-L$. These, along with the inflation observables, are used to constraint the parameters of the underlying clockwork model.

hep-ph↗

arXiv2020

Primordial black holes and gravitational waves in nonstandard cosmologies

For primordial black holes (PBHs) to form a considerable fraction of cold dark matter, the required amplitude of primordial scalar perturbations is quite large ($P_ζ(k) \sim 10^{-2}$) if PBH is formed in radiation epoch. In alternate cosmological histories, where additional epoch of arbitrary equation of state precede radiation epoch, the dynamics of PBH formation and relevant mass ranges can be different leading to lower requirement of primordial power at smaller scales of inflation. Moreover, this alternate history can modify the predictions for the gravitational wave (GW) spectrum, which can be probed by upcoming GW observations. In this paper, we show that an early kination epoch can lead to per cent level abundance ofPBH for a lower amplitude of $P_ζ(k)$ compared to PBH formation in a standard radiation epoch. Moreover, we calculate the effect of early kination epoch on the GW spectrum for first and second orders in perturbation theory which show enhancement in the amplitude of the GW spectrum in a kination epoch with respect to that in a standard radiation epoch.

astro-ph.CO↗

arXiv2020

Constraints on long range force from perihelion precession of planets in a gauged $L_e-L_{μ,τ}$ scenario

The standard model particles can be gauged in an anomaly free way by three possible gauge symmetries namely ${L_e-L_μ}$, ${L_e-L_τ}$, and ${L_μ-L_τ}$. Of these, ${L_e-L_μ}$ and ${L_e-L_τ}$ forces can mediate between the Sun and the planets and change the perihelion precession of planetary orbits. It is well known that a deviation from the $1/r^2$ Newtonian force can give rise to a perihelion advancement in the planetary orbit, for instance, as in the well known case of Einstein's gravity which was tested from the observation of the perihelion advancement of the Mercury. We consider the long range Yukawa potential which arises between the Sun and the planets if the mass of the gauge boson is $M_{Z^{\prime}}\leq \mathcal{O}(10^{-19})\rm {eV}$. We derive the formula of perihelion advancement for Yukawa type fifth force due to the mediation of such $U(1)_{L_e-L_{μ,τ}}$ gauge bosons. The perihelion advancement for Yukawa potential is proportional to the square of the semi major axis of the orbit for small $M_{Z^{\prime}}$, unlike GR, where it is largest for the nearest planet. However for higher values of $M_{Z^{\prime}}$, an exponential suppression of the perihelion advancement occurs. We take the observational limits for all planets for which the perihelion advancement is measured and we obtain the upper bound on the gauge boson coupling $g$ for all the planets. The Mars gives the stronger bound on $g$ for the mass range $\leq 10^{-19}\rm{eV}$ and we obtain the exclusion plot. This mass range of gauge boson can be a possible candidate of fuzzy dark matter whose effect can therefore be observed in the precession measurement of the planetary orbits.

hep-ph↗

arXiv2020

Supergravity Model of Inflation and Explaining IceCube HESE Data via PeV Dark Matter Decay

We construct an unified model of inflation and PeV dark matter with an appropriate choice of no-scale Kähler potential, superpotential and gauge kinetic function in terms of MSSM fields and hidden sector Polonyi field. The model is consistent with the CMB observations and can explain the PeV neutrino flux observed at IceCube HESE. A Starobinsky like Higgs-sneutrino plateau inflation is obtained from the $D$-term SUGRA potential while $F$-term being subdominant during inflation. To get PeV dark matter, SUSY breaking at PeV scale is achieved through Polonyi field. This sets the scale for soft SUSY breaking parameters $m_0, m_{1/2}, A_0 $ at the GUT scale in terms of the parameters of the model. The low energy particles spectrum is obtained by running the RGEs. We show that the $\sim$125 GeV higgs and the gauge coupling unification can be obtained in this model. The $6$ PeV bino-type dark matter is a subdominant fraction ($\sim 11\%$) of the relic density and its decay gives the PeV scale neutrino flux observed at IceCube by appropriately choosing the couplings of the $R$-parity violating operators. Also we find that there is a degeneracy in scalar field parameters $(γ, β)$ and coupling $ζ$ value in producing the correct amplitude of CMB power spectrum. However the value of parameter $\tan(β)=1.8$, which is tightly fixed from the requirement of PeV scale SUSY breaking, removes the degeneracy in the values of the scalar field parameters to provide a unique solution for inflation. In this way it brings the explanation for dark matter, PeV neutrinos and inflation within the same framework.

hep-ph↗

arXiv2020

Probing angle of birefringence due to long range axion hair from pulsars

Rotating neutron star or pulsar can be a possible source of pseudo Nambu Goldstone bosons or axions which can mediate long range axionic hair outside of the pulsar. When the electromagnetic radiation is emitted from pulsar and passes through the long range axion hair, the axion rotates the polarization of the electromagnetic radiation and produces birefringence. We obtain the angle of birefringence due to this long range axionic hair as $0.42^\circ$. This result is independent of the rotational frequency, radius of the pulsar, mass of the axion, and axion photon coupling constant. This value is within the accuracy of measuring the linear polarization angle of pulsar light which is $\leq 1.0^\circ$. Our result continues to hold as long as the range of the axion hair (inverse of axion mass) is greater than the radius of the pulsar, i.e; $m_a<10^{-11}$eV and the axion decay constant $f_a\lesssim \mathcal{O}(10^{17}\rm{GeV})$.

hep-ph↗

arXiv2020

Inflation models in the light of self-interacting sterile neutrinos

Short baseline neutrino experiments, like LSND and MiniBooNE experiments, pointed towards the existence of eV mass scale sterile neutrinos. To reconcile sterile neutrinos with cosmology self interaction between sterile neutrinos has been studied. We analysed Planck cosmic microwave background (CMB) data with self-interacting sterile neutrino (SI$ν$) and study their impact on inflation models. The fit to the CMB data in SI$ν$ model is as good as the fit to $Λ$CDM model. We find that the spectral index ($n_s$) values shift to $0.9361\pm 0.0055$ in SI$ν$ model. This has significant impact on the validity of different inflation models. For example the Starobinsky and quartic hilltop model, which were allowed within $Λ$CDM cosmology, are ruled out. On the other hand some models like natural and Coleman-Weinberg inflation are now favoured. Therefore, the existence of self interacting sterile neutrinos with eV order of mass will play an important role in the selection of correct inflation model.

astro-ph.CO↗

arXiv2020

Constraints on ultra-light axions from compact binary systems

Ultra light particles $(m_a \sim 10^{-21}eV-10^{-22}eV)$ with axion-like couplings to other particles can be candidates for fuzzy dark matter (FDM) if the axion decay constant $f_a\sim 10^{17}GeV$. If a compact star is immersed in such a low mass axionic potential it develops a long range field outside the star. This axionic field is radiated away when the star is in a binary orbit. The orbital period of a compact binary decays mainly due to the gravitational wave radiation, which was confirmed first in the Hulse-Taylor binary pulsar. The orbital period can also decay by radiation of other light particles like axions and axion like particles(ALPs). For axionic radiation to take place, the orbital frequency of the periodic motion of the binary system should be greater than the mass of the scalar particle which can be radiated. This implies that, for most of the observed binaries, particles with mass $m_a< 10^{-19}eV$ can be radiated, which includes FDM particles. In this paper, we consider four compact binary systems: PSR J0348+0432, PSR J0737-3039, PSR J1738+0333, and PSR B1913+16 (Hulse Taylor Binary) and show that the observations of the decay in orbital period put the bound on axion decay constant, $f_a\lesssim \mathcal{O}(10^{11}GeV)$. This implies that Fuzzy Dark Matter cannot couple to gluons.

hep-ph↗

arXiv2020

Test of Kerr-Sen metric with black hole observations

The Kerr-Sen black hole is a rotating charged black hole solution arising from heterotic string theory. In 4-dimensions effective theory the bosonic fields are: a $U(1)$ gauge boson, a Kalb-Ramond 3-form which is equivalent to a pseudoscalar axion in 4-dimensions, the dilaton and the graviton. The coupling constants in the theory are $α^{\prime}$ (inverse string tension) and $κ$ (inverse reduced Planck mass in 4-dimensions) and the charge of the $U(1)$ field and the axion-photon coupling are related to these two. Sen found a black hole solution (the Kerr-Sen black hole) with these fields as the external hair of the black hole. In this paper we investigate the possibility of determining the Sen solution from observations. The observations which can test the Kerr-Sen black hole are: (a) determination of the shape of the photon shadow, and (b) the rotation of polarization of photon due to axion hair. The deviation from circularity gives the $U(1)$ charge of the black hole and identification of this charge in terms of the photon coupling leads to a prediction of frequency independent "Faraday rotation" in terms of black hole parameters already determined from the shadow. Similar measurements of Kerr-Newman black hole with axion hair have no correlation between the shape of the image and the amount of "Faraday rotation". This correlation can be a distinctive test of the Sen metric. In the recent observation from EHT of M87* shadow, the deviation from circularity has an upper bound of 10%. If this observation is refined to 1% accuracy then a definitive prediction of the charge of the Kerr-Sen black hole and the "Faraday rotation" can be made. Interestingly observations of "Faraday rotation" have shown that the effect is independent of frequency pointing to an axionic hair interpretation for the effect.

gr-qc↗

arXiv2019

Vector gauge boson radiation from compact binary systems in a gauged $L_μ-L_τ$ scenario

The orbital period of a compact binary system decays mainly due to quadrupole gravitational radiation, which agrees with the observation to within one percent. Other types of radiation such as ultralight scalar or pseudoscalar radiation, massive vector boson radiation also contribute to the decay of orbital period as long as the mass of the emitted particle is less than the orbital frequency of the compact binary system. We obtain an expression of the energy loss due to the radiation of massive vector field from the neutron star-neutron star and neutron star-white dwarf binaries. Due to large chemical potential of the degenerate electrons, neutron stars have large muon charge. We derive the energy loss due to $U(1)_{L_μ-L_τ}$ gauge boson radiation from the binaries. For the radiation of vector boson, the mass is restricted by $M_{Z^\prime}<Ω\simeq10^{-19}eV$ are the orbital frequencies of the compact star binaries. Using the formula of orbital period decay, we obtain constraints on the coupling constant of the gauge boson in the gauged $L_μ-L_τ$ theory for the four compact binary systems. For vector gauge boson muon coupling we find that for $M_{Z^\prime}<10^{-19}eV$, constraints on the coupling constant is $g<\mathcal{O}(10^{-20})$. We also obtain the exclusion plots of the massive vector proca field and the gauge field which can couple to muons.

hep-ph↗

arXiv2019

MeV scale model of SIMP dark matter, neutrino mass and leptogenesis

We consider a simple extension of the Standard Model with two singlet scalar fields and three heavy right-handed neutrinos. One of the scalar fields serves as an MeV scale dark matter and its stability is ensured by the introduction of an extra $Z_2$ symmetry. The second scalar (which is even under the $Z_2$ symmetry) generates the mass term of the scalar, contributes to the $3 \rightarrow 2$ annihilation process required for the correct relic density of the dark matter and it also contributes to the leptogenesis. The right-handed neutrinos are responsible for the generation of light neutrino masses through Type-I seesaw mechanism. The decay of the heavy right-handed neutrino can generate the lepton asymmetry which can then be converted to baryon asymmetry through sphaleron transitions.

hep-ph↗

arXiv2019

Leptoquark solution for both the flavor and ANITA anomalies

The ANITA experiment has seen anomalous Earth emergent showers of EeV energies which cannot be explained with Standard Model interactions. In addition, tests of lepton flavor universality in $ R(D^{(\ast)})$ and $R(K^{(\ast)})$ have shown significant deviations from theoretical predictions. It is known that, among single leptoquark solutions, only the chiral vector leptoquark $U_1 \sim (\mathbf{3}, \mathbf{1} , 2/3)$ can simultaneously address the discrepancies. In this paper, we show that the leptoquark motivated by flavor anomalies coupled to a sterile neutrino can also explain the ANITA Anomalous Events. We consider two scenarios, (a) the sterile neutrino, produced via resonant leptoquark mediated neutrino-nucleon interactions, propagates through the Earth without significant attenuation and decays near the surface to a $τ$ lepton; and (b) a cosmogenic sterile neutrino interacts with the matter near the surface of Earth and generates a $τ$ lepton. These two scenarios give significantly large survival probabilities even when regeneration effects are not taken into account. In the second scenario, the distribution of emergent tau energy peaks in the same energy range as seen by ANITA.

hep-ph↗

arXiv2019

Cutoff of IceCube Neutrino Spectrum due to t-channel Resonant Absorption by C$ν$B

The non-observation of neutrinos by the IceCube at the Glashow resonance energy of 6.3 PeV has been a long standing unresolved issue. In this paper we propose a t-channel neutrino absorption by the C$ν$B, which causes a cutoff at 4.5 PeV neutrino energy, to explain the IceCube observations. We present a neutrinophilic 2HDM where the neutrino masses are generated by a low scale seesaw mechanism. A $\mathcal{O}$(10) MeV scalar mediates the interactions between left and right handed neutrinos and generates the t-channel diagram used for explaining the absence of Glashow resonance. The same scalar mediates the annihilation of the dark matter and generates the correct relic density.

hep-ph↗

arXiv2019

Constraints on $f(R)$ theories of gravity from GW170817

A novel constraint on $f(R)$ theories of gravity is obtained from the gravitational wave signal emitted from the binary neutron star merger event GW170817. The $f(R)$ theories possess an additional massive scalar degree of freedom apart from the massless spin-2 modes. The corresponding scalar field contributes an additional attractive, short-ranged "fifth" force affecting the gravitational wave radiation process. We realize that chameleon screening is necessary to conform with the observation. A model independent bound $\vert f'(R_0) -1\vert < 3\times 10^{-3}$ has been obtained, where the prime denotes the derivative with respect $R$ and $R_0$ is the curvature of our Universe at present. Though we use the nonrelativistic approximations and obtain an order of magnitude estimate of the bound, it comes from direct observations of gravitational waves and thus it is worth noting. This bound is stronger/equivalent compared to some earlier other bounds such as from the Cassini mission in the Solar-System, Supernova monopole radiation, the observed CMB spectrum, galaxy cluster density profile, etc., although it is weaker than best current constraints ($\vert f'(R_0) -1\vert \lesssim 10^{-6}$) from cosmology. Using the bound obtained, we also constrain the parameter space in the $f(R)$ theories of dark energy like Hu-Sawicki, Starobinsky, and Tsujikawa models.

gr-qc↗

arXiv2018

Signature of light sterile neutrinos at IceCube

The MiniBooNe collaboration has recently reported evidence for a light sterile neutrino with large mixing angles thus corroborating the measurement by LSND twenty years ago. Such a state would be directly in conflict with Planck measurement of BBN $N_{eff}$ unless there is self-interaction in the sterile sector. Our objective is to investigate if such interactions could result in resonant absorption in the cosmogenic neutrino spectrum and its consequences for the IceCube experiment. We show that it is possible to give independent bounds on sterile neutrino parameter space from IceCube observations with the dips in the spectrum corresponding to the neutrino masses.

hep-ph↗

arXiv2018

Explanation of IceCube spectrum with $ν\rightarrow 3 ν$ neutrino splitting in a $ν$2HDM model

A single power law flux spectrum of high energy neutrinos does not adequately explain the entire 60 TeV to 10 PeV event spectrum observed at IceCube, specially the excess of PeV events and the lack of Glashow resonance events expected at 6.3 PeV cannot be simultaneously explained by a single power law source neutrino flux. Here we consider a model of neutrino splitting $ν\rightarrow 3 ν$ over cosmological distances. Starting from a single power-law spectrum expected from the astrophysical sources, we show that by adjusting the decay length and spectral index one can give a better fit to the observed IceCube events over the entire 1 TeV -6 PeV, compared to that from a single power spectrum. For $ν\rightarrow 3ν$ neutrino splitting, the flavor ratios of the daughter neutrinos are different from the standard oscillation or invisible decay cases and can be used as a test of this scenario. We propose a $ν$2HDM where a light Higgs ($\sim 0.1$~eV) mediates neutrino splitting via a one-loop box diagram. The split in the masses of the scalars in the doublet gives a large contribution to the oblique T parameter which is severely constrained. This constraint from the S,T,U oblique parameters can be evaded by the introduction of an extra vector lepton doublet and with mass $\sim 200$ GeV.

hep-ph↗