Search

We present a cosmological model arising from a gravitational theory with an infinite tower of higher-order curvature invariants that can reproduce the entire evolution of the Universe: from inflation to late-time acceleration, without invoking an inflaton nor a cosmological constant. The theory is Einsteinian-like. The field equations for a Friedmann-Lema\^{i}tre-Robertson-Walker metric are of second-order and can reproduce a late-time evolution that is consistent with the acceleration provided by the cosmological constant at low redshift. Our results force us to reinterpret the nature of dark energy, becoming a mechanism that is inherited solely from the geometry of spacetime., Comment: Accepted in Physics Letters B. 13 pages, 4 figures

In the paradigm of effective field theory, one hierarchically obtains the effective action $\mathcal{A}_{\rm eff}[q, \cdots]$ for some low(er) energy degrees of freedom $q$, by integrating out the high(er) energy degrees of freedom $\xi$, in a path integral, based on an action $\mathcal{A}[q,\xi, \cdots]$. We show how one can integrate out a vector field $v^a$ in an action $\mathcal{A}[\Gamma,v,\cdots ]$ and obtain an effective action $\mathcal{A}_{\rm eff}[\Gamma, \cdots]$ which, on variation with respect to the connection $\Gamma$, leads to the Einstein's field equations and a metric compatible with the connection. The derivation \textit{predicts} a non-zero, positive, \cc, which arises as an integration constant. The Euclidean action $\mathcal{A}[\Gamma,v, \cdots]$, has an interpretation as the heat density of null surfaces, when translated into the Lorentzian spacetime. The vector field $v^a$ can be interpreted as the Euclidean analogue of the microscopic degrees of freedom hosted by any null surface. Several implications of this approach are discussed., Comment: Published Version; 12 pages; Prof. T. Padmanabhan has passed away on 17th September, 2021, while this paper was under review in a journal

Primordial black holes (PBHs) from the early Universe have been connected with the nature of dark matter and can significantly affect cosmological history. We show that coincidence dark radiation and density fluctuation gravitational wave signatures associated with evaporation of $\lesssim10^9$ g PBHs can be used to explore and obtain important hints about the formation mechanisms of spinning and non-spinning PBHs spanning orders of magnitude in mass-range, which is challenging to do otherwise., Comment: 7 pages, 1 figure; matches published version

Primordial black holes (PBHs) from the early Universe constitute a viable dark matter (DM) candidate and can span many orders of magnitude in mass. Light PBHs with masses around $10^{15}$ g contribute to DM and will efficiently evaporate through Hawking radiation at present time, leading to a slew of observable signatures. The emission will deposit energy and heat in the surrounding interstellar medium. We revisit the constraints from dwarf galaxy heating by evaporating non-spinning PBHs and find that conservative constraints from Leo T dwarf galaxy are significantly weaker than previously suggested. Furthermore, we analyse gas heating from spinning evaporating PBHs. The resulting limits on PBH DM abundance are found to be stronger for evaporating spinning PBHs than for non-spinning PBHs., Comment: 7 pages, 2 figures; published version

We study the structure of galactic halos within a scalar dark matter model, endowed with a repulsive quartic self-interaction, capable of undergoing the superfluid phase transition in high-density regions. We demonstrate that the thermalized cores are prone to fragmentation into superfluid droplets due to the Jeans instability. Furthermore, since cores of astrophysical size may be generated only when most of the particles comprising the halo reside in a highly degenerate phase-space, the well-known bound on the dark matter self-interaction cross section inferred from the collision of clusters needs to be revised, accounting for the enhancement of the interaction rate due to degeneracy. As a result, generation of kpc-size superfluid solitons, within the parameter subspace consistent with the Bullet Cluster bound, requires dark matter particles to be ultra-light., 14 pages, 3 figures; V2: Minor edits, Journal version

The effective approach is applied to the analysis of inflationary magnetogenesis. Rather than assuming a particular underlying description, all the generally covariant terms potentially appearing with four space-time derivatives in the effective action have been included and weighted by inflaton-dependent couplings. The higher derivatives are suppressed by the negative powers of a typical mass scale whose specific values ultimately depend on the tensor to scalar ratio. During a quasi-de Sitter stage the corresponding corrections always lead to an asymmetry between the hypermagnetic and the hyperelectric susceptibilities. After presenting a general method for the estimate of the gauge power spectra, the obtained results are illustrated for generic models and also in the case of some non-generic scenarios where either the inflaton has some extra symmetry or the higher-order terms are potentially dominant., 10 pages, 2 figures

Quasars show considerable promise as standard candles in a high-redshift window beyond Type Ia supernovae. Recently, Risaliti, Lusso \& collaborators \cite{Risaliti:2018reu, Lusso:2019akb, Lusso:2020pdb} have succeeded in producing a high redshift Hubble diagram ($ z \lesssim 7$) that supports "a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat $\Lambda$CDM model up to $z \sim 1.5-2$, but strong deviations emerge at higher redshifts". This conclusion hinges upon a log polynomial expansion for the luminosity distance. In this note, we demonstrate that this expansion (or "improvements" thereof) typically can only be trusted up to $z \sim 1.5-2$. As a result, a breakdown in the validity of the expansion may be misinterpreted as a (phantom) deviation from flat $\Lambda$CDM. We further illustrate the problem through mock data examples., Comment: 4 pages; v2 plots added, matches published version

We discuss the energy scales of the explicit breaking terms of the global symmetries U(1)×globalSU(2)gauge2 needed for the quinessential axion (QA) and the ultra-light axion (ULA). The appropriate scale of QA is about 1.48×108GeV.

In this letter we propose a reduction of the $H_0$ tension puzzle by means of a theory of minimally modified gravity which is dubbed VCDM. After confronting the theory with the experiments, we find that the data allow for a low-redshift transition in the expansion history of the universe at either $z\simeq 0.3 $ or $z \simeq 1.8\,$, corresponding to one of the two local minima of the total $\chi^2$. From the bestfit values the total fitness parameter is improved by $\Delta \chi^2 \simeq 12$, for the data set considered. We then infer the local Hubble expansion rate today within this theory by means of low redshift Pantheon data. The resulting local Hubble expansion rate today is $H^{\rm{loc}}_0=73.6\pm1.4$. We find the tension is reduced within the VCDM theory., Comment: 9 pages, 4 figures; minor revision in v5

It was recently pointed out that the existence of dark energy imposes highly restrictive constraints on effective field theories that satisfy the Swampland conjectures. We provide a critical confrontation of these constraints with the cosmological framework emerging from the Salam-Sezgin model and its string realization by Cvetic, Gibbons, and Pope. We also discuss the implication of the constraints for string model building., Matching version to be published in PLB

We investigate the observational viability of a class of $\alpha$-attractors inflationary models in light of the most recent Cosmic Microwave Background (CMB) and Large-Scale Structure (LSS) data. By considering a double-well potential we perform a slow-roll analysis to study the behavior of this class of models, which is a continuous interpolation between the chaotic inflation for large values of $\alpha$ and the universal attractor, i.e., $n_s=1- 2/N$ and $r=\alpha 12/N^2$ for small $\alpha$, where $n_s$ is the scalar spectral index, $r$ is the tensor-to-scalar ratio, and $N$ is the e-fold number. In order to explore the parameter space of the model, we also perform a MCMC analysis and find $\alpha=7.56\pm 5.15$ ($1\sigma$)., Comment: 22 pages, 6 figures, 2 tables. Minor corrections and references added. Version accepted for publication in Physics Letters B

The recently reported result from XENON1T experiment indicates that there is an excess with $3.5\sigma$ significance in the electronic recoil events. Interpreted as new physics, new sources are needed to account for the electronic scattering. We show that a dark fermion $\psi$ with mass about $ \mathcal{O}\left(10\right)$ MeV from semi-annihilation of $Z_3$ dark matter $X$ and subsequent decay of a dark gauge boson $V_\mu$ may be responsible for the excess. The relevant semi-annihilation process is $X+X\rightarrow \overline{X}+V_\mu (\rightarrow \psi + \overline{\psi})$, in which the final $\psi$ has a box-shape energy spectrum. The fast-moving $\psi$ can scatter with electron through an additional gauge boson that mixes with photon kinetically. The shape of the signals in this model can be consistent with the observed excess. The additional interaction with proton makes this model testable in future searches for nucleus recoil as well. Because of the lightness of invisible particle introduced, this scenario requires non-standard cosmology to accommodate the additional radiation component., Comment: 19 pages, 4 figures, published version

We present $\mathcal{N}=1$ supergravity models of mutated hilltop inflation (MHI) for both large and small field sectors. Models with canonical kinetic terms are developed based on a shift symmetric K\"ahler potential in inflaton superfield, and with a superpotential linear in Goldstino superfield. We also construct models with non-canonical kinetic terms for MHI by generalizing the shift symmetry. We found that a good fraction of the models can address the entire branch of MHI in a single framework., Comment: 6 pages, 4 figures, published version

The dS bubbles can nucleate spontaneously during inflation, and will be stretched by the cosmological expansion to astrophysical scale. We report on a novel phenomenon that such a bubble might develop into a gravastar (an ultra-compact object with a dS core) after inflation, which witnessed the occurrence of inflation and would survive till today. It is pointed out that if a primordial gravastar was involved in one of the LIGO/Virgo gravitational wave (GW) events, the post-merger object could be a gravastar that will eventually collapse into a black hole. As a result, the late-time GW ringdown waveform will exhibit a series of "echoes" with intervals increasing with time., 10 pages, 4 figures

A search for dark matter (DM) with mass in the sub-GeV region (0.32-1 GeV) was conducted by looking for an annual modulation signal in XMASS, a single-phase liquid xenon detector. Inelastic nuclear scattering accompanied by bremsstrahlung emission was used to search down to an electron equivalent energy of 1 keV. The data used had a live time of 2.8 years (3.5 years in calendar time), resulting in a total exposure of 2.38 ton-years. No significant modulation signal was observed and 90% confidence level upper limits of $1.6 \times 10^{-33}$ cm$^2$ at 0.5 GeV was set for the DM-nucleon cross section. This is the first experimental result of a search for DM mediated by the bremsstrahlung effect. In addition, a search for DM with mass in the multi-GeV region (4-20 GeV) was conducted with a lower energy threshold than previous analysis of XMASS. Elastic nuclear scattering was used to search down to a nuclear recoil equivalent energy of 2.3 keV, and upper limits of 2.9 $\times$10$^{-42}$ cm$^2$ at 8 GeV was obtained., 7 pages, 5 figures

We show that ultra-light scalar dark matter (fuzzy dark matter) in galaxies has a quantum mechanical typical acceleration scale about 10−10ms−2, which leads to the baryonic Tully-Fisher relation. Baryonic matter at central parts of galaxies acts as a boundary condition for dark matter wave equation and influences stellar rotation velocities in halos. Without any modification of gravity or mechanics this model also explains the radial acceleration relation and MOND-like behavior of gravitational acceleration found in galaxies having flat rotation curves. This analysis can be extended to the Faber-Jackson relation.

Combining intervals of ekpyrotic (ultra-slow) contraction with a (non-singular) classical bounce naturally leads to a novel cyclic theory of the universe in which the Hubble parameter, energy density and temperature oscillate periodically, but the scale factor grows by an exponential factor from one cycle to the next. The resulting cosmology not only resolves the homogeneity, isotropy, flatness and monopole problems and generates a nearly scale invariant spectrum of density perturbations, but it also addresses a number of age-old cosmological issues that big bang inflationary cosmology does not. There may also be wider-ranging implications for fundamental physics, black holes and quantum measurement., 7 pages, 3 figures

Realising de Sitter vacua in string theory is challenging. For this reason it has been conjectured that de Sitter vacua inhabit the Swampland of inconsistent low-energy effective theories coupled to gravity. Since de Sitter is an attractor for $\Lambda$CDM, the conjecture calls $\Lambda$CDM into question. Reality appears sympathetic to this idea as local measurements of the Hubble constant $H_0$ are also at odds with $\Lambda$CDM analysis of Planck data. This tension suggests that the de Sitter state is unstable, thereby implying a turning point in the Hubble parameter. We present a model relieving this tension, which predicts a turning at small positive redshift $z_*$ that is dictated by present-day matter density $\omega_m$. This feature is easily identified by homogeneous surveys covering redshifts $z \leq 0.1$. We comment on the implications for the Swampland program., Comment: v1 4 pages, comments welcome; v2 replacing mistakenly uploaded unfinished version; v3 arguments revised; v4; v5 matches published version, further changes outcome of the review process

We study the dynamics of dark energy in the presence of a 2-form field coupled to a canonical scalar field $\phi$. We consider the coupling proportional to $e^{-\mu \phi/M_{\rm pl}} H_{\alpha \beta \gamma}H^{\alpha \beta \gamma}$ and the scalar potential $V(\phi) \propto e^{-\lambda \phi/M_{\rm pl}}$, where $H_{\alpha \beta \gamma}$ is the 2-form field strength, $\mu, \lambda$ are constants, and $M_{\rm pl}$ is the reduced Planck mass. We show the existence of an anisotropic matter-dominated scaling solution followed by a stable accelerated fixed point with a non-vanishing shear. Even if $\lambda \geq {\cal O}(1)$, it is possible to realize the dark energy equation of state $w_{\rm DE}$ close to $-1$ at low redshifts for $\mu \gg \lambda$. The existence of anisotropic hair and the oscillating behavior of $w_{\rm DE}$ are key features for distinguishing our scenario from other dark energy models like quintessence., Comment: 11 pages, 5 figures

We introduce a class of non-supersymmetric models explaining baryogenesis a la Affleck-Dine, which use a decay of two superheavy scalar fields with close masses. These scalars acquire non-zero expectation values during inflation through linear couplings to a function of an inflaton. After the inflaton decay, the model possesses approximate U(1)-invariance, explicitly broken by a small mass splitting. This splitting leads to the baryogenesis in the early Universe. Resulting baryon asymmetry is automatically small for the scalars with the masses about the Grand Unification scale and larger. It is fully determined by the inflaton dynamics and the Lagrangian parameters, i.e., is independent of initial pre-inflationary conditions for the scalars. As a consequence, baryon perturbations are purely adiabatic. We point out a possible origin of the mass splitting: masses of scalars degenerate at some large energy scale may acquire different loop corrections due to the interaction with the inflaton. Compared to electroweak baryogenesis and conventional Affleck-Dine scenarios, our mechanism generically leads to the proton decay suppressed by the powers of the superheavy scalar masses, which makes this scenario potentially testable., Comment: 6 pages; matches published version

Particle physics models with Peccei-Quinn (PQ) symmetry breaking as a consequence of supersymmetry (SUSY) breaking are attractive in that they solve the strong CP problem with a SUSY DFSZ-like axion, link the SUSY breaking and PQ breaking intermediate mass scales and can resolve the SUSY mu problem with a naturalness-required weak scale mu term whilst soft SUSY breaking terms inhabit the multi-TeV regime as required by LHC sparticle mass limits and the Higgs mass measurement. On the negative ledger, models based on global symmetries suffer a generic gravity spoliation problem. We present a model based on the discrete R-symmetry Z_{24}^R-- which may emerge from compactification of 10-d Lorentzian spacetime in string theory-- where the mu term and dangerous proton decay and R-parity violating operators are either suppressed or forbidden while a gravity-safe PQ symmetry emerges as an accidental approximate global symmetry leading to a solution to the strong CP problem and a weak-scale/natural value for the mu term., 14 pages including two .png figures

The difficulty of building metastable vacua in string theory has led some to conjecture that, in the string theory landscape, potentials satisfy $\left|\nabla V/V\right|\geq c\sim \mathcal{O}(1)$. This condition, which is supported by different explicit constructions, suggests that the EFTs which lead to metastable de-Sitter vacua belong to what is dubbed as swampland. This condition endangers the paradigm of single field inflation. In this paper, we show how scalar excited initial states cannot rescue single field inflation from the swampland, as they produce large local scalar non-gaussianity, which is in conflict with the Planck upper bound. Instead, we demonstrate that one can salvage single field inflation using excited initial states for tensor perturbations, which in this case produce only large flattened non-gaussianity in the tensor bispectrum. We comment on the possible methods one can prepare such excited initial conditions for the tensor perturbations., v1: 8 pages double columns, no figures; v2: references added, matched the PLB version

We point out that the recently proposed Swampland conjecture on the potential gradient can lead to isocurvature perturbations of dark energy, if the quintessence field acquires large quantum fluctuations during high-scale inflation preferred by the conjecture. Also, if the quintessence field is coupled to a dark sector that contains dark matter, isocurvature perturbation of dark matter is similarly induced. Both isocurvature perturbations can be suppressed if the quintessence potential allows a tracker solution in the early Universe. We find that a vector field of mass $\lesssim {\cal O}(1)$ meV is an excellent dark matter candidate in this context, not only because the right abundance is known to be produced by quantum fluctuations during high-scale inflation without running afoul of isocurvature bounds, but also because its coupling to the quintessence does not spoil the flatness of the potential., Comment: 14 pages, 1 figure; (v2) minor changes, Fig. 1 added

Recently, the DAMA/LIBRA collaboration released updated results from their search for the annual modulation signal from Dark Matter (DM) scattering in the detector. Besides approximately doubling the exposure of the DAMA/LIBRA data set, the updated photomultiplier tubes of the experiment allow a lower recoil energy threshold of 1\,keV electron equivalent compared to the previous threshold of 2 keV electron equivalent. We study the compatibility of the observed modulation signal with DM scattering. Due to a conspiracy of multiple effects, the new data at low recoil energies is very powerful for testing the DM hypothesis. We find that canonical (isospin conserving) spin-independent DM-nucleon interactions are no longer a good fit to the observed modulation signal in the standard halo model. The canonical spin-independent case is disfavored by the new data, with best fit points of a DM mass of $\sim 8\,$GeV, disfavored by $5.2\,\sigma$, or a mass of $\sim 54\,$GeV, disfavored by $2.5\,\sigma$. Allowing for isospin violating spin independent interactions, we find a region with a good fit to the data with suppressed effective couplings to iodine for DM masses of $\sim 10\,$GeV. We also consider spin-dependent DM-nucleon interactions, which yield good fits for similar DM masses of $\sim 10\,$GeV or $\sim 45\,$GeV, Comment: 8 pages, 3 figures. v2: 10 pages, 5 figures. Updated to published DAMA/LIBRA-phase2 data, added results for spin-dependent WIMP-nucleon scattering, and additional references. v3: matches published version

It is well-known that the first-order phase transition (PT) will yield a stochastic gravitational waves (GWs) background with a logo-like spectrum. However, we show that when such a PT happened during the primordial inflation, the GWs spectrum brought by the PT will be reddened, which thus records the unique voiceprint of inflation. We assess the abilities of the GW detectors to detect the corresponding signal., 12 pages, 6 figures

We study a theory of massive tensor gravitons which predicts blue-tilted and largely amplified primordial gravitational waves. After inflation, while their mass is significant until it diminishes to a small value, gravitons are diluted as non-relativistic matter and hence their amplitude can be substantially amplified compared to the massless gravitons which decay as radiation. We show that such gravitational waves can be detected by interferometer experiments, even if their signal is not observed on the CMB scales., 6 pages, 2 figures

We propose that there may be a substantial stochastic gravitational wave background from particle origin, mainly from the gravitational three-body decay of the inflaton. The emitted gravitons could constitute a sizable contribution to dark radiation if the mass of inflaton is close to the Planck scale, which can be probed by future CMB experiments that have a sensitivity on the deviation of the effective number of neutrinos in the standard cosmology, $\delta N_{\textrm{eff}}\sim 0.02 - 0.03$. We have also illustrated the spectrum of the radiated gravitational waves, in comparison to the current and future experiments, and found that gravitational waves from particle origin could be the dominant contribution to the energy density at high-frequency domain, but beyond the sensitivity regions of various experiments., Comment: 1+13 pages, 6 figures; Decay width are updated

There has been recent interest in the evolution and cosmological consequences of global axionic string networks, and in particular in the issue of whether or not these networks reach the scale-invariant scaling solution that is known to exist for the simpler Goto-Nambu and Abelian-Higgs string networks. This is relevant for determining the amount and spectrum of axions they produce. We use the canonical velocity-dependent one-scale model for cosmic defect network evolution to study the evolution of these global networks, confirming the presence of deviations to scale-invariant evolution and in agreement with the most recent numerical simulations. We also quantify the cosmological impact of these corrections and discuss how the model can be used to extrapolate the results of numerical simulations, which have a limited dynamic range, to the full cosmological evolution of the networks, enabling robust predictions of their consequences. Our analysis suggests that around the QCD scale, when the global string network is expected to disappear and produce most of the axions, the number of global strings per Hubble patch should be around $\xi\sim4.2$, but also highlights the need for additional high-resolution numerical simulations., Comment: 7 pages, 1 figure

Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the $\alpha' / \alpha$ parameter related to kinetic mixing of hidden photons and the coupling constant $g_{Ae}$ of axion-like particles in the mass range from 40 to 120 keV/$c^2$, resulting in $\alpha' / \alpha < 6 \times 10^{-26}$ and $g_{Ae} < 4 \times 10^{-13}$. These limits are the most stringent derived from both direct and indirect searches to date., Comment: 18 pages, 5 figures

The recent observation of the 21-cm absorption signal by the EDGES experiment provides a new observational window into the dynamics of the young Universe. Based on this result, we constrain the properties of ALPs and excited dark matter via the energy injections into the gaseous medium that these models produce. In particular, we derive bounds that outperform the present constraints for energy injections in the 10.2 eV to 50 keV range by analysing the intensity of Lyman-$\alpha$ photons and the electron emissivity produced by ionising radiation. Our results also show that once the standard temperature of the soft radiation background is assumed, the explanations of the observed 3.5 keV photon signal within the considered dark matter model are excluded at 95\% confidence level., Comment: 7 pages, 3 figures

We explore the Gravitational Waves (GW) phenomenology of a simple class of supergravity models that can explain and unify inflation and Primordial Black Holes (PBH) as Dark Matter (DM). Our (modified) supergravity models naturally lead to a two-field attractor-type double inflation, whose first stage is driven by Starobinsky scalaron and the second stage is driven by another scalar belonging to a supergravity multiplet. The PBHs formation in our supergravity models is efficient, compatible with all observational constraints, and predicts a stochastic GW background. We compute the PBH-induced GW power spectrum and show that GW signals can be detected within the sensitivity curves of the future space-based GW interferometers such as LISA, DECIGO, TAIJI and TianQin projects, thus showing predictive power of supergravity in GW physics and their compatibility., 6 pages, 1 table, 3 figures. Version 4: revised version accepted to Physics Letters B. Version 5: Fig. 3 updated, a reference added

We consider the Standard Model with three right-handed neutrinos to generate tiny neutrino masses by the seesaw mechanism. Especially, we investigate the case when one right-handed neutrino has the suppressed Yukawa coupling constants. Such a particle has a long lifetime and can produce an additional entropy by the decay. It is then discussed the impact of the entropy production on the gravitational wave background originated in the primordial inflation. We show that the mass and the coupling constants of the long-lived right-handed neutrino can be probed by the distortion of the gravitational wave spectrum, leading to the information of the mass of the lightest active neutrino., Comment: 11 pages, 7 figures

In this paper, we discuss about the possibility to enhance the tensor-to-scalar ratio $r$ under the condition of Trans-Planckian censorship conjecture (TCC), thus $r\sim O(10^{-3})$ could be observable within the sensitivity of future experiments. We make use of the scalar-tensor theory where inflaton is nonminimally coupled to gravity. After demonstrating that the TCC condition could be modified in scalar-tensor theory, we show that due to the effects of modified gravity at the end of inflation, a large $r\sim O(10^{-3})$ could be allowed without violating the TCC. Moreover, the modification can give rise to a weak coupling of gravity to the inflation field. If such an effect has been present as early as inflation starts, it would imply that in our case, the Universe might have experienced an asymptotically safe period at its early time., Comment: 6 pages, 1 figure

Motivated by the recently reported excess in electron recoil events by the XENON1T collaboration, we propose an inelastic fermion dark matter (DM) scenario within the framework of a gauged $L_{\mu}-L_{\tau}$ extension of the standard model which can also accommodate tiny neutrino masses as well as anomalous muon magnetic moment $(g-2)_{\mu}$. A Dirac fermion DM, naturally stabilised due to its chosen gauge charge, is split into two pseudo-Dirac mass eigenstates due to Majorana mass term induced by singlet scalar which also takes part in generating right handed neutrino masses responsible for type I seesaw origin of light neutrino masses. The inelastic down scattering of heavier DM component can give rise to the XENON1T excess for keV scale mass splitting with lighter DM component. We fit our model with XENON1T data and also find the final parameter space by using bounds from $(g-2)_{\mu}$, DM relic, lifetime of heavier DM, inelastic DM-electron scattering rate, neutrino trident production rate as well as other flavour physics, astrophysical and cosmological observations. A tiny parameter space consistent with all these bounds and requirements will face further scrutiny in near future experiments operating at different frontiers., Comment: Version 3: 8 pages, 3 figures; matches version accepted for publication in Phys. Lett. B

We introduce a novel theory of gravity based on the inverse of the Ricci tensor, that we call the anticurvature tensor. We derive the general equations of motion for any Lagrangian function of the curvature and anticurvature scalars. We then demonstrate a no-go theorem: no Lagrangian that contains terms linear in any positive or negative power of the anticurvature scalar can drive an evolution from deceleration to acceleration, as required by observations. This effectively rules out many realizations of this theory, as we illustrate in detail in a particular case. Finally, we speculate on how to circumvent the no-go theorem., 9 pages, 4 figures

An excess in the electronic recoil data was observed in the XENON1T detector. One of plausible explanations for the excess is absorption of a vector bosonic particle with the mass of $2-3\,{\rm keV}$. For this, the kinetic mixing $\kappa\!\sim\!10^{-15}$ of the dark photon with the photon is required if the dark photon explains the current DM abundance. We recently proposed a model where the main component DM today is a decaying warm dark matter (WDM) with the life time comparable to the age of the current universe. The WDM decays to a massless fermion and a massive dark photon. This model was originally designed for addressing both the small scale problems which $\Lambda$CDM suffers from and the $H_{0}$ tension. In this letter, we show that the massive dark photon produced by the WDM decay can be identified with the vector boson inducing the anomalous excess in the XENON1T experiment. Depending on a lifetime of the parent decaying WDM, the dark photon could be either the main component or the sub-component of DM population today., Comment: 5 pages, 3 figures

The recent observation of an excess in the electronic recoil data by the XENON1T detector has drawn many attentions as a potential hint for an extension of the Standard Model (SM). Absorption of a vector boson with the mass of $m_{A'}\!\in\!(2\,{\rm keV},\!3\,{\rm keV})$ is one of the feasible explanations to the excess. In the case where the vector boson explains the dark matter (DM) population today, it is highly probable that the vector boson belongs to a class of the warm dark matter (WDM) due to its suspected mass regime. In such a scenario, providing a good fit for the excess, the kinetic mixing $\kappa\!\sim\!10^{-15}$ asks for a non-thermal origin of the vector DM. In this letter, we consider a scenario where the gauge boson is nothing but the $U(1)_{\rm B-L}$ gauge boson and its non-thermal origin is attributed to the decay of the coherently oscillating scalar of which condensation induces the spontaneous breaking of $U(1)_{\rm B-L}$. We discuss implications for the early universe physics when the warm nature of the vector DM serves as a resolution to both the small scale problems that $\Lambda$CDM model encounters and the XENON1T anomaly., Comment: 5 pages, 1 figure, the way of producing the parent scalar energy density is changed, the conclusion remains unchanged

We establish the nonlocal generalization of the Israel-Stewart model for the relativistic causal thermodynamics of the cosmic fluid, which evolves in the homogeneous isotropic Universe. Based on the second law of thermodynamics we derive the integro-differential master equation for the nonequilibrium pressure scalar and reduce it to the differential equation of the second order in time derivatives. We show that this master equation can be considered as the relativistic analog of the Burgers equation, which is known in the classical theory of viscoelasticity. We obtain the nonlinear key equation, which contains the energy density scalar only, and analyze two exact solutions of the model. The effective temperature is considered to be associated with the barotropic equation of state of the cosmic fluid., 10 pages, 2 figures, revised version published in Phys.Lett.B

We compare two competing relativistic approaches to the N-body simulation of the Universe large-scale structure. To this end, employing the corresponding alternative computer codes ("gevolution" and "screening"), we conduct a series of cosmological simulations in boxes of different sizes and calculate the power spectra of the scalar perturbation $\Phi$, the frame-dragging vector potential ${\bf B}$ and the difference between scalar modes $\chi=\Phi-\Psi$. We demonstrate that the corresponding power spectra are in very good agreement between the compared schemes. For example, the relative difference of the power spectra for $\Phi$ is 0.04% maximum. Since the perturbed Einstein equations have much simpler form in the screening approach, the simulation with this code consumes less computational time, saving almost 40% of CPU hours., Comment: 16 pages, 3 figures

Emission of relativistic axions from transient sources, such as axion star explosions, can lead to observable signatures. We show that axion bursts from collapsing axion stars can be detectable over the wide range of axion masses $10^{-15} \, \textrm{eV} \lesssim m \lesssim 10^{-7} \, \textrm{eV}$ in laboratory experiments, such as ABRACADABRA, DMRadio and SHAFT. The detection of axion bursts could provide new insights into the fundamental axion potential, which is challenging to probe otherwise. An ensemble of bursts in the distant past would give rise to a diffuse axion background distinct from the usual cold axion DM. Coincidence with other signatures would provide a new window into multi-messenger astronomy., 12 pages, 4 figures; matches published version

We elaborate on the mass function of primordial black holes in the case in which the power spectrum of the curvature perturbation is broad. For the case of a broad and flat spectrum, we argue that such a mass function is peaked at the smallest primordial black mass which can be formed and possesses a tail decaying like $M^{-3/2}$, where $M$ is the mass of the primordial black hole., 14 pages, 3 figures

In the inhomogeneous Universe, the cosmological conversion of dark photons into ordinary photons (and vice versa) may happen at a great number of resonance redshifts. This alters the CMB observed energy spectrum and degree of small-scale anisotropies. We utilize results from the EAGLE simulation to obtain the conversion probability along random line-of-sights to quantify these effects. We then apply our results to the case where dark photons are sourced by dark matter decay and their high-redshift conversion into ordinary photons modify the global 21 cm signal expected from the cosmic dawn era. Concretely, we show that a significant portion of the parameter space for which a converted population of photons in the Rayleigh-Jeans tail of the CMB explains the absorption strength observed by EDGES, is ruled out from the brightness temperature measurements of COBE/FIRAS and the CMB anisotropy measurements of Planck and SPT., Comment: 9 pages, 7 figures; numerical bug in Fig. 6 fixed; conclusions unchanged; references added

Scalar weak gravity conjectures (SWGCs) attempt to pinpoint the ranges of couplings consistent with a fundamental theory of all interactions. We identify a generic dynamical consequence of these conjectures for cosmology and show that SWGCs imply a particular behavior of the scalar fields in the early universe. A scalar field that develops a large expectation value during inflation must relax to the minimum of effective potential at a later time. SWGCs imply that a homogeneous distribution of the field is unstable with respect to fragmentation into localized lumps, which could potentially lead to significant consequences for cosmology., 6 pages, 1 figure; v2: publication version

A large experimental program is underway to extend the sensitivity of direct detection experiments, searching for interaction of Dark Matter with nuclei, down to the neutrino floor. However, such experiments are becoming increasingly difficult and costly due to the large target masses and exquisite background rejection needed for the necessary improvements in sensitivity. We investigate an alternative approach to the detection of Dark Matter-nucleon interactions: Searching for the persistent traces left by Dark Matter scattering in ancient minerals obtained from much deeper than current underground laboratories. We estimate the sensitivity of paleo-detectors, which extends far beyond current upper limits for a wide range of Dark Matter masses. The sensitivity of our proposal also far exceeds the upper limits set by Snowden-Ifft et al. more than three decades ago using ancient Mica in an approach similar to paleo-detectors., Comment: 6 pages, 2 figures. v2: significant revisions. v3: matches the published version

The dark glueball (DGB) from a hidden Yang-Mills sector is a simple non-WIMP dark matter candidate characterized by very few parameters. However, it suffers the over dense issue. To overcome it, in general the dark sector is required to be hierarchically cooler than the visible sector. To naturally generate the desired hierarchy, in this paper we introduce higher dimensional operators coupling the dark gauge field strength tensor to the standard model (SM) Higgs doublets or gauge field strength tensors. By tracking the different phases of the universe from the end of inflation, prethermalization, reheating to the radiation dominance era, we show that these operators can make the DGB be a viable dark matter candidate over a wide mass region, from the sub-GeV to multi-PeV or even beyond. At the same time, these operators open decay channels of DGB to the SM species, and partial of the parameter space could leave hints in the cosmic ray., 19 pages, 1 figure

Physics letters / B B809, 1-5 (2020). doi:10.1016/j.physletb.2020.135764, The spontaneous breaking of U(1)$_{B−L}$ around the scale of grand unification can simultaneously account for hybrid inflation, leptogenesis, and neutralino dark matter, thus resolving three major puzzles of particle physics and cosmology in a single predictive framework. The $B−L$ phase transition also results in a network of cosmic strings. If strong and electroweak interactions are unified in an SO(10) gauge group, containing U(1)$_{B−L}$ as a subgroup, these strings are metastable. In this case, they produce a stochastic background of gravitational waves that evades current pulsar timing bounds, but features a flat spectrum with amplitude h$^2$Ω$_{GW}$∼10$^{−8}$ at interferometer frequencies. Ongoing and future LIGO observations will hence probe the scale of $B−L$ breaking., Published by North-Holland Publ., Amsterdam

We consider the gravitational radiation in conformal gravity theory. We perturb the metric from flat Mikowski space and obtain the wave equation after introducing the appropriate transformation for perturbation. We derive the effective energy-momentum tensor for the gravitational radiation, which can be used to determine the energy carried by gravitational waves., Comment: 8 pages, no figures, some errors are corrected

Motivated by the gauge theory of gravity with local scaling symmetry proposed recently in 1712.04537 and 1506.01807, we investigate whether the scalar field therein can be responsible for the inflation. We show that the classical theory would suffer from the difficulty that inflation can start but will never stop. We explore possible solutions by invoking the symmetry breaking through quantum effects. The effective potential of the scalar field is shown to have phenomenologically interesting forms to give viable inflation models. The predictions of physical observables agree well with current cosmological measurements and can be further tested in future experiments searching for primordial gravitational waves., Comment: 1+14 pages, 3 figures, discussions and references updated, published version

Future observations of 21 cm emission from neutral hydrogen survey will become a promising approach to probe the large scale structure of Universe. In this paper, we investigate the impacts of Square Kilometer Array (SKA) 21 cm observation on the estimation of cosmological parameters. We use the simulated data of the baryonic acoustic oscillation (BAO) measurements based on the future SKA experiment with the intensity mapping (IM) technique to do the analysis. For the current observations, we use the latest cosmic microwave background (CMB) observation from {\it Planck} 2018, the optical BAO measurements, and the Type Ia supernovae (SN) observation (Pantheon compilation). We find that the SKA mock data could break the degeneracy between the matter density and the Hubble constant, further improving the cosmological constraints to a great extent. We also find that the constraint on the equation of state parameters of dark energy could be significantly improved by including the SKA mock data into the cosmological global fit., Comment: 8 pages, 3 figures, accepted for publication in PLB

A non-relativistic effective field theory (NREFT) offers a bottom-up framework to classify Dark Matter (DM)-nucleon interactions relevant for scattering at direct detection experiments by organizing the interactions in powers of the momentum transfer $\vec{q}$ and DM velocity $\vec{v}$. This approach generates a number of operators including P-odd and T-odd operators; these can only be generated from a relativistic theory with CP violating interactions. We consider the leading order P-odd, T- odd operators viz. $\mathcal{O}_{10}$, $\mathcal{O}_{11}$ and $\mathcal{O}_{12}$ and compare the constraints on these operators from leading direct detection searches and from the bound on the neutron EDM (nEDM). We perform our analysis using simplified models with charged mediators and compute the loop diagrams contributing to the nEDM. We find that constraints on the DM scattering cross section from the bound on the nEDM are several orders of magnitude stronger than the limits from direct searches, and even well below the neutrino floor for such NREFT operators, for the entire sub-GeV to TeV DM mass range. This indicates that these operators need not be considered when analyzing data from present or future direct dark matter detection experiments., 15 pages, 4 figures, 3 tables, v2: typos corrected; published version is shorter without any major changes